*Updated: 18 December 2012 Tuesday.*

Estimated Pre-Finals Grades can be found here. FINAL COURSE GRADES AND BREAKDOWN BY CATEGORY FOR PHYS-1150 Fall 2012

Reminder that ICES Student Course Evaluations are available now online via GoWMU .

Monday 12/10: FINAL EXAM (2:45pm-4:45pm)

Tuesday 12/11: Office Hours.

Wednesday 12/12: Office Hours.

Thursday 12/13: Office Hours.

Friday 12/14: LAST DAY TO MAKE UP EXAMS.

Monday 12/17: Office Hours.

Tuesday 12/18: Grades due at Noon.

Monday 9/3: Labor Day <No Classes>

Tuesday 9/4: Class begins. Introduction to Dr. Phil.

Wednesday 9/5: Static electricity. The Two-Fluid Model of Electricity. Franklin's One-Fluid Model of Electricity. Occaam's Razor. The simple hydrogen atom -- whatever charge is, the charge on the electron (-e) and the proton (+e) exactly cancel. Real Electric Charges. Two charges: like charges repel, unlike (opposite) charges attract. 1 Coulomb of charge is an enormous amount of charge. "Action at a distance" -- Gravity and the Electric Force are not contact forces. The Electric Force between two point charges, Coulomb's Law looks like Newton's Law of Universal Gravity. Four Fundamental Forces in Nature: Gravity, E & M, Weak Nuclear Force, Strong Nuclear Force.

Thursday 9/6: Distribute syllabus. Coulomb of charge is an enormous amount of charge. Two 1.00 C charges separated by 1.00 meters have a force of one-billion Newtons acting on each other. The Hydrogen Atom: Gravity loses to Electric Force by a factor of 200 million dectillion (!!!). The Helium Atom: Putting more than one proton in the nucleus produces enormous forces on the tiny protons -- Need the Neutron and the Strong Nuclear Force (!!!)

- Quiz 1 will be in-class on Friday 7 September 2012. It will be for attendance purposes. If you miss class on Friday, you will be able to get some of the points by downloading Quiz 1A from the website and turning it in.

Friday 9/7: Demo these class web pages. Discussion of Formula Cards. Finding
the net vector electric force F_{E} for a system of point charges.
Remember: In PHYS-1150, Looking at Symmetry and Zeroes (problems where the
answer is zero) as a way of solving problems. Solving a vector Electric Force
problem when there isn't symmetry to render the problem zero. Review of Vector
Force problems (don't blink or you'll miss it). Q1 was in-class for attendance
purposes. If you missed class, you will be able to get some of the points by
downloading Quiz 1A from the website and turning it in. (Click
here for a copy.) Q2 is a Take-Home quiz on
calculating the vector net electric force in a group of point charges,
now due on Tuesday 11 September 2012.

- FYI: Handout: SI Prefixes and Dr. Phil's Simplified Significant Figures.
- FYI: List of Topics covered in PHYS-1130 when Dr. Phil taught it last.

Monday 9/10: Review of Vector Force problems (don't blink or you'll miss
it). How does q_{1} know that q_{2} is there? -- "Action
at a Distance" -- Gravity and the Electric Force are not contact forces.
The mathematical construct of the Electric Field. E is not an observable
quantity. (Side example: Methods of measuring speed v, do not directly measure
speed v. Topic 1 assigned. (Updated Searchable booklist available online
here .)

From PHYS-1130 notes on vectors:Now we need to start dealing with two-dimensional problems in general. Two kinds of numbers: Scalars (magnitude and units) and Vectors (magnitude, units and direction). Adding and subtracting vectors: Graphical method. To generate an analytical method, we first need to look at some Trigonometry. Right Triangles: Sum of the interior angles of any triangle is 180°, Pythagorean Theorem (a² + b² = c²). Standard Angle (start at positivex-axis and go counterclockwise). Standard Form: 5.00m @ 30°. Practical Trigonometry. SOHCAHTOA. Adding and subtracting vectors: Analytical method. (Check to make sure your calculator is set for Degrees mode. Try cos 45° = sin 45° = 0.7071) Why arctangent is a stupid function on your calculator.

**Remember:** PHYS-1160 Lab Begins This
Week.

NOTE: Monday 10 September 2012 -- Physics Help Room starts in 0077 Rood.Web comic XKCD's take on Guide To Converting To Metric. (Both funny and true, but there is some bad language.)

Tuesday 9/11: E-field lines allow us to qualitatively sketch what happens
when two charges are near to each other. (1) +q and -q, (2) +q and +q. Very
close to each point charge, the E-field lines are radial outward, evenly
spaced. In the system, the E-field lines interact with each other -- but
E-field lines can never cross. Long range, the system of point charges looks
like a single net charge. The density of E-field lines in an area gives you an
indication of the strength of the E-field line. The numbers of E-field lines
attached to a point charge is proportional to the charge. E-field lines radiate
away from positive charges and terminate on negative charges. Note that far
from the charges, these systems look like just a single point charge with a net
charge of (1) 0, (2) +2q and (3) +q. Finite objects: Near distances, Far
distances (looks like a point charge) and inbetween (requires PHYS-207 and
calculus). **Conductors** (metals) versus **non-conductors**
(insulators). Conduction electrons in metals -- free to move around.
**Semi-Conductors** sit in the middle. Sometimes they conduct and sometimes
they don't. This means they act like a switch or valve, and this is the basis
for the entire electronics semi-conductor industry. Charging a conductor by
**induction**. **Next up: **Charge distributions -- very much like mass
distributions used to find center-of-mass or moments of inertia.

- Q2 due on Tuesday -- can be turned into the Physics Office (1120/1122 Everett) by 5pm Tuesday.

Wednesday 9/12: Comments on Q2 -- solution already posted on class webpage.
**Charge distributions** -- λ (lambda) (linear charge density, C/m),
σ (sigma) (surface charge density, C/m²), ρ (rho) (volume charge
density, C/m³). Two terms with unfortunately close sounding names:
**Electric Potential Energy** (in Joules) and **Electric Potential** (in
Volts).Electric Potential versus Electric Potential
Energy. P.E. is minus the Work. Potential V is similar, but comes from the
E-field not Force. More importantly the Potential V (really delta-V) is an
observable quantity. Simplified equation V = E d. **Example**: Lighting.
Strength of E-field is important, in part because in air there is a limit to
how big E can get. At breakdown, the E-field is large enough to start ripping
electrons from gas molecules and the positive ions go one way, the electrons go
another, and then we get a "spark" and no longer are static.
E_{max} in air is 3,000,000 N/C.

- The
**Physics Help Room**is now open in 0077 Rood (basement level, underneath the lecture halls -- use Southwest staircase). This semester the Help Room will be staffed with two people most of the time and open from 10-3 MTWRF.

Thursday 9/13: "Fishing" for lightning on a mountain top with
rockets and a voltmeter. **Equipotential surfaces** -- lines of constant
Electric Potential (voltage). **Analogy**: Topographic maps, the
equipotential lines are like the altitude contour lines. A skier's line of
maximum descent down a mountain corresponds to the E-field lines.
**Reminder**: F_{E} and E are vectors, E.P.E. and V are scalars.
E-Fields and Conductors (in Electrostatic Equilibrium). Charges accumulate on
outside of conductors. (1) E-Field lines terminate normal (perpendicular) to
the conductor's surface. (2) E = 0 inside the conductor. (3) Charges tend to
accumulate more on pointy tips of things, which means more E-field lines and
stronger E-fields. Easy to show for a uniformly charged sphere that (2) is true
at center of the sphere, harder to show (2) is true everywhere inside the
sphere. Conductor in equilibrium is an equipotential throughout. Equipotential
lines, where V is constant, are always perpendicular to E-field lines. Why
charge accumulates on the tips of "pointy things". Model a conducting
blob with a blunt end and a pointy end, sort of like a piece of candy corn, by
a large conducting sphere and a smaller conducting sphere, connected together
by a wire so they are all equipotentials, i.e. V = constant. For a charged
sphere, same as a point charge: V = kq/r. While the charge on the tip is less
than the charge on the rest, the surface charge density, σ = q /
Area , is much higher. Q3 Take-Home on vector E-fields and Forces, due
Monday 17 September 2012 in class or by 5pm.

Friday 9/14: Quickie review of some geometry equations: Circumference, Area,
Volume. Coulomb's constant *k* versus
Permitivity of Free Space (ε_{0} epsilon-naught). Introduce
the permeability of free space for magnetism (μ_{0} mu-naught), and
show how these two fundamental constants are connected to the speed of light,
c. **Working toward Gauss's Law for Electricity**. Analogy of a bag around a
light bulb. All the light rays are contained within the bag, no matter the
shape or distance or size. **Electric Flux: **Electric field times Area,
modified by the angle. Simplest examples are E-field perpendicular to surface,
max flux and parallel to surface, no flux. Gauss's Law for Electricity. Derive
for point charge, turns out to be general equation. Take advantage of geometry
and symmetry.

**Q3 Hint:**If you calculate the electric force using Coulomb's Law in part (b), having already done part (a), you're working too hard! (grin) Think of what the E-field found in part (a) is good for...**Sample Exam 1:**I've started posting Sample Exam 1s on the class web page. Some have solutions, some do not -- after all, you don't have the solution in front of you to work with while you are taking the exam. These are real Dr. Phil PHYS-1150 Exam 1s.

Monday 9/17: **Gauss's Law for Electricity**. Derive for point charge,
turns out to be general equation. Take advantage of geometry and symmetry. For
**conducting charged metal sphere** of radius R, all the charge is on the
outside. Two cases: (1) r < R, no q-inside Gaussian suface, no E-field and
(2) r > R, q-inside = Q, so E-field same as a point charge. For **insulated
charged spher**e of radius R, allow the charge to be distributed evenly
throughout. Two cases: (1) r > R, same as metal sphere, same as point
charge, and (2) r < R, E is zero at center and builds up linearly as a
function of r. Note that at r = R, both cases give same value. Two more Gauss's
Law cases: A **line of charge**, λ = Q / L. E-field falls off as 1/r,
not 1/r². A **sheet of charge**, σ = Q / A. E-field is constant.
Infinite line or sheet of charge versus finite line or sheet (need to stay
close to charge and near center, away from edges.)

- NOTE: Q3 can be turned in before Tuesday's class as well, if you need another night to get it to work.

Tuesday 9/18: **Moving from Field Theory to Applications leading to
Devices**. A **battery** is a device which stores energy in a chemical
reaction. When connected to a circuit, postive charges flow from + terminal to
- terminal (or negative charges flow from - terminal to + terminal). There is a
potential difference or delta-V between the terminals of a battery. A **real
battery** will run down if used too long or if one tries to work it too hard.
We will start with **"perfect" batteries **which never run down.
**Start of Capacitors and Capacitance.** The **Capacitor** stores charge
+Q on one plate and -Q on second plate, stores energy in the E-field between
the plates. Stories: Dr. Phil & the camera flash. US Navy seaman vs. the
tank capacitor (Cap-2, Seaman-0). Use Gauss' Law for Electricity to find the
E-field between the plates. Turns out to be twice the E-field from a single
sheet of charge. (Important to know why.) Capacitor
Equation. SI unit for Capacitance is the Farad. 1F is a large capacitor.
Usually deal with µF (microfarad = 1/1,000,000th of a Farad) and pF
(picofarad = 1/1,000,000,000,000th of a Farad). Circuit
diagrams represent the elements of a circuit. So far: battery, wires,
capacitor. Parallel Plate Capacitor.

- There are Sample Exam 1s on the class web page. The format for the hourly exams is two problems -- each with 5 parts.

Wednesday 9/19: Capacitor Equation. SI unit for Capacitance is the Farad. 1F is a large capacitor. Usually deal with µF (microfarad = 1/1,000,000th of a Farad) and pF (picofarad = 1/1,000,000,000,000th of a Farad). Circuit diagrams represent the elements of a circuit. So far: battery, wires, capacitor. Parallel Plate Capacitor. Two devices connected together in a circuit can only be connected two ways: series or parallel. In Parallel, same voltage, share charge. Equivalent capacitor is always larger. In Series, same charge, share voltage. Equivalent capacitor is always smaller. NOTE: Remember to take the last reciprocal! Capacitor Network Reduction problem. Q4 Take-Home on Gauss' Law for Electricity. due on Thursday 20 September 2012 in class or by 5pm. NOTE: You can still turn in Q4 at class on Friday 21 September 2012.

Thursday 9/20: **Capacitor Network Reduction** problem. Use table with
columns for Q = C V. By going back through the intermediate diagrams, it is
possible to know every value of every capacitor in the network. Add a new
column for the energy in each capacitor: Work to assemble charges on a
capacitor = **Energy stored in the capacitor**. U_{c} =
½CV², and find the energy stored in the equivalent capacitor and the
sum of the energy stored in all four of the real capacitors -- if they agree,
then our analysis and calculations are correct! **Making a real capacitor.**
What if not filled with air? Dielectrics -- an insulator where the +/- charge
pairs are free to rotate, even if they do not move. Polarization. Dielectric
constant (κ kappa) and Dielectric strength (E_{max}).

- FYI: Due to a typo in a textbook years and years ago, sometimes you'll see
me write
*k = 8.998 × 10*, instead of^{9}N·m²/C²**k = 8.988 × 10**. Check your formula cards accordingly...^{9}N·m²/C²

Friday 9/21: **Dielectrics** -- an insulator where the +/- charge pairs
are free to rotate, even if they do not move. Polarization. Dielectric constant
(kappa) and Dielectric strength (E_{max}). **Dielectic constant**
increases capacitance over air gap. **Dielectric strength** usually bigger
than E_{max} in air. Both allow you to (a) make bigger capacitors (or
smaller for the same values) and (b) make non-hollow, self-supporting
components. Electrolytic capacitors. Using dielectric to change capacitance for
detection: Studfinder (for carpentry), some computer keyboard keys, biometrics
for security systems. **Electrostatics** versus **Electrodynamics**.
Resistors and Resistance. **Current defined**. Microscopic view of what is
going on inside the wire. Positive current with positive charge carriers is the
same as negative charge carriers (like electrons) going the other way.
Inside the wire, electrons move randomly anyway. There
are so many, they don't need to go fast to create a current -- the "drift
velocity" of electrons is very slow, << 1 m/s. **The
Simplest Circuit:** Battery, wires, load (resistor).Quiz 5 is a Take-Home on
Parallel Plate Capacitors, handed out Friday 21 September 2012, and due on
Monday 24 September 2012 in class or by 5pm.

- Quiz 6 is a Take-Home on a Capacitor Network Reduction problem, it was supposed to be handed out Friday 21 September 2012, and due on Tuesday 25 September 2012 in class or by 5pm. Hard copies will come on Monday, but you can start it now -- it can be handed in at class on Wed. 9/26.

Monday 9/24: **Resistors and Resistance.** Current defined: i = Δ Q
/ Δ t (SI units, Ampere = A). Microscopic view of what is going on inside
the wire. Positive current with positive charge carriers is the same as
negative charge carriers (like electrons) going the other way. Inside the wire,
electrons move randomly anyway. There are so many, they don't need to go fast
to create a current -- the "drift velocity" of electrons is very
slow, << 1 m/s. (1) The net charge of a current carrying wire remains
zero, so have 1.00 A = 1.00 C/sec isn't the same as having 1.00 C of bare
charge lying around. (2) Positive charges moving in same direction as a
positive current is the same as negative charges moving the other way. (3) When
people say electricity moves "at/near the speed of light", it does
not mean the electrons in the wire are moving at the speed of light. It is the
E-field which is moving at the speed of light in the material. (4) Discussion
of microscopic theory of charges in a conductor. Drift velocity is the very
slow net movement of the electrons moving randomly in the wire. Drift velocity
of electrons in copper wire is about 2.23×10^{-4} m/s.
This microscopic theory becomes more important as we go
to smaller and smaller circuit elements in our microchips.
Moore's Law. (5)
The charges are moving in response to an E-Field, because we have a non-zero
δV. We can have an E-field and δV inside a conductor in a circuit
because this is no longer an electrostatic equilibrium problem. **The Simplest
Circuit:** Battery, wires, load (resistor). Ohm's Law: V=IR form. (Ohm's "3 Laws").
**Joule Heating, Power Law:** P = IV (also 3 forms). **Electrocution** --
it's not the voltage, it's the current and the resistance affects the current.
11mA = 0.011A is the danger value across the heart. **Resistivity** is a
property of the material used in a resistor. **Conductance and
conductivity** are the reciprocal of resistance and resistivity.
**Resistance by geometry**. R = ρ (L / A), where ρ = rho =
resistivity of the material (omega·m), L = length and A = cross-sectional
area. If R=constant over operating range, then we say the
material is "ohmic". If R is not constant, it is
"non-ohmic". Example: Because of the temperature dependence of R, the
filament of an incandescent light bulb has a very different R when lit or dark.
Therefore measuring the resistance of a light bulb with an ohm meter is
useless. Kammerleigh Onnes 1916 work on extending the R vs. T curve
toward T = 0 Kelvin. Discovered Superconductivity, where R=0 identically. We
usually treat the wires in a circuit as having R=0, but they usually are not
superconductors. "High temperature" superconductors (liquid nitrogen
temperature, not liquid helium). Q6 Take-Home on a Capacitor Network Reduction
problem, it was supposed to be handed out Friday 21 September 2012, and due on
Tuesday 25 September 2012 in class or by 5pm.

- Q6 can be handed in at class on Wed. 9/26.
- Q5 can be turned in at class on Tue. 9/25.
- If you are using the Testing Center for Exam 1, you must (a) make an appointment at the Testing Center AND (b) send me an e-mail saying that you are taking your Exam 1 at the Testing Center at such-and-such a time, so that I know to send an exam over there.

Tuesday 9/25: If R=constant over operating range, then we say the material is "ohmic". If R is not constant, it is "non-ohmic". Example: Because of the temperature dependence of R, the filament of an incandescent light bulb has a very different R when lit or dark. Therefore measuring the resistance of a light bulb with an ohm meter is useless. Kammerleigh Onnes 1916 work on extending the R vs. T curve toward T = 0 Kelvin. Discovered Superconductivity, where R=0 identically. We usually treat the wires in a circuit as having R=0, but they usually are not superconductors. "High temperature" superconductors (liquid nitrogen temperature, not liquid helium). The "Woodstock of Physics" in 1987. Next topic: Taking more than one resistor at a time -- series and parallel.

- Class time was provided for going over some Sample Exam 1 problems, but not enough questions.
- Note that the series and parallel rules for capacitors and resistors are the opposite of each other.
- Exam 1 material goes through capacitors, capacitor networks and dielectrics. It will NOT include resistors or resistivity.

Wednesday 9/26: Return Q2, Q3. Series and Parallel Resistors: Two devices connected together in a circuit can only be connected two ways: series or parallel. In Series, same current, share voltage. Equivalent resistance is always larger. In Parallel, same voltage, share current. Equivalent resistance is always smaller. Resistor Network Reduction. (Similar rules to Capacitor Network Reduction except "opposite".) For example given in class, Resistor R1 sees the largest current and dissipates the largest amount of energy per second (Power in Watts). This means it is also the most vulnerable. (Story of radio "repair"%call from 4,000,000,000 miles.)

Thursday 9/27: Exam 1.

- If you missed Exam 1, you need to email Dr. Phil so we can schedule a make-up exam.

Friday 9/28: **Discussion of types of real batteries**, especially the
rechargeables (Nicad, NIMH and Li-ion, plus lead-acid) and why things have
changed. **Real batteries** consist of a "perfect" battery
(Electromotive force = emf, also shown as script-E) in series with a small
internal resistance, r. As chemical reaction in battery runs down, the internal
resistance increases. The actual voltage from the battery is the emf voltage
minus the loss from the internal resistance, V = emf - i r . Tip for weak car
battery on cold day: Run headlights for 30 to 90 seconds. High internal
resistance will warm the battery and make it more efficient. **How to jump a
car battery** correctly and safely. (Improper jump can result in hydrogen
explosions, boiling sulfuric acid, etc.) Q7 Take-Home on a Resistor Network
Reduction problem, due Tuesday 2 October 2012, in class or by 5pm.

Monday 10/1: Not all circuits can be reduced by serial and parallel network
analysis. **Kirchhoff's Laws:** (1) The sum of all currents in and out of
any junction must be zero. (2) The sum of all voltage gains and voltage drops
about any closed loop is zero. Practically speaking, if there are N junctions,
then (1) will give you (N-1) unique equations, and if there are M loops that
can be made in the circuit, then (2) will give you (M-1) unique equations. You
will get the same number of equations as you unknown currents through the
resistors. NOTE: EE students and those who have had ECT-2100 (?) may know a
"better" way to solve Kirchhoff's problems. But the brute force
algebra approach has the advantage of being based on the Physics, so has
instructional value. Example
in class with two batteries and 3 resistors had 3 equations in 3 unknowns.
Solution by brute force algebra here . Note that our assumption that
i_{2} goes to the left was wrong, because the solution gives
i_{2} as slightly negative. Minus signs mean "other
direction". In this case, there is a small current going backwards through
the smaller battery, V_{2}. Perhaps this is a charging circuit for a
rechargeable battery?

- If you missed Exam 1 last week, the easiest thing to do is come by Dr. Phil's office on Monday or Tuesday for afternoon Office Hours. I'll be there a little past 2pm.

Tuesday 10/2: Discuss modern **Christmas tree lights**. Bulbs in series,
but each bulb is in parallel with a small resistor, to keep whole string lit
when one bulb burns out. Older sets were either parallel (full 120 volts) or
series (one burned out bulb takes out the whole set). Newest sets use LED
lights, much less current, much longer estimated lifetimes. **Measuring
things** has the potential to change that which we are measuring. In
PHYS-1160 Lab, you are likely using digital multimeters. Ammeters measure
current by connecting in series to the circuit. Voltmeters measure potential
difference by connecting in parallel to the circuit. **The Galvanometer** is
a generic meter. It has a resistance *R _{G}* and the needle moves
in response to a current through a tiny coil. The full-scale deflection
current,

- NOTE: The galvanometer had a resistance R
_{G}= 63.1 Ω and a full-scale deflection current i_{FS}= 1.00 ×10^{-4}A.

Wednesday 10/3: Measuring things has the potential to change that which we
are measuring. In PHYS-1160 Lab, you are likely using digital multimeters.
Ammeters measure current by connecting in series to the circuit. Voltmeters
measure potential difference by connecting in parallel to the circuit. The
Galvanometer is a generic meter. It has a resistance and the needle moves in
response to a current through a tiny coil. **Ammeter**: a galvanometer and a
very small shunt resistor in parallel, together connected in series with the
circuit. **Voltmeter**: a galvanometer amd a very large resistor in series,
together connected in parallel with the circuit. In both cases, the role of the
second resistor is to limit the current to the galvanometer, no matter what the
design criteria of the meter in question. Finally, we checked to see if, in
putting a real ammeter and voltmeter in a circuit, whether the very act of
measuring V and I changes their values. (If you have the numbers from class,
you can show that for a resistor expected 5.00 A and 5.00 V that the changes in
the readings with both meters present won't change the values in our example by
more than 0.01%.) Next up -- the RC circuit.

- NOTE: The numbers we found for the 5.00 A ammeter and
5.00 volt voltmeter resistors were: r
_{s}= 0.001262 Ω and R_{v}= 49,940 Ω. The galvanometer had a resistance R_{G}= 63.1 Ω and a full-scale deflection current i_{FS}= 1.00 ×10^{-4}A. The high resistance wire we used for the shunt resistor in the ammeter had an R/L = 0.000147 Ω/cm. For I = 5.00 A and V = 5.00 volts, the load resistor would be R = 1.00 Ω.

Thursday 10/4: **RC series circuit**. Circuit diagram for
charging capacitor (ignore the calculus part). Who
knew that (ohms) × (farads) = (seconds)? By time t=3RC, a charging
capacitor will reach 95% of its top charge, or a discharging capacitor will be
down to 5% of its original charge. The current, for both charging and
discharging capacitor in an RC circuit, is maximum at time = 0 and goes to zero
over time. The natural number *e* = 2.7182818284590452353602874713527...
provides a way for us to calculate exponential curves using the
e* ^{x}* function of your calculators. To find

- Unfortunately Exam 1 is going back to grader...

Friday 10/5: **Demo Day:** Light bulb boxes for PARALLEL RESISTORS
(unscrew a bulb, remainder stay lit at same brightness), SERIES RESISTORS
(unscrew a bulb and they all go out; put a 100W and a 15W bulb in series and
the smaller bulb lights up okay, but little/no glow from bigger bulb --
remember that light bulb filaments heat up and are non-ohmic resistors, so the
resistance changes over time), and RC CIRCUITS (start with three caps in
series, connected in series with a light bulb. large (bright) initial current,
fades over time as δV on plates builds up. 1 cap or 3 caps in parallel,
takes longer -- RC constant is larger.). The **Magnetism** part of
Electricity & Magentism. "Magnetism is just like Electricity, only
different." Most people are familiar with (1) magnets sticking to some
metals, not others such as stainless steel and (2) if you have two magnets,
they may attract or repel. North and south are analogous to plus and minus
charges. **Real Magnets are dipoles** (North and South ends, linked). Break
a magnet in half, and you either get two new magnets -- or nothing. So far,
there is no evidence that there are Magnetic Monopoles (magnetic charges:
isolated North or South poles). Rules similar to Electric Charges: Unlike poles
attract, like poles repel. The horizontal **magnetic compass** needle
rotates until its North end points North (or rather to the North Magnetic Pole,
which is of course a South pole of the Earth's magnetic core).

Monday 10/8: "Magnetism is just like Electricity, only different."
Most people are familiar with (1) magnets sticking to some metals, not others
such as stainless steel and (2) if you have two magnets, they may attract or
repel. North and south are analogous to plus and minus charges. Real Magnets
are dipoles (North and South ends, linked). Break a magnet in half, and you
either get two new magnets -- or nothing. So far, there is no evidence that
there are Magnetic Monopoles (magnetic charges: isolated North or South poles).
Rules similar to Electric Charges: Unlike poles attract, like poles repel.
**Demos: Cow magnets** -- powerful cylindrical, rounded end magnets which
get dropped into a cow's first stomach, to collect nails, bits of barbed wire,
etc. from continuing on to the cow's other stomachs. **Broken cow magnets**
show a radial crystalline structure due to the alignment of small magnetic
domains -- what makes the magnetic field strong also makes the magnet
physically weak in some directions, hence the breakage across the radially
aligned grains. Dropping a permanent magnet can result in a reduction of its
magnetic field as the shock allows some iron atoms to flip 180° and
therefore cancel instead of add to an adjacent iron atom's magnetic field.
**SI Units for B-field: **(1 Tesla = 1 T). "Other" unit for
B-field: ( 1 Gauss = 1 G ; 1 T = 10,000 G ). **Earth's B-field** is about 1
Gauss at the Earth's surface. Example of the 4T NMR magnet at Michigan Tech and
the 10-foot radius line on the floor and erasing ATM cards within that circle.
The **horizontal compass** needle rotates until its North end points North
(or rather to the North Magnetic Pole, which is of course a South pole of the
Earth's magnetic core); the **vertical compass** rotates so that it lines up
with the B-field along the surface of the Earth at the point. At the Equator,
the vertical magnetic should be parallel to the ground, at the magnetic poles,
it should be perpendicular to the ground. Is the Earth's magnetic field going
to flip some day? And what about Mars. Magnetic
Force on a Moving Electric Charge - **Right-Hand Rule** & **Uniform
Circular Motion**. The origin of Auroras (aurora borealis = northern lights,
aurora australis = southern lights): charged particles from the Sun end up
following the Earth's B-field lines in helical (screwlike) paths towards the
poles -- when these fast moving particles hit the upper atmosphere, they cause
a glow.

- NOTE: Adding another day to Q9 --
**Now due on Wednesday 10/10**. - Although we know that there is a magnetic force, F
_{B}, between two magnets, we're not really interested in that. Instead, we're going straight to magnetic force on a moving electric charge.

Tuesday 10/9: Cyclotron frequency -- no dependence on the radius (constant angular velocity). Velocity Selector - the Magnetic Force is speed dependent, the Electric Force is not. So we can use an E-field to create an Electric Force to cancel the Magnetic Force on a moving charged particle, such that at the speed v = E / B, the particle travels exactly straight with no net force -- any other speed and the particle is deflected into a barrier. Hence a velocity selector "selects" velocities... The Velocity Selector works with both positive and negative charges, but there must be a charge. A mass spectrometer -- a device that sorts particles by mass. Mass Spectrometer - different semi-circular paths for ions of different mass but same velocity. Can determine chemicals, molecules, and separate isotopes (same element, different number of neutrons in nucleus, so different mass -- cannot be separated by chemical means). Mass Spectrometer as Calutron -- detecting or separating isotopes, something that cannot be done by chemical means.

- In the Mass Spectrometer the distance
*d*between two masses after going through a semi-circular path is equal to the difference in the diameters, not the difference in the radii. D = 2r , so... d = D_{2}- D_{1}= 2(r_{2}- r_{1}) . - NOTE: Adding another day to Q9 --
**Now due on Wednesday 10/10**

Wednesday 10/10: Return X1. Magnetic Force on a
Current Carrying Wire. An electric current is a series of moving electric
charges, after all. **Magnetic Torque on a Current Carrying Wire Loop**.
Torque = IAB or IABsin(θ), where A = area enclosed by the coil. Though
derived for a rectangular coil with sides *a* and *b*, it turns out
this is a general result. Left as is, this system is an osciallator -- the
torque goes to zero after 90° and then points the other way and reaches a
maximum at 180°. But if we can reverse the direction of the current after
the torque goes to zero, then the rotation can continue -- and we have a
primitive electric motor. Discussion of simple DC motors. Q9 Take-Home on
Series RC Circuits, due Friday 12 October 2012, in class or by 5pm.

Thursday 10/11: Magnetic Force on a Current
Carrying Wire. An electric current is a series of moving electric charges,
after all. **Demo** -- hey it works and even in the right direction! The
magnetic constant -- the Permeability of Free
Space, µ_{0}, is unusual in that we know the exact
mathematical representation, which is why is given as 4π ×
10^{-7} T·m/A. As we saw earlier, if we calculate
1/sqrt(ε_{0} × µ_{0}), we get the *c* =
speed of light in vacuum -- again showing the fundamental connection between
electricity and magnetism. Magnetic Field loops
from a Current Carrying Wire. B = µ_{0} I / 2 π r , where r
is the radius of the B-field loops. RHR has "two modes". Mode 1 uses
three mutually perpendicular directions for when you have three vectors (A
× B = C is 1-2-3, x-y-z). Mode 2 uses the curling of the fingers to
represent the circulation of a field or the motion of a current, etc., with the
thumb representing the relevent vector or direction.
Magnetic Force between Two Current Carrying
Wires. Combining problems, we find that for two parallel current carrying
wires, with the currents in the same direction, the magnetic field from wire 1
creates an attractive magnetic force on wire 2. And the magnetic field from
wire 2 creates an attractive magnetic force on wire 1. (Two forces, equal and
opposite, acting on each other -- this is exactly as it should be with Newton's
3rd Law.) Anti-parallel currents (wires parallel, but currents in opposite
directions) repel. Crossed currents (wires perpendicular to each other) see no
magnetic force on each other.

- Consider yesterday's discussion about torque on a current loop and making a DC motor. To get more torque, need more current. Or N loops in a coil instead of just one loop. Comments about winding real coils with thin, varnish insulation.
- First sets of Sample Exam 2 posted on class web page.

Friday 10/12: **Magnetic field from a single loop of wire**. B =
(μ_{0})I / 2 R. Approximating a circular current by using a square
of four straight wires. For N loops *in the same space*, B =
N(μ_{0}) I / 2 R. **Gauss' Law for Magnetism** is not as useful
as Gauss' Law for Electricity, because it is always zero (no magnetic
monopoles). However, there is something we can use in a similar way which
involves involving a path along a B-field and the current(s) contained inside
-- **Ampere's Law:** B L = (μ_{0}) I_{enclosed}. Use in a
way similar to the way we used Gauss' Law for Electricity. Use symmetry and
geometry to select your Amperean Loop to your advantage. In a **Solenoid**,
the N loops *are spread out over a length L*, so *n* = N / L.
(*NOTE: Italics added to emphasize that the N-loop coil and the N-loop
solenoid are different.*) B-field of a Solenoid: constant and uniform
B-field inside (away from edges) and zero outside the coil. Use Ampere's Law to
find B-field inside a Solenoid: B = (μ_{0}) N I / L =
(μ_{0}) *n* I. (*NOTE: The BL Amperean paths for the L and R
sides of the Amperean Loop for Ampere's Law are zero because: (1) the B-field
is zero outside the solenoid and (2) for that part of the path which is inside
the solenoid, the B-field and the path are perpendicular, so the term is zero
as well.*) The Solenoid is the magnetic analog of the parallel plate
capacitor for E-fields. **Comments about making a real velocity selecto**r
-- trying to stuff a capacitor for the E-field and a solenoid for the B-field
in the same space! Comments about winding real coils with thin, varnish
insulation.Q10+11 is a DOUBLE Take-Home (two quizzes on one sheet) on Magnetic
Force on a Moving Electric Charge (Q10) and Magnetic Torque on a Square Current
Loop (Q11), due on Tuesday 16 October 2012, in class or by 5pm.

**Operational defnition of the ampere and the coulomb**:*If the Force per length for two wires with a current I separated by 1 meter is F/L = 2 × 10*^{-7}N/m, then I = 1 A exactly. Then in 1 second, 1 C of charge is moved by this 1 A current.- Next week we will use changing B-Fields (changing magnetic flux) to create electric currents. Regenerative braking in electric cars and trains -- turning mechanical energy into electricity.

Monday 10/15: **Faraday's Law of Induction.** A changing magnetic flux
induces a current in a loop of wire. Think of the coil as wanting to maintain
"the status quo". (*The crankly old man who doesn't want anything
to change. "You're adding flux! I don't want more flux!" "You've
added flux, it's steady, I can live with that." "Hey! You're taking
my flux away! Give me back my flux!"*) So if the magnetic flux is
increasing, the induced current creates an induced magnetic field to try to
cancel the flux. If the magnetic flux is decreasing, the induced current
creates an induced magnetic field to try to bolster the flux.
Faraday's Law of Induction. A changing
magnetic flux induces a current, induces an e.m.f., in the circuit,
substituting for the battery as the power source. It is Lenz's Law that gives
us the minus sign in Faraday's Law of Induction. **Demo**: Magnet moving
into a coil, causing current to flow through galvanometer. Turning coil in a
constant magnetic field -- creates a generator (A.C. or D.C.). *See notes for
10/10 on a primitive electric motor.* *Essentially electric motors and
generators are the same devices. Dynamic or Regenerative Braking turns electric
motors into generators -- it takes energy (work) to turn the generator and this
energy is robbed from the vehicle's Kinetic Energy. Hybrid gas-electric cars
use this as do most railroad trains (either electric or diesel-electric).*

- Don't forget about the DOUBLE-QUIZ 10+11 due on Tuesday 10/16!
- The race between the magnets in the tubes demo didn't work right because I was using two broken pieces of cow magnets. Breaking the magnets considerably weakens the magnetic field -- more than just the halves of the two pieces. We'll repeat the demo on Tuesday with two whole cow magnets.
- Second Sample Exam 2 set posted on class web page.

Tuesday 10/16: **Demo**: Lenz Law race between cow magnets dropped
through (a) plastic pipe and (b) non-magnetic aluminum pipe. And second race
between (b) non-magnetic aluminum pipe and (c) non-magnetic copper pipe.
Induced B-fields due to changing B-fields of falling magnets are created by
induced currents and induced emf -- as the magnet enters and leaves a circular
region of metal pipe, it is slowed by magnetic forces between its magnetic
field and the induced B-field. It is Lenz's Law that gives us the minus sign in
Faraday's Law of Induction. **Induction Cook Surfaces: **Heating the bottom
of a metal cooking pot by induction: New type of cooking range uses sealed
induction heating elements instead of exposed hot resistors or open gas fed
flames -- usable for metal pans only. Or we can **prevent heating from Eddy
Currents** in a piece of metal by cutting slots (like a comb) or turning a
slab of metal into a stack of thin sheets separated by insulation, so that we
cannot get large circles of induced currents from changing magnetic flux.
**Hall Effect** -- a device with no moving electrical parts -- proves that
charge carriers in a current carrying wire are negative, not positive, by
looking at a Hall current perpendicular to the wire when there is an applied
B-field passing through the wire. "The 200 Year Hall Effect
Keyboards", will last "forever", but made obsolete in two years
when Windows 95 added three keys.

Wednesday 10/17: **Mutual Inductance** between 2 coils (1 & 2, or
Primary & Secondary). With an AC power source, there is always a changing
flux in the secondary coil from the changing current in the primary coil.
**The Inductor** (L). (SI units = Henry = H)
Self-Inductance. Back emf, back current.
Opposing the *status quo* -- even of its own B-field! Why induction is a
big deal in electronics, industrial motors and electrical power distribution.

Thursday 10/18: **More practical uses for induction: **(First, how
regular fuses and circuit breakers work -- and why that isn't fast enough to
prevent some types of accidents.) Ground Fault Interupt -- if the current
doesn't return via the return wire, because it has found another conductive
path, then the 2 wires (hot and return) total a net-enclosed-current for
Ampere's Law, generating a B-field in a metal ring, detected by an induction
coil wrapped around the ring and this sets off the relay which breaks the
circuit. **Why A.C. power?** Because we can make a transformer (mutual
inductance) and easily raise or lower the voltage by using two coils connected
magnetically by an iron core. Why A.C. circuits are different than D.C. A.C.
Circuits. Voltage is a sine or cosine functions, as is the Current. **Problem:
Average voltage is ZERO. **Need to define a new average, the
Root-Mean-Square. It is the RMS Voltage and
Current that are usually reported in A.C. circuits. **Typical A.C.
frequency** in U.S. is 60 Hz. Need to specify what type of A.C. For sine
wave, define V_{RMS} = 0.7071 V_{Max}. Similar for RMS Current.

Friday 10/19: **Why A.C. power?** Because we can make a transformer
(mutual inductance) and easily raise or lower the voltage by using two coils
connected magnetically by an iron core. V_{2} =
V_{1}N_{2}/N_{1}. D.C. power lines have huge power
losses due to Joule heating, very low efficiency. Efficiency = Power Used
÷ Total Power Generated. Power lines run at higher voltages to minimize
power losses due to Joule heating in the powerlines. Q12 Take-Home on Faraday's
Law of Induction, due on Tuesday 23 October 2012, in class or by 5pm.

- Wikipedia link about the California Condor.
- Article on the Northeast Corridor and some of the history of the railroad electrification mentioned in class. Articles and photos of the Pennsylvania Railroad GG-1 locomotive (an amazing machine which was doomed because it couldn't change from 25Hz to 60Hz AC.) and the PRR/Penn Central/Amtrak Metroliner (the high speed train where half the fleet failed to work on the old 25Hz AC and had to sit for a decade until the conversion happened).

Monday 10/22: **Demo:** "Jumping Rings", making the bulb light,
by Eddy Currents and Induction. Note that the metal rings get HOT, because
there is a large induced current and metal has a low resistance. The split ring
(a) does not get hot and (b) does not jump, because there is no circuit
enclosing the changing magnetic flux. **Some uses for Induction: **Ford test
electric vehicle with inductive charger -- no exposed metal contacts,
everything covered in smooth plastic. Dr. Phil has been advocating for 15-20
years that small charging bricks for all our electronic devices be replaced
with universal charging-by-induction systems. Beginning to see first practical
systems such as Powermat. **Real AC circuits:** For resistive only A.C.
circuits, can still use Ohm's Law, V = I R. Current and Voltage are both sine
waves. Real A.C. circuits may have a Resistive nature, a Capacitive nature and
an Inductive nature. For A.C. circuits with a Resistor only: I and V stay in
phase with each other. For A.C. circuits with a Resistor only: I and V stay in
phase with each other. RC Circuits: I and V out of phase by -90°. (We say
the voltage *lags* the current.) RL Circuits: I and V out of phase by
+90°. (We say the voltage *leads* the current.)
Inductive Reactance, Capacitive Reactance.

- Remember that Exam 2 is on THURSDAY 25 October 2012. (1) We'll take questions from the Sample Exam 2s in class on Tuesday. (2) If you are taking Exam 2 at the Testing Center, make sure you've reserved your time and send me an email so I can have an exam there for you.
- Powermat Wireless Charging System.
- DON'T TRY THIS AT HOME: I have never heard of Coin Shrinking before, but it seems to me that they are getting extremely large induced currents flowing in these coins, something in the 750,000 A range, which probably heats them to be soft enough that the attraction between parallel current paths might cause the coins to contract. Quarters shrunk down to the size of dimes? I suspect that the reason it didn't work so well with a nickel, is that nickel is a pretty hard metal and has a higher melting point. So they probably didn't get a big enough currentl, so instead of shrinking the nickel, they just sort of wrinkled it. (grin).
- Hint: When writing down the capacitive reactance, X
_{C}, and the inductive reactance, X_{L}, be careful to make sure your "C" and "L" don't sort of look the same.

Tuesday 10/23: Inductive Reactance, Capacitive
Reactance. Many A.C. circuits have features of all three components (R, L
and C), so we have to deal with Impedance.
Phasor diagrams (see textbook for diagrams). Treat Resistive Voltage as one
vector and Inductive Voltage minus Capacitive Voltage as a perpendicular
vector. Whole structure rotates at an angular frequency *ω = 2π
f* and we take the y-components at the angle *θ = ω t* to
get the sine-function of the voltage. V-max and Phase angle (φ) just like
finding the magnitude and standard angle from an x- and y-components of a
vector. Minimum impedance is when purely Resistive or when the two Reactances
cancel each other -- the latter is frequency dependent. Can run into problems
if expecting f=60Hz but get f=50Hz or f=25Hz or even 57Hz.

- The interactions of R, L and C in an AC circuit are complex. It is hoped that the phasor diagrams will help give you a visual reference as to the dynamic nature of the interactions of the voltages and the one current they have in common.
- For the Phasor Diagram, draw it at a time other than t=0 as I did in class, so the angle θ isn't zero. That way you'll get non-zero y-components for all the vectors.
- We looked at a Sample Exam 2 problem today -- we can look at more tomorrow, as well.
- Please note that the Physics Help Room will temporarily move from 0077 Rood Hall to 2240 Rood from Wednesday 24 October 2012 to Friday 26 October 2012.

Wednesday 10/24: Review for X2.

- EXAM 2 MOVED TO FRIDAY 26 OCTOBER 2012.
- Please note that the Physics Help Room will temporarily move from 0077 Rood Hall to 2240 Rood from Wednesday 24 October 2012 to Friday 26 October 2012.

Thursday 10/25: The Series RL Circuit.
Very much like the Series RC Circuit, but everything the opposite. RC: Charges
stored on capacitor plates. The current stops when fully charged. Energy is
stored in the electric field between the plates (PE = ½ C V²). RL:
Current (moving charges) moving through coil. The current is at a maximum when
fully energized. Energy is stored in the magnetic field inside the coil (PE =
½ L I²). Who knew that (Henrys) ÷ (ohms) = (seconds)? NOTE:
Technically it is very hard to have a purely inductive circuit, that is just a
battery and an inductor L, because the long thin wire used in the coil's
windings generally has a resistance. Therefore real L circuits are really RL
circuits. This is analagous to the capacitor, where there is a resistance in
the wire connected to the plates of the capacitor, and therefore real C
circuits are really RC circuits. In both cases this means it takes a finite,
non-zero time for the device (L or C) to store energy in its respective field.
LC oscillator. **Comments ONLY about the RLC Damped Harmonic Oscillator**.
Mechanical analogue is the mass-on-a-spring with shock absorbers. Three cases:
Underdamped, overdamped, critically damped. Need a tuned suspension with shock
absorbers to drive a car safely on the road. The Driven Damped Harmonic
Oscillator -- apply an AC signal and if close to the resonant frequency of the
oscillator, becomes an amplifier.

- Please note that the Physics Help Room will temporarily move from 0077 Rood Hall to 2240 Rood from Wednesday 24 October 2012 to Friday 26 October 2012.

Friday 10/26: Exam 2. (Rescheduled on 10/24) Q13 Take-Home on AC
Electricity, due on Wednesday 31 October 2012, in class or by 5pm. *Yes, I
know it says it's due on Tuesday, but there's material we have to cover on
Monday first.*

Monday 10/29: **Phase Angle φ (phi): **Phasor diagrams (see textbook
for diagrams). Treat Resistive Voltage as one vector and Inductive Voltage
minus Capacitive Voltage as a perpendicular vector. Whole structure rotates and
we take the y-components to get the sine-function of the voltage. V-max and
Phase angle φ (phi), or impedance Z, just like finding the magnitude and
standard angle from an x- and y-components of a vector. φ =
tan^{-1} ( (V_{L}-V_{C}) / V_{R} ) =
tan^{-1} ( (X_{L}-X_{C}) / R ). **Changing from AC to
DC or DC to AC: **Old way using motor-generator sets. A **diode** is a
device which only allows current to flow in one direction. A diode in AC only
takes one side of the AC, get choppy DC (pulse power). A diode bridge of four
diodes gets DC from both above and below. **Brief discussion of
semi-conductors**. *n*-type semi-conductors are electron donors -- extra
electrons free to move. *p*-type semi-conductors have "holes"
which move around -- effectively positive charges. A current going from
*p* to *n* at a p-n junction will go through, opposite current will
not. The transistor -- a switch, an amplifiier -- with three types of material,
*p-n-p* or *n-p-n*. **Maxwell's Equations and Hertz's radio wave LC
oscillator **-- the spark gap radio. AM (amplitude
modulation) radio versus FM (frequency modulation) and digital radio.
The Marconi wireless telegraph of the RMS Titanic, and the modern
cellphone.

- Physics Help Room should have been moved back to 0077 Rood as before.
- In part because of the possibilities of weather issues locally from Hurricane Sandy and the "Frankenstorm", Q13 is now due on Wednesday 31 October 2012.

Tuesday 10/30: **Maxwell's Equations** and Hertz's radio wave LC
oscillator -- the **spark gap radio**. **AM (amplitude modulation)**
radio versus **FM (frequency modulation)** and **digital radio**. The
Marconi wireless telegraph of the RMS Titanic, and the modern cellphone. The
**Electromagnetic Wave travels at the speed of light**. c = 300,000,000 m/s
= 186,000 miles/sec, in vacuum. The Great 19th Century Debate: **Is Light a
Particle or a Wave?** (Wave-Particle Duality did not seem obvious at the
time.) Something that is both a wave and a particle is a "wavicle".
**Pure colors** (EM waves, ROYGBIV for visible light) vs. **Perceived
colors** (RGB, CMY, pinks, browns, "white" light).

- Maxwell's Equations: (1) Gauss' Law for Electricity, (2) Gauss' Law for Magnetism, (3) Faraday's Law of Induction, (4) Ampere-Maxwell Law (Ampere's Law with a second term to account for the lack of an actual current going through a charging/discharging capacitor). We call them Maxwell's Equations because he solved these four equations in four unknowns -- but 3½ of them were found by other people, yet Maxwell gets credit for all four. (grin)

Wednesday 10/31: "Normal" human vision, some types of color
blindness. **The Electromagnetic Spectrum**. Visible light (ROYGBIV=red
orange yellow green blue indigo violet). Visible light is 400nm to 750nm (4000
angstroms to 7500 angstroms). Cannot "see" atoms with visable light,
because the atom is about 1 angstrom across (1.00E-10 meters). The visible
light wave is too large to see something that small. Frequencies LOWER and
wavelengths LONGER than visible light (IR infrared, Microwave, Radio waves, ELF
extremely low frequency). IR perceived as heat. Microwave ovens have metal
screens in their windows -- the centimeter-range sized EM waves cannot see the
"small" holes in the screen, so they bounce off the window as if it
were just like the metal in the other five walls. Discussion of how microwave
ovens "cook" food. Frequencies HIGHER and wavelengths SHORTER than
visible light (UV ultraviolet, X-rays, Gamma rays). UVA and UVB, sunglasses.

- Please note that the Physics Help Room will
temporarily move from 0077 Rood Hall to 2240 Rood from Wednesday 24 October
2012 to
**Friday 2 November 2012**. - Interesting: In looking up the Asahi Pentax Quartz Takumar 85mm lens online, I found a reference to the slightly later and more advanced Ultra Achromatic Takumar 85mm f4.5 lens which had quartz and fluorite lenses (NO glass) and could be used from 200 nm (UV) to 1000 nm (IR).

Thursday 11/1: **The Electromagnetic Spectrum. **Visible light
(ROYGBIV=red orange yellow green blue indigo violet). Frequencies HIGHER and
wavelengths SHORTER than visible light (UV ultraviolet, X-rays, Gamma rays).
Visible light is 400nm to 750nm (4000 angstroms to 7500 angstroms). Cannot
"see" atoms with visable light, because the atom is about 1 angstrom
across (1.00E-10 meters). The visible light wave is too large to see something
that small. Discussion of why Superman's X-ray vision cannot work: Normal human
vision -- light either reflected off of objects or directly from light source.
Few X-rays get reflected, so what is the source of the X-rays for Superman to
see? (If he's projecting the X-rays, he's killing anyone he looks at.) Gamma
rays and food irradiation. The energy of a single photon ("particle"
of light) is *E = h f*, where *h = 6.626 × 10 ^{ -34}
J·s *is Planck's constant, a fundamental constant involved in Modern
Physics. (If there was only Classical Physics, then

Friday 11/2: **Magnitude of the Poynting Vector**, *S = Power /
Area*, or Intensity. Energy density from E-field (found in Chapt. 19) and
B-field (found in Chapt. 22). For an E-M wave, *u* = Total energy density,
and half comes from E-field and half from B-field. Ultimately we find *c = E
/ B*, which makes perfect sense when we realize that for the velocity
selector, where we also had a special interaction between an E-field and a
B-field, we got *v = E / B*. **Doppler shifts: **(1) for sound and (2)
for light in classical physics. Light is shifted towards higher frequencies
(blue shift) when source is heading towards you; shifted to lower frequencies
(red shift) when source is heading away from you. **Examples: **Train horn
coming towards you / going away from you; Doppler radar for detecting speeders
and tornados; rotation of stars. Speed of light and time delays in the
universe. Q14 Take-Home on Light as Wave and Particle, due on Tuesday 6
November 2012, in class or by 5pm.

Monday 11/5:** Optics:** **Geometric Optics (empirical)** and
**Physical Optics (more wave and fieldlike**). **Ray Tracing:** Rays from
a spherical source become essentially parallel rays when you are far away. When
a light ray reaches a new material, it can undergo (1) reflection, (2)
absorption, (3) transmission. The Law of
Reflection. Measure all angles from the normal line perpendicular to the
surface. Rough surfaces -- scattering. **The Optical Lever** -- move a
mirror by 10° and the reflected ray moves by 20°. (Dr. Phil's theory
on the origin of "seven years of bad luck for breaking a mirror".)
People tend to not like photographs of themselves, because they are used to
seeing their mirror image -- their normal image, which the rest of us sees,
looks "wrong". **Corner** and **Corner Cube reflectors**

Tuesday 11/6: Small angle between pairs of mirrors -- light gets reflected into wedge and cannot come out. Corner and Corner Cube reflectors. The Law of Refraction - Snell's Law. Light bent at the interface between two media, because the speed of light changes in the media. (Analogy: If you are driving along the road and your right tires go off onto the soft shoulder, they can't go as fast and the car turns towards the shoulder until all four wheels are driving off the road.) Whether refaction bends light towards normal or away, depends on whether going from low to high index of refraction or high to low index of refraction. If going from an high index of refraction media to a lower index media, have a chance for Total Internal Reflection (T.I.R.). This is a "perfect" reflection, better than a mirror. Used in high-end optical systems instead of mirrors. Also useful in fiber optics cables. Dispersion -- in vacuum all speeds of light are the same, but in a medium, there are slighltly different n's for each wavelength. As one goes from a high index of refraction to a low index, increasing the angle of incidence, white light will start breaking into the rainbox spectrum of colors. This is due to dispersion, a change in the speed of light for each wavelength. Where is the fish in the water? What do you see looking up from the bottom of a swimming pool?

Wednesday 11/7: **Light going through a parallel-plano sheet of glass.**
Two interfaces: air-to-glass and glass-back-to-air. Coming down the normal,
0°, no deviation. At any other angle from the normal in air, the ray is
refracted towards the normal in glass and then back out at the original angle
when back in air. However, the light ray is offset from the line the ray
would've followed had the glass not been there. Discussion of trying to see
forward (large angle from normal) through the windows of a bus, train or plane.
Very hard and very expensive to make true parallel-plano surfaces. **Thin
Lenses. **Simplest lens surfaces are spherical (convex = bows out, concave =
bows in) and flat (plano). So some lenses might appear to be biconvex,
plano-convex, biconcave, convex-concave. A biconvex lens is also called a
positive or converging lens. Parallel light rays coming into such a lens will
all pass through the focal point, a distance *f* from the center of the
lens. By itself, could use as a magnifying lens. Concentrating sunlight:
burning paper or popping ants? Ray tracing gets same results as doing Snell's
Law on mulitple curved lens surfaces. Handy not to have to do all that
refraction calculations! Q15 is a Take-Home on Refraction and Snell's Law, due
on Friday 9 November 2012, in class or by 5pm.

Thursday 11/8: **Ray tracing** gets same results as doing Snell's Law on
mulitple curved lens surfaces. Handy not to have to do all that refraction
calculations! Real image formed by
passing three rays through a positive thin lens (biconvex, converging lens). f
= focal length, p = object distance, q = image distance, h = object height, h'
= image height. **Three cases:** object distance *p > 2f* (real,
inverted, reduced image), *2f < p < f* (real, inverted, magnified
image), *p < f* (virtual, upright, magnified image = magnifying glass)
-- latter two not shown here. Zone of Confusion: No solution for *p = f*.

- First sets of Sample Exam 3s on class web page.

Friday 11/9: Return X2. Analytic formula for
object and image. Magnification: *M = h' / h = -q / p*. Use of Muliple
Lenses -- Focal lengths in series add like series capacitors (by reciprocals)
-- one can adjust the working distance to the object or image, or compact or
expand the physical size of the lens. Diopters are the reciprocal of focal
length in meters. Note that some eyepieces to optical devices have some diopter
built in, so that if you add an eyepiece to the eyepiece, the second unit may
be marked for the *total* diopter, not the diopter of that particular
lens. In multiple lenses the effective diopter is just the sum of the diopters.
A flat piece of glass is 0 diopters. Q16 Take-Home on an interesting Prism
problem, due on Tuesday 13 November 2012, in class or by 5pm. Q17
TWO-PAGE Take-Home on the
Biconvex/Positive/Converging Thin Lens, due on Wednesday 14 November 2012, in
class or by 5pm.

*Exam 2 Curve.*

Monday 11/12: Showing how two lenses can be combined, where a Real Image
from Lens 1 becomes a Virtual Object for Lens 2 to create a Real Image from
Lens 2. (You will NOT be asked to do this drawing.) **Physical Optics.**
Based on wave properties of light. **Constructive and Destructive**
Interference. **Anti-Reflection
coating for lenses. Step 1 **- A thin coating of thickness *t* applied
to a glass surface, means that light rays coming in from the air make two
reflections (air to coating, and coating to glass). If the roundtrip distance
of the 2nd reflection is out of phase with the 1st reflection (off by ½
wavelength) then the two reflections can cancel each other. Thickness = half
the round-trip distance, yields a "quarter-wave coating". **Step 2
-** But the roundtrip distance is done in the coating, so need to find the
wavelength in the coating, not the air or glass. **Step 3 -** When a light
ray goes from a low index of refraction to a higher index of refraction, the
reflection gains a ½ wavelength phase shift. If both reflections are the
same kind (low to high, or high to low), then we still get the same quarterwave
anti-reflection solution. If both reflections are different, we get halfwave
anti-reflection coatings.

Tuesday 11/13: **Physical Optics.** Based on wave properties of light.
**Constructive and Destructive** Interference. **Anti-Reflection coating
for lenses. Step 1 **- A thin coating of thickness *t* applied to a
glass surface, means that light rays coming in from the air make two
reflections (air to coating, and coating to glass). If the roundtrip distance
of the 2nd reflection is out of phase with the 1st reflection (off by ½
wavelength) then the two reflections can cancel each other. Thickness = half
the round-trip distance, yields a "quarter-wave coating". **Step 2
-** But the roundtrip distance is done in the coating, so need to find the
wavelength in the coating, not the air or glass. **Step 3 -** When a light
ray goes from a low index of refraction to a higher index of refraction, the
reflection gains a ½ wavelength phase shift. If both reflections are the
same kind (low to high, or high to low), then we still get the same quarterwave
anti-reflection solution. If both reflections are different, we get halfwave
anti-reflection coatings. Back to Anti-Reflection and Max-Reflection coatings
with 0, 1 or 2 half-wavelength shifts upon reflections. This closes the
material for Exam 3. (Special relativity problems on some Sample Exam 3's will
be saved for Final Exam.)

- Sigh. I bring in my Nikon D1H camera, with 24-120mm f3.5-5.6G ED IF Aspherical SWM VR AF-S Nikkor lens and 72mm Nikon L1Bc Skylight filter, so you can see multi-coated optics -- and no one cares. (sigh)

Wednesday 11/14: **Young's Double-Slit Interference. **Light from two
slit sources -- classically the light should travel in a straight line, get two
"light shadows" or bright spots on the target wall. In wave theory,
however, light from two coherent (in-phase) point sources will reach a point
along the centerline, both traveling the same distance so get constructive
interference and a bright spot. At some place offset from centerline, the two
distances will vary by half a wavelength and get destructive interference and a
dark spot. Alternating bright and dark spots as the two distances change.
**Single-Slit Diffraction**. Sikmilarly, we can divide a single slit into an
upper and lower half, and see interference between them. Double-Slit
*plus* Single Slit. (Because those two slits separated by a distance
*d* also have a width *a*.) Get the double-slit's alternating light
and dark bands, attenuated by the wider envelope of the single slit pattern.

Thursday 11/15: **Diffraction Limited. **Resolution limitations due to
the circular aperture diffraction pattern of the "hole" in a lens
(pupil in the eye). A smaller opening makes picture look "sharper"
for a while, due to increased "depth of field". Then diffraction
limiting takes over -- far away cannot tell if a bright light is one source or
two. **Modern Physics **-- goes to size/time/length scales far outside our
normal experience. **Classical Relativity** (two observers, two frames of
reference), **Special Relativity** (speed constant), **General
Relativity** (accelerations or gravity). Q18 Take-Home on anti-reflection
coatings and Young's Double Slit interference, due on Monday 19 November 2012,
in class or by 4pm.

Friday 11/16: Return some Q's. Remember: Dr.
Phil's Simplified Significant Figures. **Einstein's postulates:** (1)
All observers see the same Physics laws. (2) All observers measure the speed of
light in vacuum as c. **Two equations: ** β = v / c
; γ = 1 / sqrt (1 -
β²) . β has no units and must be < 1. γ also has
no units and must be 1 or greater. Topic 2 Worksheets handed out, due Thursday
6 December 2012. (Click here for a copy.)

Monday 11/19: Return Q16. **Special Relativity** (speed constant).
**Einstein's postulates:** (1) All observers see the same Physics laws. (2)
All observers measure the speed of light in vacuum as c.
Beta, gamma, Length Contraction and
Time Dilation. Alpha Centauri is 4.20 LY from Earth (proper length). Those
on a starship see a different distance and experience a different time than the
observer left on the Earth. But both think the other observer is moving at v
< c. No preferred observer in Special Relativity. Two observers cannot agree
on what they see, distance or time. One sees the proper length: a length
measurement where both ends are measured at the same time. One sees the proper
time: a time measurement where beginning and end are measured at the same
place. Experimental confirmation of Special Relativity: put atomic clocks on
aircraft, spacecraft. Difference in time with identical clocks left on the
ground. Review.

Tuesday 11/20: Exam 3.

Wednesday 11/21: WMU Classes end at Noon -- Class does not meet.

Thursday 11/22: Thanksgiving Day. No classes.

Friday 11/23: No classes.

Monday 11/26: **Einstein's postulates: **(1) All observers see the same
Physics laws. (2) All observers measure the speed of light in vacuum as c.
Beta, gamma, Length Contraction and
Time Dilation. Alpha Centauri is 4.20 LY from Earth (proper length). Those
on a starship see a different distance and experience a different time than the
observer left on the Earth. But both think the other observer is moving at v
< c. No preferred observer in Special Relativity. Two observers cannot agree
on what they see, distance or time. One sees the **proper length:** a length
measurement where both ends are measured at the same time. One sees the
**proper time: **a time measurement where beginning and end are measured at
the same place. Two observers cannot agree on the *order* of events,
either. The **concept of "simultaneity**" is gone. **The
Correspondence Principle** -- at some point our Classical Physics results
need to match the Modern Physics results. So when do we need Special
Relativity? For eyeball measurements, we have trouble distiguishing the size of
things that are only off by 10%. That would correspond to a γ = 1.10 --
what would β be? **Another confirmation of Special Relativity:** Muons
(a form of heavy electron) are created in the upper atmosphere -- they're
unstable and will decay. Muons measured at mountaintop -- by sea level, nearly
all should have already decayed. But you detect almost as many at sea level as
on the mountaintop, because the muon lifetime is measured in the muon's rest
frame *not* while we are watching it moving.

Tuesday 11/27: **The Correspondence Principle** -- at some point our
Classical Physics results need to match the Modern Physics results. So when do
we need Special Relativity? For eyeball measurements, we have trouble
distiguishing the size of things that are only off by 10%. That would
correspond to a gamma = 1.10, and a beta = 0.417 c. **Relativistic
momentum**, *p _{rel} = γ mv*, and

- If v = c then you're a photon and β = 1 and γ = µ. When you try to find the length and time, you discover that the universe has zero length and it takes zero time to cross it. Time has no meaning for a photon.
- If v > c, then you could be a tachyon -- if they exist. The problem is, you might end up going back in time.

Wednesday 11/28: **Doppler Shifts with Light**: If light source is moving
toward an observer, they see shorter wavelengths and high frequencies --
**blue shifted**. If light source is moving away from an observer, they see
longer wavelengths and lower frequencies -- **red shifted**. Distant objects
in the universe all appear to be moving away from us, the most distant ones a
considerable fraction of the speed of light. (Since I was covering this next
topic in PHYS-1070 today, used those blackboards today.) **Four Fundamental
Forces in Nature:** Gravity, E & M, Weak Nuclear Force, Strong Nuclear
Force. **The Hydrogen Atom**. Gravity loses to
Electric Force by a factor of 200 million dectillion (!!!). Likewise,
the two protons in the nucleus of the Helium Atom
require the Strong Nuclear Force to overcome the 231 N electric repulsion.
**Isotopes** are the same element (proton number Z), but with different
numbers of neutrons (N). Some isotopes are stable, some are unstable and
undergo radioactive decay. If we didn't have the Strong Nuclear Force making
the Electric Force irrelevent inside the nucleus, then the only element in the
universe would be hydrogen.

Thursday 11/29: **Matter and the Atom.** All models of the atom are
fundamentally wrong at some level. It's the nature of Quantum Mechanics, which
operates at the land of the very small. But we've already used the
"planetary" model of the atom back when we looked at the electron in
orbit of a hydrogen atom, using U.C.M. and Coulomb's Law. Chemistry suggests a
finite number of elements or starting blocks for all materials. Everything made
of individual atoms, as opposed to say the **Velveeta cheese model**, where
you can forever slice the Velveeta ever finer. **Plum pudding model **of the
atom -- some hard bits in a matrix. Rutherford experiment -- firing particles
at a very thin piece of gold foil (discussion of gold leaf), some of the
particles rebounded at nearly 180°. "It was as if I had fired
cannonballs at a piece of paper and some bounced back towards me."
**Better model of the atom: **electrons on the outside (size of the atom is
about 1 angstrom = 1 ×10^{-10} meters) and protons (and neutrons,
not yet discovered) concentrated into a nucleus (about 1 femtometer = 1
×10^{-15} meters). **The Bohr atom** is really quite a triumph
of the Physics of PHYS-1130 and PHYS-1150: We showed early in the semester that
the gravitational attraction between an electron and a proton doesn't matter in
the hydrogen atom, so if we have an electron in a circular orbit about the
proton (or better yet, the nucleus with a total proton charge *Q = +Z e*,
so we can do elements other than hydrogen), then the Coulomb Force provides the
centripetal force for Uniform Circular Motion (UCM). That allows us to find the
speed *v* as a function of the radius *r*. *The notion in Quantum
Mechanics that values for things like electrons can only have certain values is
foreign to Classical Physics. Indeed, in Classical Physics, Planck's constant h
= 0. But think of our lecture hall -- you can only sit in an unoccupied seat.
Each seat exists in a row with only so many seats, each row is at a particular
height above the lecture floor and a particular distance (radius) from the
lecture table. So in our lecture hall, each of you exists in a unique quantized
state. And it takes more work and energy to climb out of the lowest level
(ground state) up to the top of the lecture hall and walk out the door, freed
from 1110 Rood. (grin)* Which leads us to... Niels Bohr postulated that the
electron could only exist in certain orbits, so he proposed that the angular
momentum (*mvr*) can only have integer values of h-bar. This introduces
the principle quantum number *n*. This also means that the circumference
of the orbital is some integer of the electron's deBroglie wavelength -- and we
have a circular standing wave only for those orbits which are allowed. **The
deBroglie wavelength **-- *λ = h / p* -- Wave/Particle Duality
for Matter. Planck's constant -- *h = 6.626 × 10 ^{-34}
J·s* -- a very small number, but it is NOT zero ( h = 0 in Classical
Physics). So the deBroglie wavelength only matters for very small objects, not
Buicks. First day to accept finished Topic 1 Book Reports. (Last day to accept
without penalty is Monday 3 December 2012 by 5pm.)

Friday 11/30: **The Bohr atom**: Niels Bohr postulated that the electron
could only exist in certain orbits, so he proposed that the angular momentum
(*mvr*) can only have integer values of h-bar. This introduces the
principle quantum number *n*. This also means that the circumference of
the orbital is some integer of the electron's deBroglie wavelength -- and we
have a circular standing wave only for those orbits which are allowed. By the
time we get the radius equation, there are only two variables (and both are
integers!): the quantum state number *n* and the proton/element number
*Z*. All the other items are fundamental constants, which when multiplied
together give us "a_{0}", the radius of the n=1 innermost
state of the hydrogen atom, equal to 0.528 ×10^{-10} meters. Twice
that is the diameter, so the size of the hydrogen atom is about an angstrom, as
advertised. Note that the radius goes as n², so the orbitals get big quite
fast. Since this is UCM, knowing the radius means we know the speed *v*.
And that allows us to calculate the classical Kinetic Energy, *KE =
½mv²*. (It turns out that the speeds remain below 0.42 c for all
*n* and *Z*'s for about half the periodic table, so we don't have to
deal with Relativity.) The total energy of each state, En = KE + PE, and in
this problem I shall state that the PE = -2KE. So En = -KE and it ends up being
Z²/n² times more constants. The ground-state or n=1 energy for
hydrogen is -2.18 ×10^{-18} J or -13.6 eV. Now for an electron to
move from one orbit to another, it must gain or lose energy. Going from a
higher *n* to a lower *n*, the difference in the energy is release as
a photon with E = hf. To go from a lower *n* to a higher *n*, the
electron has to absorb a photon of E=hf. And now we have an **explanation of
the spectral lines** which we had once described as "fingerprints for
elements". Burn hydrogen and the light emitted, when run through a prism
will split not into a rainbow, but individual lines of individual colors --
these are emission lines. Take white sunlight, shine it through a prism and
look at the rainbow of colors under a microscope and you will see that
individual lines of color are missing -- these are absoption lines caused by
the hydrogen gas in the Sun's atmosphere removing those colors and moving their
electrons to higher orbits or ionizing completely. Atomic spectra were known
for decades before the Bohr atom, so they were trying to solve the puzzle
backwards -- what they didn't know was that any transition involving the n=1
innermost orbit in hydrogen gave photons in the UV and so the scientists
couldn't see them at the time. If we try to solve the helium atom (Z=2) in a
similar way, we find that with one nucleus and two electrons, we have a
three-body problem and we can't solve that in closed form. However, we can use
our Bohr equations for **hydrogenic ions** (hydrogen-like) which have only
one electron, so we can solve for He^{+}, Li^{+2},
Be^{+3}, B^{+4}, C^{+5}, ... , U^{+91}, etc.
(Click here for the Periodic Table
with derivation of the radius and energy equations on the back.) Second day to
accept finished Topic 1 Book Reports. (Last day to accept without penalty is
Monday 3 December 2012 by 5pm.) Remaining Topic 2 Worksheets handed out. (Click
here for a copy.) Q20 Take-Home on deBroglie
wavelengths, due Tuesday 4 December 2012, in class or by 5pm.

Monday 12/3: Return X3.* *A (very) brief discussion of Atomic and
Nuclear Physics. **How the Periodic Table of Elements is constructed.**
*NOTE: This material is covered more fully in an Atomic & Nuclear Physics
handout, along with the Periodic Table with equations sheet which will be
handed out on Wednesday. *(Click here for the handout (not given in class)
and here for the Periodic Table which
was handed out 4/15.)

- Reminder: Dec. 10 Mon - FINAL EXAM 2:45-4:45pm (2 hours)

Tuesday 12/4: **The Periodic Table:** Counting the numbers of electrons
in each row. s-electrons = 2, p-electrons = 6, d-electrons = 10, f-electrons =
14. So first row has two elements, ending with Z=2 Helium. Second row adds
2+6=8, ending with Z=10 Neon. Third row adds 2+6=8, ending with Z=18 Argon.
Fourth row adds 2+6+10=18, ending with Z=36 Krypton., Fifth row adds 2+6+10=18,
ending with Z=54 Xenon. Sixth row adds 2+6+10+14=32, ending with Z=86 Radon.
**Heisenberg Uncertainty Principle:** (1) Δp_{x} Δx
greater-than-or-equal h / 4 π (h-bar / 2) and (2) ΔE Δt
greater-than-or-equal h / 4 π (h-bar / 2). α, β and γ.
Alpha particles are ^{4}He nuclei. Heavy, but can be stopped by paper
shielding. Beta particles are electrons or their anti-matter cousins,
positrons. More pentetrating, but can be stopped by foil shielding. Gamma rays
are very hard, particle like photons of high energy. They require lead
shielding.

- Upcoming Schedule:
- Q20 Due Tuesday
- Q21 Handed out Wednesday
- Topic 2 Worksheets Due Thursday
- Q21 Due Friday
- Q22 In-Class Short Quiz Friday
- Q23 Check-Out Form with Final Exam

- Remember, if you're using the Testing Center for your Final Exam, reserve your time and send Dr. Phil an email. You may not be able to get the same day/time as the regular Final Exam.

Wednesday 12/5: **Alpha, Beta, Gamma
decays**. Gamma rays are photons, which have neither a charge nor a mass,
so don't change the element and isotope. Alpha particles are the nucleus of
^{4}He, so ejecting an alpha changes both Z and N. Beta decay has three
processes, all of which change the element number: (1) Beta minus is an
electron, (2) Beta plus is a positron -- a positive electron, the antimatter
form of an electron, and (3) Electron capture (e.c.), in which an innermost
electron strays into the nucleus -- equivalent to a beta plus decay. **The
Neutrino** -- "little neutral one". Postualted by Enrico Fermi,
because the trajectories of some decays seemed to violate conservation of
momentum. So the neutrino has no charge, a tiny mass, travels at nearly the
speed of light and carries a bit of momentum and energy. Solar neutrinos and
whether the core of the Sun is still working. In **Nuclear Physics**, the
sum of the parts is more than the total. **Binding Energy or mass defect**
is mass lost by direct conversion to energy via the Einstein relation, E =
mc². The mass of a deuterium nucleus, ^{2}H, is less than the sum
of a proton and neutron. **Fission, Fusion,
Anhiliation:** **Fusion** can build up nuclei to ^{56}Fe and
release energy, **fission** can break up nuclei above ^{56}Fe and
release energy. It takes the supernova of a massive star to drive fusion past
^{56}Fe and create the rest of the Periodic Table -- our solar system
is 2nd generation, since it contains things other than hydrogen. Q21 Take-Home
on the Heisenberg Uncertainty Principle, due Friday 7 December 2012, in class
or by __3pm__. (Click
here for a copy.) *NOTE: (1) Where it says
"For the two cases of the electron in Quiz 22" -- that should be Quiz
20. NOTE: (2) The 3pm late quiz time is because the office will be shutting
down early.*

- REMEMBER: Topic 2 Worksheets due on Thursday 6 December 2012.

Thursday 12/6: Return Q19-20. **Mass defect: **1 amu converts to 931 MeV
-- an electron-volt is 1 eV = 1.602 × 10^{-19} J. **Hot Fusion
vs. Cold Fusion:** (1) Using muons instead of electrons to draw hydrogen
nuclei together. (2) Pons & Fleischman and 1989 announcement on CNN and the
Wall Street Journal. Bad Science: N-rays. How we know what we know. Theory vs.
Experiment. Topic 2 Worksheets due TODAY.

Friday 12/7: Review. Q22 in-class quiz.

- FINALS WEEK Office Hours are posted here.