Lectures in PHYS-207 (6)

Week of August 12-16, 2002: THE LAST WEEK OF CLASS

Monday 8/12 -

Tuesday 8/13 -

Wednesday 8/14 - Special Dr. Phil Office Hours: Noon to 4pm

Thursday 8/15 -

Friday 8/16 - FINAL EXAM (Noon-2pm)

Week of August 5-9, 2002

Monday 8/5 - Exam 3. NOTE: We did not cover Reactance, Impedance or Phasor Diagrams -- so these A.C. topics will NOT appear in Exam 3. Last day to turn in Draft Papers (if you were planning to do so, not required).

Tuesday 8/6 - 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. For A.C. circuits with a Resistor only: I and V stay in phase with each other. RL Circuits: I and V out of phase by 90°. RC Circuits: I and V out of phase by -90°. 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). Q17 Take-Home, Due Thursday 8 August.

Wednesday 8/7 - No Class.

Thursday 8/8 - E & M Waves. Turning Maxwell's Equations in E and B, into 2nd order differential equations (Wave Equation) in E or in B. Both give sine or cosine solutions in space and time. Aside: 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). Frequencies LOWER and wavelengths LONGER than visible light (IR infrared, Microwave, Radio waves, ELF extremely low frequency). Traveling E-M Wave, Poynting Vector and Intensity. First Day to turn in Topic 1 Papers. Q17 due. Q18 Take-Home, Due Friday 9 August.

Friday 8/9 - Light and the Great Debate: Is it a particle or a wave? (It's both!) 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. The Law of Reflection. 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".) Rough surfaces and the problem with making a True Black surface. The Law of Refraction - Snell's Law. Light bent at the interface between two media, because the speed of light changes in the media. If going from an high index of refraction media to a lower index media, have a chance for Total Internal Reflection (T.I.R.).Q19/Q20 Take-Home, Due Date CHANGED to Tuesday 13 August, since we haven't covered thin lenses yet. (Click here if you need a copy.)

Week of July 29-August 2, 2002

Monday 7/29 - Biot-Savart law example: circular loop of current carrying wire. Ampere's Law. 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. B-field of a Torroid (torroidal coil; a torus is like a donut). B-field of a sheet of current. B-field of a Solenoid. Comments about winding real coils with thin, varnish insulation. 2nd set of Sample Exams for Exam 3. Q12 in-class.

Tuesday 7/30 - Ampere-Maxwell equation. Faraday's Law of Induction. Demonstrations. Maxwell's Laws. 3rd set of Sample Exams for Exam 3. Q13 in-class. Q14/Q15 Take-Home, Due Thursday 1 August.

Wednesday 7/31 - No Class.

Thursday 8/1 - The Inductor (L). (SI units = Henry = H) Self-Inductance. Back emf, back current. Opposing the status quo. Mutual Inductance between two inductors. 2nd coil responds only to changes in magnetic flux coming from 1st coil. RL Circuit, similar to RC Circuit, except that energy is stored in the magnetic field at the maximum current. 4th set of Sample Exams for Exam 3. Q8, Q10, Q11, Q12 returned. Q14/15 due date extended to Friday.

Friday 8/2 - LC Oscillator circuit. Same 2nd order differential equation as the Simple Harmonic Oscillator (PHYS-205), such as a mass on a spring. Comments ONLY about the RLC Damped Harmonic Oscillator and the Driven RLC Harmonic Oscillator (Amplifier). Alternating Current (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 RMS Voltage as 0.7071 Maximum Voltage. Similar for RMS Current. For resistive only 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. (Will discuss these on Tuesday 6 August 2002.) Why A.C. power? Transformers allow voltage to be raised or lowered. Power lines run at higher voltages to minimize power losses due to Joule heating in the powerlines. Efficiency = Power Used ÷ Total Power Generated. Q3, Q9, Q13 returned. Q16 in-class. Q14/15 due. NOTE: We did not cover Reactance, Impedance or Phasor Diagrams -- so these A.C. topics will NOT appear in Exam 3.

Week of July 22-26, 2002

Monday 7/22 - Exam 2. (Covers through Chapter 28 only)

Tuesday 7/23 - "Magnetism is just like Electricity, only different." 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. 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. Magnetic Force on a Moving Electric Charge - Right-Hand Rule & Uniform Circular Motion. Velocity Selector. 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). Calutron - a mass spectrometer to enrich Uranium atom by atom. Reminder: Leftover problems on Sample Exams for Exam 2.

Wednesday 7/24 - No Class.

Thursday 7/25 - Magnetic Force on a Current Carrying Wire. For a Closed Loop, the net Magnetic Force from a constant B-field is zero. Magnetic Torque on a Current Carrying Wire. Left as is, this system is an osciallator -- the torque goes to zero after 90° and then points the other way. 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. Cyclotron frequency -- no dependence on the radius (constant angular velocity). Hall Effect -- a device with no moving electrical parts -- proves that charge carriers in a current carrying wire are negative, not positive. 1st Full Sample Exams for Exam 3. Q10 in-class.

Friday 7/26 - Exam 2 returned. Sources of Magnetic Fields. The Biot-Savart Law. B-field from a infinitely long straight current carrying wire by direct integration. (Serway has a similar example, but rather than do the integral in x, he does this theta substitution which Dr. Phil does not think is straight forward.)(Dr. Phil will write up his integral.) Magnetic Force between Two Current Carrying Wires. Q11 in-class. NOTE: No new handouts or take-home quizzes this weekend. Fine time to work on your paper.

Week of July 15-19, 2002

Monday 7/15 - Capacitor Network Reduction (continued). (1) Reduce the parallel and series connections one at a time until you have a single equivalent capacitance. You are strongly urged to redraw the circuit at each reduction. (2) Find the charge Q and voltage difference V of the equivalent capacitance. (3) Work backwards through your redrawn circuits -- at each point where you "reveal" another of the real capacitors, you will be able to figure out either its Q or its V, which allows you to solve Q = C V for the other quantity. (4) The energy stored in each capacitor will add up to the energy stored in the equivalent capacitor. 1st Sample Exams for Exam 2. Q5 Due MONDAY. Q6 Take-Home, Due Tuesday 16 July.

Tuesday 7/16 - Electrostatics versus Electrodynamics. Current defined. Resistors and Resistance. The Simplest Circuit: Battery, wires, load (resistor). Ohm's Law. (Ohm's "3 Laws"). Resistance by geometry. 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".) Power dissipated by Joule heating in a resistor. 2nd Sample Exams for Exam 2. Exam 1 returned. Q7 Take-Home, Due Thursday 18 July.

Wednesday 7/17 - No Class.

Thursday 7/18 - For example given in class on Tuesday, 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.) But 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-210 (?) 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. Q8 in-class.

Friday 7/19 - Real batteries consist of a "perfect" battery (Electromotive force = emf) in series with a small internal resistance, r. As chemical reaction in battery runs down, the internal resistance increases. 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. Proper procedure for jump starting a car. (And why doing it wrong ranges from dangerous to deadly.) RC series circuit. Calculus derivation of q(t) for charging capacitor and discharging capacitor. 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. NOTE: We did not have time to start Magnetism and Magnetic Force on a Moving Electric Charge. This topic (along with the Velocity Selector and the Mass Spectrometer) will NOT be on Exam 2. 3rd Sample Exam for Exam 2. Q5 returned. Q9 Take-Home, Due Monday 22 July.

Week of July 8-12, 2002

Monday 7/8 - Electric Potential versus Electric Potential Energy. P.E. is minus the Work. Potential V is similar, but the integral is done on E-field not Force. More importantly the Potential V is an observable quantity. Equipotential lines, where V is constant, are always perpendicular to E-field lines. Simplified equation V = E d. Example: Lighting. Exam 1 Moved to Thursday 7/11. Q2 Due MONDAY. Q3 Due TUESDAY. No In-Class Quiz on Monday.

Tuesday 7/9 - Find components of E by partial derivative of Electric Potential function V. Finding V by direct integration. Conductor in equilibrium is an equipotential throughout. Example: Why charge tends to accumulate on the tips of pointy things. Equipotential contours transition between any arbitrary conducting blow to point charge at infinity. Short review of Sample Exam Problems. Q3 Due by 5pm. Q4 in-class. Return Q1.

Wednesday 7/10 - No Class.

Thursday 7/11 - Exam 1.

Friday 7/12 - Moving from Field Theory to Applications leading to Devices. The Capacitor stores charge +Q on one plate and -Q on second plate, stores energy in the E-field between the plates. Capacitor Equation. Stories: Dr. Phil & the camera flash, US Navy seaman vs. the tank capacitor (Cap-2, Seaman-0). Parallel Plate Capacitor. Some Comments on real batteries. 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 (Started -- finish Monday). Q5 Take-Home, Due Monday 15 July. (Click here if you need a copy.) Return Q2, Q4.

Week of July 1-5, 2002

Monday 7/1 - Distribute Topic 1 (Blue Handout - Book & Movie List). Conductors (metals) versus non-conductors (insulators). Inducing a charge on a conductor. "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.) E-field lines radiate away from a positive point charge; converge towards a negative point charge. If the universe is charge neutral, can have all E-field lines from + charges terminating on - charges. Quiz 1 in-class. 1st Sample Exams for Exam 1.

Tuesday 7/2 - Why use E-fields, when you need the force F = q E anyway? Because it allows us to examine the environment without needing another charge. Direct integration of Electric Force and Electric Field are similar. Examples: Rod in-line with line from point P (1-dimensional integration). Rod perpendicular to line from point P. Thin ring of charge perpendicular to line from point P. Note that in all these cases, we can predict the long range behavior (E-field behaves as a single point net charge), and anticipate the close-in short range behavior. Check Serway's examples (that's your textbook) -- watch out that his notation may be different. Electric Flux. We will be rescheduling Exam 1 for Thursday 11 July. Q2 Take-Home, Due Monday 8 July.

Wednesday 7/3 - No Class.

Thursday 7/4 - FOURTH OF JULY HOLIDAY - No Class.

Friday 7/5 - Class is scheduled. I know it's inconvenient. Gauss' Law for Electricity. Coulomb's constant k versus Permitivity of Free Space (epsilon-naught)Lecture Handout 2-D and 3-D Integration. Lecture Handout: Gauss' Law. Q3 Take-Home, Due probably Tuesday 9 July.

Week of June 24-28, 2002

Thursday 6/27 - Class begins. Introduction to Dr. Phil. Distribute Syllabus. Discuss 19th Century Physics.

Friday 6/28 - Four Fundamental Forces in Nature: Gravity, E & M, Weak Nuclear Force, Strong Nuclear Force. The Realization that Electricity and Magnetism were part of the same Electromagnetic Force was a great triumph of 19th century physics. Franklin's One-Fluid Model of Electricity. Real Electric Charges. Two charges: like charges repel, unlike (opposite) charges attract. Coulomb's Law looks like Newton's Law of Universal Gravity. The Hydrogen Atom: Gravity loses to Electric Force by a factor of 200 million dectillion (!!!).