Week 6 (Sep. 29 Oct. 1, 2, 3 )

Read: Induction of Electric Currents (Chap. 25), Arago's mysterious wheel (Chap. 26),

PHY 202 Lecture: Charging and discharging capacitors
Quiz: Monday.

Homework:

  1. Electromotive force and ohm's law (Ex. 25.1) (Since you did this last week, no need to do it again…)
  2. Electro-motive force and Faraday's law (Ex. 25.3*),
  3. Lenz's law (Ex. 25.4),

Laboratory: Magneto-electric induction (Ex. 25.2). In this lab exercise, we will study the induction of electrical currents by magnets (both permanent magnets and electro-magnets). You will need a sensitive galvanometer (micro-ampere scale), a bar magnet, a set of nested coils, a low-voltage power supply, and some connecting wires. Here are the basic steps to the lab (see the lab description in ASG for more details). Be sure to document each part with clear and correct drawings and concise explanations.

  1. Calibrate your galvanometer using a power supply, some patch cords, and yourself. That is: use your own body as the current-limiting resistance in the circuit. Become part of the resistance!
  2. Study the induction of electrical currents in a coil of wire using your galvanometer by sticking a bar magnet into the coil. Try moving the north face both in and out; the south face both in and out; try holding the magnet stationary and moving the coil; try moving them at different speeds. Record your findings in each case. Are your observations consistent with Lenz's law?
  3. Study the induction of electrical currents in a coil using an electromagnet, both with and without an iron core. You will likely need to put a current-limiting resistor in series with the primary coil to prevent shorting the power supply. Again, is your data consistent with Lenz's law?
  4. Use a vernier force sensor to weigh an aluminum tube as (i) a magnetic mass and (ii) a non-magnetic mass falls through it. Be sure to collect data for enough time that you record a second or two of data both before the mass enters the tube and after it leaves the tube. What is going on here? Does the weight of the tube change while the mass is descending? If so: by how much? Can you explain your data? Hint: think about Newton's third law.

Chapter 25 (3 videos):








Chapter 26 (no videos):


Physics 2