# Week 6 (Sep. 30 - Oct 4)

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

**PHY 202 Lecture:**Charging and discharging capacitors

**Quiz:**Monday.

Homework:

Homework:

- Electromotive force and ohm's law (Ex. 25.1) (Since you did this last week, no need to do it again…)
- Electro-motive force and Faraday's law (Ex. 25.3*),
- Lenz's law (Ex. 25.4),
**Charging a capacitor**(PHY 202 students): Suppose a 12 volt battery is used to charge a 10 micro-farad capacitor through a 100 ohm resistor. (i) What is the final charge on the capacitor (after a very long time)? (ii) At what time will the capacitor be halfway charged? (iii). What is the current flowing through the resistor at this moment in time? And how does this compare to the current the moment just after you turned on the battery?

**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.

- Calibrate your galvanometer using a power supply, some patch cords, and yourself.
- Study the induction of electrical currents in a coil of wire using your galvanometer by sticking a bar magnet into the coil. Is your data consistent with Lenz's law?
- Study the induction of electrical currents in a coil using an electromagnet, both with and without an iron core. Again, is your data consistent with Lenz's law?
- Use a vernier force sensor to weigh an aluminum tube as a magnetic mass and 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? See if you can analyze your data.

**Chapter 25 (3 videos):**

**Chapter 26 (no videos):**