1. Announcements Homework for tomorrow… Ch. 30: Probs. 24, 53, & 56
CQ6: Ia = Id > Ib = Ic
30.8: a) 7.4 x 10-6 m/s b) 2.1 x s
30.16: 4.2 x 106 A/m2
Office hours…
MW 12:30-1:30 pm
TR am
F 1-2 pm
Tutorial Learning Center (TLC) hours:
MW 8-10 am, 12-6 pm R 8-12 pm, 2-6 pm
T 8-1 pm, 2-6 pm F 8-10 am, 2-5 pm

2. Current & Resistance (Resistance and Ohm’s Law)
Chapter 30
Current & Resistance
(Resistance and Ohm’s Law)

3. Review…
Resistivity & conductivity…
Ohm’s Law…
where

4. Resistance and Ohm’s Law
Notice: Ohm’s Law is NOT a Law!
The materials to which Ohm’s law applies are called Ohmic.
i.e.’s: metals and conductors

5. Resistance and Ohm’s Law
Nonohmic materials:
current, I, through the device is NOT directly proportional to the potential difference, ΔV.
i.e.’s: diodes, batteries, and capacitors

6. Quiz Question 1
The current through a wire is measured as the potential difference V is varied.
What is the wire’s resistance?
0.01 .
0.02 .
50 .
100 .
Some other value.

7. Resistance and Ohm’s Law
Q: How does the voltage drop across the wires compare to the voltage drop across the resistor?

8. Resistance and Ohm’s Law
Q: How does the voltage drop across the wires compare to the voltage drop across the resistor?
A: ΔVwire << ΔVresist

9. i.e. 30.8: A battery and a resistor
What resistor would have a 15 mA current if connected across the terminals of a 9.0 V battery?