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Homework for tomorrow…
Ch. 30: Probs. 24, 53, & 56
CQ6: I a
= I d
> I b
= I c
30.8: a) 7.4 x 10 -6 m/s
30.16: 4.2 x 10 6 A/m 2 b) 2.1 x 10 -14 s
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Office hours…
MW 12:30-1:30 pm
TR 9-10 am
F 1-2 pm
Tutorial Learning Center (TLC) hours:
MW 8-10 am, 12-6 pm
T 8-1 pm, 2-6 pm
R 8-12 pm, 2-6 pm
F 8-10 am, 2-5 pm

Current & Resistance
(Resistance and Ohm’s Law)

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

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

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

Quiz Question 1
The current through a wire is measured as the potential difference  V is varied.
What is the wire ’ s resistance?
1.
4.
5.
2.
3.
0.01  .
0.02  .
50  .
100  .
Some other value.

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

Resistance and Ohm’s Law
Q: How does the voltage drop across the wires compare to the voltage drop across the resistor?
A: ΔV wire
<< ΔV resist

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?