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# PH 223 30: 4-5

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## Richard Datwyler

on 15 November 2016

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#### Transcript of PH 223 30: 4-5

A 3.0 mm diameter wire carries a 12 A current when the electric field is 0.085 V/m. What is the wire's resistivity?
A 0.50 mm diameter silver wire carries a 20 mA Current. What are the
Electric field
and Electron drift speed in the wire?
sigma = 6.2 x 10^7 ohm^-1 m^-1
n = 5.8 x 10^28 m^-3
Wire 1 and 2 are made of the same metal. Wire 2 has twice the length and twice the diameter of wire 1. What are the ratios of the resistivity and their resistances ?
Pencil 'lead' is actually carbon. What is the current if a 9.0 V potential difference is applied between the ends of the 0.7 mm diameter, 6.0 cm long lead from a mechanical pencil?
rho = 3.5 x 10 ^5 ohm m
To protect your house you place a 5.0 m tall iron lighting rod. You find that lightning carries 50 kA and lasts up to 50 micro seconds
How much charge is that?
If you don't want the potential difference between top and bottom to exceed 100 V what must the diameter be?
What is the effective resistance?
Individually....
If a 9 V battery was inserted between a and b, how much power would all the resistors dissipate?
This one?
"What is the difference between resistance and resistivity? "
"We probably won't spend much time on superconductivity but what are some applications of that?"
"more on nonohmic materials. "
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