Posted by **Bob** on Monday, May 4, 2009 at 1:54pm.

(1) 45 micro coulombs of charge is passed through a wire in 35 seconds. How many electrons does this represent? What is the current in the wire?

(2) A piece of copper wire has a resistance of 5 Ohms at 20 degrees celsius. If another piece of copper wire at 0 degrees celsius is 3 times as long and has a cross sectional area that's twice as big, what will its resistance be?

- Physics -
**drwls**, Monday, May 4, 2009 at 6:05pm
(1) The current (in Amperes) is the charge divided by the time. Divide that once again by the electron charge to get the number on electrons per second.

(2) Resistance is proportional to length and inversely proportional to the wire's cross sectional area. Knowing that, what do you think the answer is?

For highest accuracy, you will have to account for the chance in resistivity with temperature. which is quite small over a range from 0 to 20 C.

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