Datum: e = 1.6 x 10-19 C
1. Define current. (1)
2. Show, from first principles, that the current in a conductor is given by
I = nAve . Remember to explain each term (n
, A , v ) (5)
3. Do electrons flow clockwise or anticlockwise around the circuit below? (1)
4. A wafer of silicon (n = 5.0 x 1019 m-3) is of thickness
0.50 mm and width 2.0 cm. If a current of 4.8 mA flows through it, what is the
drift speed of the electrons in it? (4)
5. If the wafer in question 4 were thinner, but the current remained the same,
would the electrons drift more slowly or more quickly? (1)
6. What diameter of copper wire (n = 8 x 1028 m-3) would
carry a current of 1.5 A if electrons drifted at 0.52 mms-1? (4)
7. A piece if copper (n = 8 x 1028 m-3) of dimensions 1.0 cm by 1.0
mm by 2.0 mm carries a current of 20 A. What are the maximum and minimum
possible drift speeds of the electrons through the copper? (4,2)
8. A germanium wire of length 2.4 m carries a current of 4.2 mA when electrons
drift at 525 ms-1. How many free electrons are there in the wire? (5)
9. What happens to the value of n as a metal cools down? Why? (1,2)
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