1. The units of resistivity are:
E.none of these

2. A 60-watt light bulb carries a current of 0.5 ampere. The total charge passing through it in one hour is:
A.120 C
B.3600 C
C.3000 C
D.2400 C
E.1800 C

3. Copper contains 8.4 × 1028 free electrons/m3. A copper wire of cross-sectional area
7.4 × 10–7 m2 carries a current of 1 A. The electron drift speed is approximately:
A.3 × 108 m/s
B.103 m/s
C.1 m/s
D.10–4 m/s
E.10–23 m/s

4. You wish to double the rate of energy dissipation in a heating device. You could:
A.double the potential difference keeping the resistance the same
B.double the current keeping the resistance the same
C.double the resistance keeping the potential difference the same
D.double the resistance keeping the current the same
E.double both the potential difference and current

5. Which one of the following quantities is correctly matched to its unit?
A.power — kW·h
B.energy — kW
C.potential difference — J/C
D.current — A/s
E.resistance — V/C

6. Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is:
A.the same as in B
B.twice that in B
C.half that in B
D.four times that in B
E.one fourth that in B


Five cylindrical wires are made of the same material. Their lengths and radii are

wire 1: length E , radius r

wire 2: lenth 3E /2, radius r/2

wire 3: length E /2, radius r/2

wire 4: length E , radius r/2

wire 5: length 2E , radius r/2

Rank the wires according to their resistances, least to greatest.

A.1, 2, 3, 4, 5
B.5, 4, 3, 2, 1
C.1 and 2 tie, then 5, 3, 4
D.1, 3, 4, 2, 5
E.1, 2, 4, 3, 5

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