Current Electricity

Copper and silicon are cooled from 300 K to 60 K, the specific resistance

1. decrease in copper but increase in silicon
2. increase in copper but decrease in silicon
3. increase in both
4. decrease in both

The resistance of each arm of the Wheatstone's bridge is 10 ohm. A resistance of 10 ohm is connected in series with a galvanometer then the equivalent resistance across the battery will be

1. 10 ohm
2. 15 ohm
3. 20 ohm
4. 40 ohm

If specific resistance of a potentiometer wire is 10-7 m and current flow through it is 0.1 amp., cross-sectional area of wire is 10-6 m2 then potential gradient will be

1. 10-2 volt/m
2. 10-4 volt/m
3. 10-6 volt/m
4. 10-8 volt/m

The net resistance of the circuit between A and B is [figure]

1. 83
2. 143
3. 163
4. 223

A car battery of emf 12 V and internal resistance 5 10-2 , receives a current of 60 amp, from external source, then terminal potential difference of battery is

1. 12 V
2. 9 V
3. 15 V
4. 20 V

Two bulbs of (40 W, 200 V), and (100 W, 200 V). Then correct relation for their resistances

1. R40 < R100
2. R40 > R100
3. R40 = R100
4. no relation can be predicted.

The potentiometer is best for measuring voltage, as

1. it has a sensitive galvanometer and gives null deflection
2. it has wire of high resistance
3. it measures p.d. in closed circuit
4. it measures p.d. in open circuit.