Current Electricity

An electric kettle has two heating coils. When one of the coils is connected to an a.c. source, the water in the kettle boils in 10 minutes. When the other coil is used the water boils in 40 minutes. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be

1. 8 minutes
2. 4 minutes
3. 25 minutes
4. 15 minutes

Fuse wire is a wire of

1. high resistance and high melting point
2. high resistance and low melting point
3. low resistance and low melting point
4. low resistance and high melting point

For a cell terminal potential difference is 2.2 V when circuit is open and reduces to 1.8 V when cell is connected to a resistance of R = 5 . Determine internal resistance of cell (r)

1. 109
2. 910
3. 119
4. 59

Specific resistance of a conductor increases with

1. increase in temperature
2. increase in cross-section area
3. increase in cross-section and decrease in length
4. decrease in cross-section area.

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.