Current Electricity

The resistances in the two arms of the meter bridge are 5 and R respectively. When the resistance R is shunted with an equal resistance, the new balance point is at 1.6 l1. The resistance R is [figure]

1. 10
2. 15
3. 20
4. 25

Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 . The power loss in the wire is

1. 19.2 W
2. 19.2 kW
3. 19.2 J
4. 12.2 kW

A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery, used across the potentiometer wire, has an emf of 2.0 V and a negligible internal resistance. The potentiometer wire itself is 4 m long. When the resistance R, connected across the given cell, has values of (i) infinity, (ii) 9.5 , the balancing lengths on the potentiometer wire are found to be 3 m and 2.85 m, respectively. The value of internal resistance of the cell is

1. 0.25
2. 0.95
3. 0.5
4. 0.75

The resistances of the four arms P, Q, R and S in a Wheatstone's bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be

1. 0.1 A
2. 2.0 A
3. 1.0 A
4. 0.2 A

The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 is

1. 0.8
2. 1.0
3. 0.2
4. 0.5

A wire of resistance 4 is stretched to twice its original length. The resistance of stretched wire would be

1. 8
2. 16
3. 2
4. 4

Two rods are joined end to end, as shown. Both have a cross-sectional area of 0.01 cm2. Each is 1 meter long. One rod is of copper with a resistivity of 1.7 10-6 ohm-centimeter, the other is of iron with a resistivity of 10-5 ohm-centimeter. [figure] How much voltage is required to produce a current of 1 ampere in the rods?

1. 0.00145 V
2. 0.0145 V
3. 1.7 10-6 V
4. 0.117 V

A 12 cm wire is given a shape of a right angled triangle ABC having sides 3 cm, 4 cm and 5 cm as shown in the figure. The resistance between two ends (AB, BC, CA) of the respective sides are measured one by one. Their ratio is [figure]

1. 9 : 16 : 25
2. 27 : 32 : 35
3. 21 : 24 : 25
4. 3 : 4 : 5

Ten identical cells connected in series are needed to heat a wire of length one meter and radius 'r' by 10 in time 't'. How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time 't' ?

1. 20
2. 30
3. 40
4. 10

A cell having an emf and internal resistance r is connected across a variable external resistance R. As the resistance R is increased, the plot of potential difference V across R is given by

1. [figure]
2. [figure]
3. [figure]
4. [figure]