Current Electricity

At room temperature (27 ), the resistance of a heating element is 50 . The temperature coefficient of the material is 2.4 10-4 C-1. The temperature of the element, when its resistance is 62 , is .

In the given circuit, the terminal potential difference of the cell is : [figure]

1. 3 V
2. 4 V
3. 2 V
4. 1.5 V

Resistance of a wire at 0 , 100 and t is found to be 10 , 10.2 and 10.95 respectively. The temperature t in Kelvin scale is .

Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be to times of its initial length if the water is to be boiled in 15 minutes.

1. increased, 34
2. increased, 43
3. decreased, 34
4. decreased, 43

A heater is designed to operate with a power of 1000 W in a 100 V line. It is connected in combination with a resistance of 10 and a resistance R, to a 100 V mains as shown in figure. For the heater to operate at 62.5 W, the value of R should be . [figure]

The value of unknown resistance (x) for which the potential difference between B and D will be zero in the arrangement shown, is : [figure]

1. 3
2. 42
3. 6
4. 9

A wire of resistance R and radius r is stretched till its radius became r/2. If new resistance of the stretched wire is x R, then value of x is .

The number of electrons flowing per second in the filament of a 110 W bulb operating at 220 V is : (Given e = 1.6 10-19 C)

1. 1.25 1019
2. 31.25 1017
3. 6.25 1018
4. 6.25 1017

In the given figure R1 = 10 , R2 = 8 , R3 = 4 and R4 = 8 . Battery is ideal with emf 12 V. Equivalent resistance of the circuit and current supplied by battery are respectively : [figure]

1. 12 and 11.4 A
2. 10.5 and 1.14 A
3. 10.5 and 1 A
4. 12 and 1 A

The electric field between the two parallel plates of a capacitor of 1.5 capacitance drops to one third of its initial value in 6.6 when the plates are connected by a thin wire. The resistance of this wire is . (Given, e 3 = 1.1)