Current Electricity

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)

The ratio of heat dissipated per second through the resistance 5 and 10 in the circuit given below is: [figure]

1. 4 : 1
2. 2 : 1
3. 1 : 2
4. 1 : 1

A wire of resistance 20 is divided into 10 equal parts. A combination of two parts are connected in parallel and so on. Now resulting pairs of parallel combination are connected in series. The equivalent resistance of final combination is .

The resistances of the platinum wire of a platinum resistance thermometer at the ice point and steam point are 8 and 10 respectively. After inserting in a hot bath of temperature 400 , the resistance of platinum wire is :

1. 10
2. 16
3. 8
4. 2

To measure the internal resistance of a battery, potentiometer is used. For R=10 , the balance point is observed at l=500 cm and for R=1 the balance point is observed at l=400 cm. The internal resistance of the battery is approximately :

1. 0.1
2. 0.3
3. 0.2
4. 0.4