Four identical electrical lamps are labelled 1.5V, 0.5A which describes the condition necessary for them to operate at normal brightness. A 12V battery of negligible internal resistance is connected to lamps as shown, then
The value of R for normal brightness of each lamp is
The value of R for normal brightness of each lamp is
Total power dissipated in circuit when all lamps are normally bright is 24W
Power dissipated in R is 21W when all lamps are normally bright
When the rms voltages V_{L}, V_{C} and V_{R} are measured respectively across the inductor L, the capacitor C and the resistor R in a series LCR circuit connected to an AC source, it is found that the ratio V_{L} : V_{C} : V_{R }= 1 : 2 : 3. If the rms voltage of the AC source is 100 V, then V_{R} is close to :
50 V
70 V
90 V
100 V
Water boils in an electric kettle in 15 minutes after switching on. If the length of the heating wire is decreased to 2/3 of its initial value, then the same amount of water will boil with the same supply voltage in
15 minutes
12 minutes
10 minutes
8 minutes
The three resistance of equal value are arranged in the different combinations shown below. Arrange them in increasing order of power dissipation
I.
II.
III.
IV.
III < II < IV < I
II < III < IV < I
I < IV < III < II
I < III < II < IV
The resistance of the filament of an electric bulb changes with temperature. If an electric bulb rated 220 volt and 100 watt is connected to (220×.8) volt sources, then the actual power would be
100×0.8 watt
100× (0.8)^{2} watt
Between 100×0.8 watt and 100 watt
Between 100× (0.8)^{2} watt and 100×0.8 watt
In the circuit shown in figure, the heat produced in 5 ohm resistance is 10 calories per second. The heat produced in 4 resistance is
1 cal/sec
2 cal/sec
3 cal/sec
4 cal/sec
In the circuit as shown in the figure, the heat produced by 6 ohm resistance due to current flowing in it is 60 calorie per second. The heat generated across 3 ohm resistance per second will be
30 cal
60 cal
120 cal
100 cal
If a wire of resistance 20Ω is covered with ice and a voltage of 210 V is applied across the wire, then the rate of melting of ice is
0.85g/s
1.92g/s
6.56g/s
none of these
An immersion heater is rated 836 watt. It should heat 1 litre of water from to in about
200 sec
150 sec
100 sec
120 sec
An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from room temperature ? The temperature of boiling water is
6.4 minutes
6.3 minute
12.6 minutes
12.8 minutes
A house is served by 220 V supply line in a circuit protected by a 9 ampere fuse. The maximum number of 60 W lamps in parallel that can be turned on, is
44
20
22
33
A heater of 220 V heats a volume of water in 5 minute time. A heater of 110 V heats the same volume of water in
5 minutes
8 minutes
10 minutes
20 minutes
A 500 W heating unit is designed to operate from a 115 volt line. If the line voltage drops to 110 volt, the percentage drop in heat output will be
10.2%
8.1%
8.6%
7.6%