Question

Question No.18
A bulb is rated 60 W, 240 V. If the voltage drops to 120 V, what will be the power consumed?
30 W
15 W
60 W
120 W​

Answer 1

Answer:

30W

..................

Answer 2

Given :

The rated power of the bulb at 240 V = 60 W

To find :

The power consumed by the bulb when the voltage drops to 120 V .

Solution :

Power ,P = ( voltage * voltage ) / resistance

=> P = ( V * V ) / R

Now ,

60 = ( 240 * 240 ) / R

=> R = ( 240 * 240 ) / 60         .....(i)

when voltage drops to 120 V ,

P = ( 120 * 120 ) / R

=> P = ( 120 * 120 ) * 60 / ( 240 * 240 )      {putting the value of R from (i)}

=> P = 15 W

The power consumed by the bulb when the voltage drops to 120 V is 15 W .