question_answer

The supply voltage to room is 120V. The resistance of the lead wires is 60. A 60 W bulb is already switched on. What is the decrease of voltage across the bulb, when a 240 W heater is switched on in parallel to the bulb?

A) zero                              

B) 2.9 volt

C) 13.3 volt                       

D) 10.04 volt

Correct Answer: D

Solution :

        Voltage across bulb before heater is switched on, Voltage across bulb after heater is switched on, Hence decrease in voltage  (approximately)