Question

The supply voltage to a room is 120 v. The resistance of the lead wires is 6 . 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?

Answer 1

Answer:

10.04

Explanation:

Voltage = 120v ( Given)

Resistance of wire = 6 (Given)

Resistance of bulb = 120×120/60 = 240

Resistance of heater = 120×120/240 = 60

Voltage across bulb after heater is switched on (V1) = 120/54×48 = 106.6

Voltage across bulb before heater is switched on (V2)= 120/246×240 = 117.07

Decrease in voltage  = V1-V2 = 117.07- 106.6

                                   = 10.04 (approx)

Thus the decrease of voltage will be - 10.04