A heater joined in series with a ` 50 W` bulb is connected to the mains . If the `50 W` bulb is replaced by a `100 W` bulb , then will the heater now give more heat , less heat, or same heat ? Why ?

Explanation

Resistance of 50 watt bulb is more than that of 100 watt bulb. When 100 watt bulb is replaced by 50 watt bulb, connected in series with heater, the resistance of circuit increases and hence current decrease. As `H prop I^(2)`, therefore the heater will now give less heat.