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

As resistance `R = V^(2)/P or R prop 1/P`, so resistance of 100 W bulb is less than that of 60 W bulb. When 60 W bulb in series of heater is replaced by 100 W bulb, the resistance of circuit decreases. Now for the given voltage, more current flows through the circuit. As heat produced `H = I^(2)Rt or H prop I^(2)`, so more heat will be produced by heater.