Question

A 60W electric lamp connected in series with a room heater is further connected across the mains. If 60 W lamp is now replaced by a 100W lamp, will the heat produced by the heater be smaller, remain the same or be larger and why?

Solution

Resistance,R=V2/P. So, bulb with greater powerhas lesser resistance. Thus among 60 W & 100W bulbs, when the 100 W bulb isinthe circuit, the circuit has lesser equivalentseries resistance. Hence greater current flows. So, more heat would be produced when the heateris connected tothe 100 W lamp in series.

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