Question

Two bulbs of resistance `40 Omega` and `400 Omega` are in series in a circuit fed with supply current. Which one will glow more ? If one of these bulbs be switched off, will the light in the room increases or decrease ?

Answer 1

Since the bulbs are connected in series, each will carry the same current. We know that light of a bulb is directly proprotional to the heat produced by it and the heat produced, `H = I^(2)Rt`, i.e., `H prop R`. Therefore `400 Omega` bulb will glow more. When one of these bulbs is switched off, the effective resistance of the current in the circuit increses. Since `H prop I^(2)`, therefore, the light in the romm will increase.