A 40 watt filament light bulb and a 100 watt filament light bulb are connected in series to a battery. Which bulb will glow brighter? Why? Explain.

100 watt

Explanation:

In parallel the 100w bulb will glow brighter.

The 100w bulb has a lower resistance of the two. That’s why it uses more power normally.

In series, the same current must flow through the two bulbs. And beacuse the power in each bulb is proportional to the resistance, keeping the current constant, the bulb with the highest resistance will glow brightest.

Ignoring the effect of the heat if the filaments. As the resistance in the glowing wire increases with temperature, the bulb with the highest resistance will glow proporitionally more than the power difference suggests. Likely the 100w bulb will not glow at all.