Two light bulbs, one of resistance and the other of resistance are connected (a) in parallel and (b) in series. We have to find which bulb is brighter in each case.

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(a)

We first consider the case when the two light bulbs are connected in parallel as shown in the figure below.

As the two bulbs are connected in parallel, potential difference across them will be equal. That is

Therefore, the light bulb with resistance will be brighter than the light bulb with resistance , when the two are connected in parallel.

(b)

When the two light bulbs are connected in series as shown in the figure above, the same current i flows through their resistances and . Therefore,

Therefore, the light bulb with resistance will be brighter than the light bulb with resistance .