Three identical light bulbs are connected in the circuit shown in the figure bel

Question

Three identical light bulbs are connected in the circuit shown in the figure below. After the switch S is closed, what will be true about the brightness of these bulbs? B1 will be brightest and 83 will be dimmest. B3 will be brightest and B1 will be dimmest. All three bulbs will have the same brightness. B2 will be brightest and 83 will be dimmest. B2 will be brightest and B1 will be dimmest. A cylindrical metal rod of length L and diameter D is connected across a battery having no internal resistance. An ammeter in the circuit measures the current to be I. If we now double the diameter of the rod, but change nothing else, the ammeter will read 4I. 2I. I. I/2. I/4.

Explanation / Answer

18)

as the bulbs are in series ,

the current in all bulbs will be same

Hence , all three bulbs will have the same brightness

19)

as the resistance is given as

R = p * L /A

A is the area of cross section

if we double the diamter of of the rod ,

the area of cross section will be 4 times

Rnew = R/4

as V = I * R

I = V/R

the new current will be 4 * I

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