Can anyone answer and explain? Thanks.

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1 Answer
Feb 25, 2018

C.

Explanation:

Let,the resistance of each of the three lamp is r,

Now, lamp X and Y are in parallel combination,so their net resistance is rrr+r=r2

They are again in series with lamp Z, so net resistance of the circuit is r+r2=3r2

If the voltage of the battery is V ,then current flowing through the circuit is V3r2=2V3r

So,current flowing through lamp Z is 2V3r

Now,potential drop across lamp X and Y is the same as they are in parallel combination, So the value is (V2V3rr)=V3

So,current flowing through lamp Y is V3r=V3r

So,initially, more current is flowing through lamp Z than X,so it was glowing more.

when X is no more, lamp Z and Y comes in series combination,so net resistance is r+r=2r hence,current flowing through each of them is V2r

So, this value of current is higher w.r.t initial value of current flowing through lamp Y so it becomes glower, but for Z this value has decreased than previous,so its brightness decreases.