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Question

Two light bulbs are marked 230 V; 75 W and 230 V; 150 W. If the first bulb has a resistance R, then the resistance of the second is;


  1. (1/4) R 

  2. (1/2)R 

  3. 4R

  4. 2R


Solution

The correct option is B

(1/2)R 


P = V2 /R

For the 1st bulb; R = V2 /P1 = 2302 / 75            ......(i)

For the 2nd bulb; R2 = V2 /P2 = 2302 /150        ......(ii)

from, (i) and (ii); R2 = (1/2) R

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