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Q.

The efficiency of a cell when connected to a resistance R is 60%. What will be its efficiency if the external resistance is increased to six times.

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a

10%

b

60%

c

90% 

d

80%

answer is A.

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Detailed Solution

For Ist case

efficiency = 

TPDEMF×100=ER/R+rE=RR+r

0.6=RR+r

Hence r=23R

 In 2nd  case 

x=6R6R+r

Put the value of r and get the answer.

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