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Question

# When a current of 2A flows in a battery from negative to positive terminal, the potential difference across it is 12V. If a current of 3A flowing in the opposite direction produces a potential difference of 15V, the EMF of the battery is

A
12.6V
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B
13.2V
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C
13.5V
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D
14V
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Solution

## The correct option is B 13.2VLet the emf of cell =EIn 1st case : V1=E−I1r where r= internal resistance of cell. or 12=E−2r......(1)In 2nd case as current in opposite direction so the equation becomes V2=E+I2r or 15=E+3r....(2)using (1), 15=E+3(E/2−6) or 2.5E=33⇒E=13.2V

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