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

12.6 V

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13.2 V

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13.5 V

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14 V

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Solution

The correct option is B $13.2 V$
Let the emf of cell $= E$
In 1st case : $V_{1} = E - I_{1} r$ where r= internal resistance of cell.
or $12 = E - 2 r . . . . . . (1)$
In 2nd case as current in opposite direction so the equation becomes
$V_{2} = E + I_{2} r$ or $15 = E + 3 r . . . . (2)$
using (1), $15 = E + 3 (E / 2 - 6)$ or $2.5 E = 33 \Rightarrow E = 13.2 V$

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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

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

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