Question

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
A. `12.6V`
B. `13.2V`
C. `13.5V`
D. `14.0V`

Answer 1

Correct Answer - B
Let `epsi` be emf and r be internal resistance of the battery
In first case, `12=epsi-2r`
In second case, `12=epsi-2r…..(i)`
In second case, `15=epsi=3r…..(ii)`
Substract (ii) from (i), we get, `r=(3)/(5)Omega`
Putting this value of r in eqn. (i), we get `epsi=12+(2xx3)/(5)=(60+6)/(5)=(66)/(5)=13.2V`