Under what conditions current passing through the resistance $R$ can be increased by short circuiting the battery of emf $E_2$. The internal resistances of the two batteries are $r_1$ and $r_2$, respectively :
Answer & explanation
Correct answer: option 4
Current, $i_1=\frac{E_1+E_2}{r_1+r_2+R}$ and $i_2=\frac{E_1}{R+r_1}$
∴ $\frac{E_1}{R+r_1}>\frac{E_1+E_2}{r_1+r_2+R}$
or $E_1 r_2>E_2\left(R+r_1\right)$