Question

Two cells, each of e.m.f. $E$ and internal resistance $r$, are connected in parallel across a resistor $R$. The power dissipated in the resistor $R$. The power dissipated in the resistor is maximum if :-

• A. $R=r$
• B. $R=2r$
• C. $R=\frac{3r}{2}$
• D. $R=\frac{r}{2}$

Answer 1

The correct option is D $R=\frac{r}{2}$

When two cells are connected in parallel, the net internal resistance $r_n=r||r=r/2$
According to maximum power theorem, the maximum power will be dissipated in R when net internal is equal to resistance R, i.e. $R=r/2$