Question

When the two identical cells are connected either in series or in parallel across a 4 ohm resistor they send the same current through it. The internal resistance of the cell is

• A. $1.2\Omega$
• B. $2\Omega$
• C. $4\Omega$
• D. $4.8\Omega$

Answer 1

The correct option is C $4\Omega$

In series the current through the resistor R is $\frac{2E}{R+2r}$
In parallel connection, current through the resistor R is $\frac{E}{R+\frac{r}{2}}$
$I=\frac{2E}{R+2r}=\frac{E}{R+\frac{r}{2}}2R+r=R+2rR=rr=4\Omega$