Question

The combination of two identical cells, whether connected in series or parallel combination provides the same current through an external resistance of 2 Ω. The value of internal resistance of each cell is

• A. 2 Ω
• B. 4 Ω
• C. 6 Ω
• D. 8 Ω

Answer 1

Answer: (A)

2 Ω

Answer 2

The correct answer is (A) : 2 Ω

Fig. 1Fig. 2

From above diagram, we get
$i_p = \frac{E}{2+\frac{r}{2}}$ and $i_s = \frac{2E}{2+2r}$
given $i_p = i_s$
$\frac{1}{2+\frac{r}{2}} = \frac{1}{1+r}$
$1 + r = 2 + \frac{r}{2}$
r = 2Ω