When the two identical cells are connected either in series or in parallel acros

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

Options:

A . 1.2Ω

B . 2Ω

C . 4Ω

D . 4.8Ω

Answer: Option C
:
C
In series the current through the resistor R is

\frac{2 E}{R + 2 r}

In parallel connection, current through the resistor R is

\frac{E}{R + \frac{r}{2}}

I = \frac{2 E}{R + 2 r} = \frac{E}{R + \frac{r}{2}} 2 R + r = R + 2 r R = r r = 4 Ω

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