Question

Three similar cells, each of emf $2V$ and internal resistance $r$ send the same current through an external resistance of $2\Omega$, when connected in series or in parallel. Then the magnitude of current flowing through the external resistance is :

• A. $0.75A$
• B. $1A$
• C. $1.5A$
• D. zero

Answer 1

Answer: (A)

$0.75A$

Consider the three cells are connected in series, then current $I$ through the circuit is given by,
$I=\frac{3\times 2}{3r+2}$
Now, if the three cells are connected in parallel, then current $I$ through the circuit is,
$I=\frac{2}{\frac{r}{3}+2}$
but,
$\frac{6}{3r+2}=\frac{6}{r+6}$ and $r=2\Omega$
Hence, $I=\frac{3\times 2}{3\times 2+2}=0.75$ Amp.