Question

A cell can be balanced against 110 cm and 100
cm of potentiometer wire, respectively with and
without being short circuited through a
resistance of 10 . Its internal resistance is -

• A. 2.0 ohm
• B. zero
• C. 1.0 ohm
• D. 0.5 ohm

Answer 1

Answer: (C)

1.0 ohm

$E\propto l_{1}andE-\frac{E}{R+r}.r\propto l_2$
$\Rightarrow \frac{r+R}{R}=\frac{l_1}{l_2}$
$\Rightarrow r=(\frac{l_1}{l_2}-1).R$
$=\frac{110-100}{100}\times 10=1\Omega$