Question

In a potentiometer using two cells in series gives a balance length of $600cm$. When the same cells are connected opposing each other then balance length is $100cm$. The ratio of emf of larger to smaller cell is:

• A. $7:5$
• B. $5:7$
• C. $6:1$
• D. $1:6$

Answer 1

Answer: (A)

$7:5$

Case 1

$\Rightarrow (E_1+E_2)=I\times r\left(600\right)$

Case 2

$\Rightarrow (E_1-E_2)=I\times r\times 100$

$\Rightarrow \frac{E_1+E_2}{E_1-E_2}=\frac{600}{100}$

$E_1+E_2={6E}_1-{6E}_2$

$7E_2=5E_1$

$\Rightarrow \frac{E_1}{E_2}=7/5$