Question

In a potention meter of one metre length an unknown emf voltage source is balanced at 60 cm length of potention meter wire, while a 3v battery is balanced at 45 cm length. Then, the emf of the unknown voltage source is :

• A. 3 V
• B. 2.25 V
• C. 4 V
• D. 4.5 V

Answer 1

The correct option is C 4 V

Let $l_1$ and $l_2$ be the balancing length with the cells $E_1$ and $E_2$ respectively, then $E_1=x{l}_1$ and $E_2=x{l}_2$

$\frac{E_1}{E_2}=\frac{l_1}{l_2}$

$\frac{E_1}{3}=\frac{60}{35}$

$E_1=4V$