Question

A cell of emf 2 V and negligible resistance is connected in series with a resistance of 5 ohm, and a potentiometer wire of resistance 10 ohm. The potential drop per cm if the length of the potentiometer wire is 10 m. The emf of cell which is balanced by 750 cm long wire is :

• A. $\frac{1}{1500}\frac{V}{cm},0.5V$
• B. $\frac{1}{750}\frac{V}{cm},1V$
• C. $\frac{1}{1500}\frac{V}{cm},0.6V$
• D. $\frac{1}{250}\frac{V}{cm},1V$

Answer 1

The correct option is B $\frac{1}{750}\frac{V}{cm},1V$

Part I

$\Rightarrow IR=E$

$I=\frac{2}{15}$

P.D across potentiometer $=$ I x 10

$=\frac{2}{15}\times 10$

$=4/3$ V

$\frac{\Delta V}{l}=\frac{4/3}{250}V/cm$

$=\frac{1}{750}V/cm$

Part 2

$\Rightarrow E_1={IR}_{AB}$

$E_1=\frac{2}{15}.r{l}_{AB}$

$E_1=1V$