Question

In the given potentiometer circuit length of the wire $\text{AB}$ is $3\text{m}$ and resistance is $R=4.5\Omega$. The length $\text{AC}$ for no deflection in galvanometer is

• A. $1.5\text{m}$
• B. $2\text{m}$
• C. $1.8\text{m}$
• D. $2.5\text{m}$

Answer 1

The correct option is B $2\text{m}$

Current in the primary circuit, $I_P=\frac{E}{R+r}=\frac{5}{4.5+0.5}=1\text{A}$

The resistance per unit length of the wire , $\gamma =\frac{R}{L}=\frac{4.5}{3}=1.5\Omega /\text{m}$

$E_s=I_P\gamma l$

$3=1\times 1.5l$

$l=\frac{3}{1.5}=2\text{m}$

Hence, option (b) is the correct answer.