Question

The figure shows a meter bridge in which null point is obtained at a length $AD =l$. When a resistance $S ^{\prime}$ is connected in parallel with resistance $S$ the new position of null point is obtained

• A. to the left of D
• B. to the right of $D$
• C. at the same point $D$
• D. to the left of D if $S^{\prime}$ has lesser value than $S$ and to the right of $D$ if $S^{\prime}$ has more value than $S$

Answer 1

Answer: (B)

The working principle of meter bridge is
$\frac{R}{S}=\frac{l}{100-l}$...(i)
When $S ^{\prime}$ is connected in parallel with $S$ we obtain equivalent resistance $S_{e q}$ of $S$ and $S^{\prime}$ which is less than $S$.
Thus if the value of denominator of L.H.S. of eq. (i) decreases then value of denominator of R.H.S. of eq. (i) also decreases.
For this to happen the null point shifts to the right of D.