Question

The point in a Meter bridge is at $35.6cm$. If the resistances in the gaps are interchanged,the new balance point is:

• A. $64.4cm$
• B. $56cm$
• C. $41.2cm$
• D. $56.7cm$

Answer 1

The correct option is A $64.4cm$

Case 1

Initial

$\frac{P}{Q}=\frac{l}{100-l}$

Given l $=$ 35.6

$\Rightarrow \frac{P}{Q}=\frac{35.6}{64.4}$

Case 2 :- After interchanging

$\frac{Q}{P}=\frac{l}{100-l}$

$\Rightarrow \frac{64.4}{35.6}=\frac{l}{100-l}$

$6440-64.4l=35.6l$

$\Rightarrow 100l=6440$

$\Rightarrow l=64.4$ cm