Question

In a meter bridge two gaps in the metallic strip are connected by $3\Omega$ and $9\Omega$ resistors. What should be the value of shunt that needs to be added to $9\Omega$ resistor to shift balancing point by $25cm$ ?

• A. $3.0\Omega$
• B. $3.5\Omega$
• C. $4.5\Omega$
• D. $5.0\Omega$

Answer 1

Answer: (C)

(c) The given situation is shown below, Suppose bridge is balanced at a distance / from one end.

Initially in balance condition,
$\frac{3}{l}=\frac{9}{100-l}$
$\Rightarrow l=25cm$
When a shunt $S^{\prime }\Omega$ is connected to $9\Omega$ resistor balance point shifts by $25cm.$
So, new balance length $=25+25=50cm$

As meter bridge is balanced at centre point. This means resistances of left and right gap are equal.
$\Rightarrow 3=\frac{9S}{9+S}$
$\Rightarrow S=4.5\Omega$