Question

Resistance in the two gaps of a meter bridge are 10 ohm and 30 ohm respectively. If the resistances are interchanged the balance point shifts by :-

• A. 33.3 cm
• B. 66.67 cm
• C. 25 cm
• D. 50 cm

Answer 1

The correct option is D 50 cm

In first case: $R=10\Omega$ and $S=30\Omega$
In balanced condition, $\frac{R}{S}=\frac{l}{100-l}$ or $\frac{10}{30}=\frac{l}{100-l}$
or $3l=100-l$ or $4l=100\Rightarrow l=l_1=25$ cm
In 2 nd case: $R=30\Omega$ and $S=10\Omega$
In balanced condition, $\frac{R}{S}=\frac{l}{100-l}$ or $\frac{30}{10}=\frac{l}{100-l}$
or $l=300-3l$ or $4l=300\Rightarrow l=l_{=}75$ cm
The shifts $=l_2-l_1=75-25=50$ cm