Question

A silver voltmeter of resistance 2 $\Omega$ and a 3 $\Omega$ resistor and are connected in series across a cell. If a resistance of 2 $\Omega$ is connected in parallel with the voltmeter, then the rate of deposition of silver

• A. decreases by 25%
• B. increase 25%
• C. increase by 37.5%
• D. decreases by 37.5%

Answer 1

The correct option is D decreases by 37.5%

The rate of deposition of silver in the silver voltmeter is a measure of current through the voltmeter.

Thus we need to find the percentage decrease in current through the voltmeter.

Initially, current through the voltmeter=$\frac{V}{R_{voltmeter}+R_{resistor}}=\frac{V}{5}=i_1$

After connecting resistor in parallel,

current extracted from the cell$=\frac{V}{\frac{\left(2\right)\left(2\right)}{(2+2)}+3}=\frac{V}{4}$

Thus current through the voltmeter $=\frac{V}{8}=i_2$

Thus the percentage decrease in current through the voltmeter $=\frac{i_1-i_2}{i_1}\times 100$%=$37.5$%