Question

The sensitivity of a voltmeter of 1000 ohms is 1 mV/div When a resistance of 99,000 $\Omega$ is connected in series, its sensitivity becomes :

• A. 1 Volt / div
• B. 10 Volt / div
• C. 1.1 Volt / div
• D. 0.1 Volt / div

Answer 1

The correct option is D 0.1 Volt / div

Given:

Sensitivity of voltmeter = 1mV/div

Resistance of voltmeter $=1000\Omega$

New resistance added in series$=99000\Omega$

Therefore new sensitivity =?

Using,

Sensitivity = $\frac{\text{meter resistance + series resistance}}{\text{full scale reading in volts}}$

$=\frac{R_m+R_s}{E}$

$=\frac{\text{ohms}}{\text{volt}}$

$=\frac{1000+99000}{V\left(fullscale\right)}$ ...... (1)

$V\left(fullscale\right)=\frac{R_m}{\text{sensitivity}}=\frac{1000}{{10}^{-3}}$

$V={10}^6$

From equation (1)

Therefore sensitivity (new)$=\frac{1000+99000}{{10}^6}$

$=0.1$ Volt/div.