Question

A $1\Omega$ voltmeter has a range of $1\text{V}$. Find the additional resistance which has to be joined in series with this voltmeter, to increase the range of the voltmeter to $100\text{V}$.

• A. $10\Omega$
• B. $\frac{1}{99}\Omega$
• C. $99\Omega$
• D. $100\Omega$

Answer 1

The correct option is C $99\Omega$

Range $=\Delta V=i\times R_g$

$\Rightarrow 1=i{R}_g$

Here, $R_g$ is the resistance of the voltmeter, $i.e.1\Omega$.

$\Rightarrow i=1\text{A}$

We have to increase range to $100\text{V}$.

So, let's assume that we have to connect an additional series resistor of resistance $R$.


Then,

$100=i\times (R_g+R)$

$\Rightarrow 100=1\times (1+R)$

$\therefore R=99\Omega$

Hence, option $\left(C\right)$ is the correct answer.