Question

A galvanometer of resistance 100 ohm gives full scale deflection with 5 millampere current. To convert it into a 5 volt range voltmeter, the value of resistance connected in series is :

• A. 900 $\Omega$
  
• B. 9999 $\Omega$
• C. 10000 $\Omega$
• D. 1 $M\Omega$

Answer 1

The correct option is A 900 $\Omega$

Let resistance x be connected in series,
= $\frac{V_1}{V_2}=\frac{R_1}{Req}=\frac{R_1}{R_1+x}$
$\frac{5\times {10}^{-3}\times 100}{5}=\frac{100}{100+x}$ $[\because V=iR]$

$100+x=1000$
$x=900\Omega$