Question

The resistance of a galvanometer is $10\Omega$. It gives full-scale deflection when $1mA$ current is passed. The resistance connected in series for converting it into a voltmeter of $2.5V$ will be

• A. $24.9\Omega$
• B. $249\Omega$
• C. $2490\Omega$
• D. $24900\Omega$

Answer 1

The correct option is C $2490\Omega$

The schematic diagram of this voltmeter can be shown as


From the above figure we can say
$2.5V=I(R+10)$
$2.5V=1\times {10}^{-3}\times (R+10)$
$\therefore R=2490\Omega$