Question

When a current of $5 \,mA$ is passed through a galvanometer having a coil of resistance $15 \, \Omega$, it shows full scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a voltmeter of range $0-10 \,V$ is :

• A. $1.985 \times 10^3 \, \Omega$
• B. $2.045 \times 10^3 \, \Omega$
• C. $2.535 \times 10^3 \, \Omega$
• D. $4.005 \times 10^3 \, \Omega$

Answer 1

Answer: (A)

$1.985 \times 10^3 \, \Omega$

Answer 2

$i_g = 5 \times 10^{-3} A$
$G = 15 \, \Omega$
Let series resistance be R.
$V = i_g (R + G)$
$10 = 5 \times 10^{-3} (R + 15)$
$R = 2000 - 15 = 1985 = 1.985 \times 10^3 \, \Omega$