A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10 divisions per milliampere and voltage sensitivity is 2 divisions per millivolt. In order that each division reads 1V the resistance in ohm needed to be connected in series with the coil will be :
Answer & explanation
Correct answer: option 2
Voltage sensitivity = $\frac{\text { Current sensitivity }}{\text { Resistance of galvanometer G}}$
G = $\frac{\text { Current sensitivity }}{\text { Voltage sensitivity }}$
G = $\frac{10}{2}=5 \Omega$
Full scale deflection current, $i_{g}=\frac{150}{10}=15 mA$
Voltage to be measured, V = $iR=150 \times 1=150 V$
Hence, $\mathrm{R}=\frac{V}{i_{g}}-G=\frac{150}{15 \times 10^{-3}}-5=9995 \Omega$