Q. 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’s needed to be connected in series with the coil will be
A) $10^{3}$
B) $10^{5}$
C) 99995
D) 9995
Explanation
(d) Full scale deflection current
$= \frac{150}{10}mA = 15mA$
Full scale deflection voltage
$= \frac{150}{2}mV = 75mV$
Galvanometer resistance
$G = \frac{75mV}{15mA} = 5\Omega$
Required full scale deflection voltage.
$V = \ 1\ \times \ 150 = \ 150\ volt$
Let resistance to be connected in series is R.
$\Longrightarrow \ \ V = I_{g}(R + G)$
$\therefore 150 = 15 \times 10^{- 3}(R + 5)$
$\Longrightarrow 10^{4} = R + 5$
$\Longrightarrow R = 10000 - 5 = 9995$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.