Question

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 $1volt$, the resistance in ohms needed to be connected in series with coil will be-

• A. ${10}^5$
• B. ${10}^3$
• C. $9995$
• D. $99995$

Answer 1

Answer: (C)

$9995$

According to the question,

Voltage sensitivity $=\frac{Currentsensitivity}{ResistanceofgalvanometerG}$

$\Rightarrow G=\frac{10}{2}=5\Omega$.

Here $i_g$= Full scale deflection current $=\frac{150}{10}=15mA$

$V=$ Voltage to be measured $=150\times 1=150V$.

Hence $R=\frac{V}{i_g}-G=\frac{150}{15\times {10}^{-3}}-5=9995\Omega$.