Question

The current flowing through a coil of resistance $900\Omega$ is to be reduced by 90%. What value of shunt should be connected across the coil.

• A. $90\Omega$
• B. $100\Omega$
• C. $9\Omega$
• D. $10\Omega$

Answer 1

The correct option is B $100\Omega$

We know that,

$\begin{array}{c}I=\frac{V}{R}\\ \therefore \frac{I_1}{I_2}=\frac{R_2}{R_1}\\ R_1=900\Omega \end{array}$

Current flowing through $900\Omega$ resistance is reduced by $90$%

$\therefore$ Current ratio $=10$%:$90$%

$=1:9$

$\begin{array}{c}\therefore \frac{1}{9}=\frac{R_2}{R_1}\\ \Rightarrow \frac{1}{9}=\frac{R_2}{900}\\ \Rightarrow R_2=\frac{900}{9}=100\\ \therefore R_2=shunt=100\Omega \end{array}$

Hence, Option $B$ is correct.