Question

The resistance of an ammeter is $13\Omega$ and its scale is graduated for a current upto $100A$. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto $750$A by this meter. The value of shunt resistance is

• A. $20\Omega$
• B. $2\Omega$
• C. $0.2\Omega$
• D. $2K\Omega$

Answer 1

Answer: (B)

$2\Omega$

Given: $R_A=13\Omega$

Let the shunt resistance be $R_s$

Current flowing through $R_A$ is $I_1=100A$

$\therefore$ Current flowing through the shunt resistance, $I_2=750-I_1=750-100=650A$

Potential difference across point P and Q is same for the two segments.

$\therefore$ $I_2\times R_s=I_1\times R_A$

$650\times R_s=100\times 13$

$⟹R_s=2\Omega$