Question

A DC ammeter has a resistance of $0.1\Omega$ and its current range is $0-100A$. If the range is to be extended to $0-500A$, then meter requires the following shunt resistance

• A. $0.010\Omega$
• B. $0.011\Omega$
• C. $0.025\Omega$
• D. $1.0\Omega$

Answer 1

The correct option is C $0.025\Omega$


$I_m\text{=Full scale deflection current=100 A}$
$\text{I= Current to be measured=500 A}$

$\text{Multiplying power,}$

$\frac{I}{I_m}=\frac{500}{100}=5$

$R_m=0.1\Omega$

$I_m=\frac{I{R}_{sh}}{R_{sh+R_m}}$

$\Rightarrow m=1+\frac{R_m}{R_{sh}}$

$\Rightarrow R_{sh}=\frac{R_m}{m-1}=\frac{0.1}{5-1}=0.025\Omega$