Question

What is the value of shunt resistance required to convert a galvanometer of resistance $100$ $\Omega$ into an ammeter of range $1\,A$ ? Given : Full scale deflection of the galvanometer is $5 \,mA$

• A. $\frac{5}{9.95} \Omega$
• B. $\frac{9.95}{5} \Omega$
• C. $0.5\, \Omega$
• D. $0.05 \,\Omega$

Answer 1

Answer: (A)

$\frac{5}{9.95} \Omega$

Answer 2

By conversion of galvanometer into ammeter
$S=\left(\frac{I_{g}}{I-I_{g}}\right) G$
($I_g =$ Current through galvanometer
S = Shunt resistance
G == Galvanometer resistance)
where $I_{g}=5 \times 10^{-3} A$
$I =1 A$
$G =100\, \Omega$
$S =\left(\frac{5 \times 10^{-3}}{1-5 \times 10^{-3}}\right) \times 100$
$=\frac{5 \times 10^{-3} \times 100 \times 10^{3}}{(1000-5)}$
$=\frac{500}{995}=\frac{5}{9.95} \Omega$