Question

A galvanometer having a coil resistance of 100 $\Omega$ gives a full scale deflection when a current of 1 mA is passed through it. The value of the resistance which can convert this galvanometer into ammeter giving a full scale deflection for a current of 10 A, is

• A. 0.01 $\Omega$
• B. 2 $\Omega$
• C. 0.1 $\Omega$
• D. 3 $\Omega$

Answer 1

Answer: (A)

0.01 $\Omega$

When full-scale current is flowing, potential difference,

$V={10}^{-3}\times 100=0.1V$

Let shunt resistance be $R$. Current flowing through $R$ in full scale reading is $I_{sh}=10-0.001=9.999A$

$V=I_{sh}R$

$0.1=9.999R$

$R\approx 0.01V$