Question

A micrometer has a resistance of 100$\Omega$ and full scale deflection current of $50\mu A$ . How can it be made to work as an ammeter of range 5 mA ?

• A. $1\Omega$
• B. $2\Omega$
• C. $3\Omega$
• D. $4\Omega$

Answer 1

The correct option is A $1\Omega$

Given : $G=100$ $\Omega$ $I_g=50\times {10}^{-6}$ A $I=0.005$ A

Using $I_{g}G=I^{\prime }R$ $⟹$ $I_{g}G=(I-I_g)R$

OR $50\times {10}^{-6}\times 100=(0.005-50\times {10}^{-6})R$ $⟹R=1\Omega$

Thus a galvanometer is converted into an ammeter by connecting it parrallel to a resistance of $1\Omega$.