Question

A microammeter has a resistance of $100\, \Omega$ and full scale range of $50 \, \mu A$. It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resistance combination-

• A. $50\, V$ range with $10 \,k \Omega$ resistance in series
• B. $10\, V$ range with $200 \,k \Omega$ resistance in series
• C. $10\, m A$ range with $1\, k \Omega$ resistance in parallel
• D. $10\, mA$ range with $0.1\, k \Omega$ resistance in parallel

Answer 1

Answer: (B)

$i_g=i\left(\frac{S G}{S+G}\right)$
or $50 \times 10^{-6}=i\left(\frac{S}{S+100}\right)$....(i)
Also $ V=i_g\left(G+R_0\right)$
or $V=50 \times 10^{-6}\left(100+R_0\right)$ ....(ii)
On simplifying above equations, we get
$V=10 V, R_0=200 \times 10^{-3} \Omega$