Question

A galvanometer of coil resistance $99\Omega$ is converted into an ammeter using shunt of $1\Omega$ and is connected as shown in Figure - 1. Ammeter reads 3A. If same galvanometer is converted into voltmeter by connecting a $101\Omega$ resistance in series this voltmeter reads $\frac{4}{5}$ of full scale reading as shown in Figure - 2

• A. Internal resistance of cell is $r=1.01\Omega$
• B. Range of ammeter is 5A
• C. Range of voltmeter is 10V
• D. Full scale deflection current of galvanometer is 0.05A

Answer 1

Answer: (A), (B), (C), (D)

Full scale deflection current of galvanometer is 0.05A

By Fig - 1

$\Rightarrow 12=3[2+\frac{99\times 1}{99+1}+r]$
$r=1.01$

By Fig - 2
$\Rightarrow$
$\Rightarrow R_{eq}=\frac{200\times 2}{200+2}+1.01=2.99\Omega$
$i\approx \frac{12}{2.99}\approx 4A$

$\Rightarrow (i-i,)\times 2=200i_1$
$i_1=\frac{4}{101}$
Given is $\frac{4}{5}{i}_{max}=\frac{4}{101}\Rightarrow i_{max}=\frac{5}{101}\approx 0.05A$
$i_{max}$ is maximum current through galvanometer. Range of voltmeter is $V_{max}=i_{max}\times R=0.05\times 200=10V$


$\Rightarrow 99\times 0.05=i\times 1\Rightarrow i\approx 5A$