Question

the resistance of a moving coil galvanometer is 20ohm . it require 0.01A current for full scale deflection. Calculate the value of resistance require d to convert it into a voltmeter of range 20volts.​

Answer 1

ANSWER
Given data:
G=20Ω I
g
​
=50×10
−3
A;I=20A,
S=?;V=120V,R=?
Solution:
i) ∴S=G.
I−I
g
​

I
g
​

​
=
20−50×10
−3

20×50×10
−3

​
=
20−0.05
1
​

S=0.05Ω
A shunt of 0.05Ω should be connected in parallel.
ii) R=
Ig
V
​
−G
=
50×10
−3

120
​
−20=2400−20=2380Ω
R=2380Ω.

Answer 2

Answer:

The value of resistance required to convert galvanometer to voltmeter is 1980Ω.

Explanation:

The reading of the voltmeter is given as,

$V=I_g(R+R_g)$            (1)

Where,

V=reading of the voltmeter

Ig=current through the galvanometer

R=required resistance

Rg=resistance of the galvanometer

From the question we have,

V=20volts

Rg=20Ω

Ig=0.01A

By putting the values in equation (1) we get;

$20=0.01(R+20)$

$R+20=\frac{20}{0.01}=2000$

$R=2000-20=1980\Omega$

Hence, the value of resistance required to convert galvanometer to voltmeter is 1980Ω.