Question

By supplying constant current, the deflection in a moving coil galvanometer falls from 50 to 10 divisions when a shunt of 12 is connected across it. The resistance of the galvanometer coil is

Answer 1

let galvanometers resisitance be x ohm

x/xII12=50/10

=12+x/12=5

x=48ohm

Answer 2

Answer:

The correct answer is 48Ω.

Explanation:

Let the constant current is i.

Let the value of 0ne division in a moving coil galvanometer is y.

Before the shunt is connected across the moving coil galvanometer, the galvanometer shows deflection of 50 divisions.

Then,

i = number of divisions × y

 = 50×y

 = 50yA

After the shunt is connected across the moving coil galvanometer, the galvanometer shows deflection of 10 divisions.

Then,

The current in the galvanometer,

$i_{g}$ = number of divisions × y

   = 10×y

   = 10yA

The current in the shunt,

$i_{s}=i-i_{g}$

$i_{s}=50y-10y$

$i_{s}=$40yA

Then,

The voltage across the shunt = the voltage across the galvanometer

$i_{s}R_{s} =i_{g}R_{g}$

40y×12 = 10y×$R_{g}$

$R_{g} =$ 48Ω

So, the resistance of the galvanometer coil is 48Ω.