Question

We know that Ammeter is a device in which a galvanometer & shunt resistor is connected in parallel. Suppose its mentioned in a question that internal resistance is X ohm, current capacity is Y mA, determine the value of resistance needed. Here what is the internal resistance & resistance needed- shunt / galvanometer? Again what is current capacity, current flowing through shunt/galvanometer

Answer 1

Answer:

A galvanometer of 100 resistance gives full scale deflection with 0.01A current

To find the resistance that should be connected convert it into an ammeter of range 10A

Solution:

Galvanometer is a very sensitive instrument therefore it cannot measure heavy currents. In order to convert a Galvanometer into an Ammeter, a very low shunt resistance is connected in parallel to Galvanometer. Value of shunt is so adjusted that most of the current passes through the shunt.

If resistance of galvanometer is R

g

and it gives full-scale deflection when current I

g

is passed through it. Then,

V=I

g

R

g

⟹V=0.01A×100Ω

⟹V=1V

Let a shunt of resistance (R

s

) is connected in parallel to galvanometer. If total current through the circuit is I.

I=10A=I

s

+I

g

V=I

s

R

s

=(I−I

g

)R

s

(I−I

g

)R

s

=I

g

R

g

(10−0.01)R

s

=100×0.01

⟹R

s

=0.1Ω

is the resistance that should be connected in parallel to convert it into an ammeter of range 10A