Question

A MCG has a current sensitivity of 5 div/mA and a voltage sensitivity of 2 div/mV and a FSD of
200 div. It will work as
(1) an ammeter of range 40A
(2) an voltmeter of range 0.1V
(3) an ammeter of range 4mA
(4) an voltmeter of range 100 V​

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