Current Electricity and Electrical InstrumentHard
Question
A moving coil galvanometer is converted into an ammeter reads upto 0.03 A by connecting a shut of resistance 4r across it and ammeter reads upto 0.06 A, when a shunt of resistance r is used. What is the maximum current which can be sent through this galvanometer if no shut is used?
Options
A.0.04 A
B.0.03 A
C.0.02 A
D.0.01 A
Solution
Let R be the resistance of the ammeter & I be the maximum current passing through the ammeter.
In the first case 0.03A is main current and in the second case 0.06 A is main current.
for Ist case
for second case 
R + 4r = 2R + 2r ⇒ R = 2r
The value of
= 0.02 A
This is the maximum value of current in ammeter.
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