Question

A moving coil galvanometer is converted into an ammeter reads up to 0.03A by connecting a shunt of resistance 4r across it and ammeter reads up to 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 shunt is used ?

A. 0.04 A
B. 0.03 A
C. 0.02 A
D. 0.01 A

Answer 1

By equating the expressions for the maximum current a galvanometer can measure when shunted with resistances '4r' and 'r', we deduce that without any shunt, the galvanometer can read a maximum current of 0.02 A, thus option C is correct.

Step-by-step explanation:

The question we are dealing with involves a moving coil galvanometer which has been converted into an ammeter to read different maximum currents by connecting shunts across it. To solve this problem, we'll apply the principles of parallel circuitry and the fact that the total current in the circuit splits between the galvanometer and the shunt according to their resistances.

When the galvanometer is shunted with a resistance of 4r, it reads up to 0.03A. Let's call the galvanometer resistance G and the maximum current it can measure without a shunt as Ig. So, using the formula for parallel resistances, Ig * G = 0.03A * 4r. When the galvanometer is shunted with a resistance of r, it reads up to 0.06A. Similarly, Ig * G = 0.06A * r.

We can equate the two expressions for Ig * G:

• 0.03A * 4r = 0.06A * r

Solving this gives us Ig = 0.02A, which is the maximum current the galvanometer alone can measure without a shunt.

Therefore, the correct answer is C. 0.02 A.