Question 26

A galvanometer having a coil of resistance 30Ω need 20 mA of current for full-scale deflection. If a maximum current of 3 A is to be measured using this galvanometer, the resistance of the shunt to be added to the galvanometer should be $$\frac{30}{X}$$Ω.where X is Options

We need to find the shunt resistance for a galvanometer.

G = 30 Ω, $$I_g$$ = 20 mA = 0.02 A, I = 3 A

$$S = \frac{GI_g}{I - I_g} = \frac{30 \times 0.02}{3 - 0.02} = \frac{0.6}{2.98} = \frac{60}{298} = \frac{30}{149}$$

So $$S = \frac{30}{149}$$ Ω, meaning X = 149.

The correct answer is Option 2: 149.

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