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A galvanometer of resistance 20 ohm gives a full-scale deflection when 0.2 V is applied across it. To convert it into an ammeter reading up to 10 A, what should be done?

1. connect a 0.02 ohm resistor across it (in parallel)
2. connect a 0.01 ohm resistor across it (in parallel)
3. connect a 200 ohm resistor in series with it
4. connect a 2000 ohm resistor in series with it

Correct answer: connect a 0.02 ohm resistor across it (in parallel)

Solution

Ig = 0.2/20 = 0.01 A; the shunt S = Ig*G/(I - Ig) = (0.01*20)/(10 - 0.01) approx 0.02 ohm, connected in parallel.

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