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In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is G, the resistance of ammeter will be:

1. 1 / 499 G
2. 499 / 500 G
3. 1 / 500 G
4. 500 / 499 G

Correct answer: 499 / 500 G

Solution

In an ammeter, the shunt resistance is connected in parallel with the galvanometer to allow most of the current to bypass the galvanometer. If 0.2% of the current passes through the galvanometer, the shunt resistance is much smaller than the galvanometer resistance. Using the formula for parallel resistances, the effective resistance of the ammeter is approximately (499/500)G.

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