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In a circuit, a 20 V battery is connected such that resistors of 6 ohm, 4 ohm, 8 ohm, and 12 ohm form a Wheatstone-bridge arrangement. An ammeter is connected in the middle (galvanometer) branch. What does the ammeter read?

1. 0 A
2. 1/2 A
3. 1 A
4. 2 A

Correct answer: 0 A

Solution

With arms 6 ohm and 12 ohm in one pair and 4 ohm and 8 ohm in the other pair, the ratios 6/12 = 4/8 = 1/2 satisfy the balance condition, so no current flows through the middle branch and the ammeter reads 0 A.

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