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In a Wheatstone bridge circuit, the galvanometer reading is zero (balanced condition). The bridge has resistors P = 10 ohm, Q = 100 ohm, R = 20 ohm, and an unknown resistor S = x. If the internal resistance of all cells is negligible, find the value of x.

1. 10 ohm
2. 100 ohm
3. 200 ohm
4. 500 ohm

Correct answer: 200 ohm

Solution

For a balanced Wheatstone bridge: P/Q = R/S. Given P = 10, Q = 100, R = 20, S = x: 10/100 = 20/x => x = 20 * 100/10 = 200 ohm. The galvanometer reads zero when this condition is satisfied, confirming x = 200 ohm.

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