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In a metre-bridge, the balancing length from the left end when standard resistance of 1 Ω is in right gap is found to be 20 cm. The value of unknown resistance is
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- 0.25Ω
- 0.4Ω
- 0.5Ω
- 4Ω
Correct Option: A
Let unknown resistance be X. Then condition of Wheatstone's bridge gives
| X | = | 20r | , where r is resistance of wire per cm. | |
| r | 80r |
| ∴ X = | 20 | x R = | 1 | x 1 = 0.25 Ω |
| 80 | 4 |
