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The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then
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- the resistance and the specific resistance, will both remain unchanged
- the resistance will be doubled and the specific resistance will be halved
- the resistance will be halved and the specific resistance will remain unchanged
- the resistance will be halved and the specific resistance will be doubled
Correct Option: C
| R = | | , now l2 = 2l1 | |
| A1 |
A2 = π(r2)² = π (2r1)² = 4π r1² = 4A1
| ∴ R2 = | ρ (2 l1) | = | ρ l1 | = | R | |
| 4 A1 | 2 A1 | 2 |
∴ Resistance is halved, but specific resistance remains the same.
