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A wire carries a current. Maintaining the same current it is bent first to form a circular plane coil of one turn which produces a magnetic field B at the centre of the coil. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre of the double loop, caused by the same current is
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- 4B
- B/4
- B/2
- 2B
Correct Option: A
Let I be current and l be the length of the wire.
| For Ist case : B = | = | where 2πr' = l and n = 1 | ||
| 2R | l |
| For IInd Case : l = 2(2πr') ⇒ r' = | |
| 4π |
| B' = | = | = | = 4B | ||||
| 2r' | 2 | l | |||||
| 4π |
