First slide

Magnetic field due to a current carrying circular ring

Question

A circular coil has one turn and carries a current i. The same wire is wound into a smaller coil of 4 turns and the same current is passed through it. The field at the centre

Easy

A

decreases to 1/4 of the value
B

remains the same
C

increases to 14 times the value
D

increases to 16 times the value

Solution

$B \propto (n / r)$
Here number of turns becomes 4 times while the radius becomes (1/4) times. Hence B becomes 16 times

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