Question

The magnetic field at the centre of a circular coil of radius r carrying current I is B1. The field at the centre of another coil of radius 2r carrying same current I is B2. The ratio B1/B2 is?

Answer 1

Magnetic field is inversely proportional to the 3rd power of the radius of the coil
So B1/B2=1/r3/1/8r3
B1/B2=8/1
B1:B2=8:1

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Answer 2

Answer:

8:1

Explanation:

A magnetic field is inversely proportional to the r3 of the radius of the coil

So B1/B2=(1/r3)/(1/(r/2)3)

B1/B2=8/1

B1:B2=8:1