Question

A current passing through a circular coil of two turns produces a magnetic field of 8 T at its centre. The coil is then rewound, so as to have four turns and current is passed through it is doubled. Now magnetic field at the centre of the coil will be a) 64 T c) 16 T b) 32 T d) 8 T​

Answer 1

Explanation:

B=

4π

μ

0

r

2πnI

i.e. B∝

r

n

;

Given, L=2πr

1

×2=2πr

2

×4;

r

2

r

1

=

2

4

=2

B

1

B

2

=

n

1

n

2

×

r

2

r

1

=

2

4

×2=4

or B

2

=4B

1

=4B

Answer 2

Answer:

B=4πμ0r2πnI i.e. B∝rn;

Given, L=2πr1×2=2πr2×4;r2r1=24=2

B1B2=n1n2×r2r1=24×2=4 

or B2=4B1=4B