Question

A long straight wire of radius a carries a
steady current I. The current is uniformly
distributed over its cross-section. The ratio
of the magnetic fields B and B’, at radial
distances a/2 and 2a respectively, from the
axis of the wire is
(a) 1 (6) 4 ​

Answer 1

Answer:

B.dL=μ

0

I

enclosed

For the smaller loop,

⇒B×2π

2

a

=μ

0

×

πa

2

1

×(

2

a

)

2

=μ

0

I×

4

1

=

4

μ

0

I

⇒B

1

=

4πa

μ

0

I

B

′

×2π(2a)=μ

0

I

B

′

B

=

4πa

μ

0

I

×

μ

0

I

4πa

=1

Answer 2

Here's your answer in the given attachment :-

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