Question

tell me right answer​

Answer 1

Explanation:

ANSWER

Magnetic field on the axis of a circular coil

B1=2(R2+z2)3/2μ0iR2

Magnetic field at the center  of the circular coil:

B2=2Rμ0i

Given, B1=81B2

⇒2(R2+z2)3/2μ0iR2=812Rμ0i

⇒8R3=(R2+z2)3/2

⇒64R6=(R2+z2)3

(4R2)3=(R2+z2)3

⇒4R2=R