IIT JEE , AIEEE Forum - Physics , Magnetism

Ank999

A long straight wire carries a current i. Let B₁ be the magnetic field at a point P at a distance d from the wire. Consider a section of length l of this wire such that the point P lies on a perpendicular bisector of the section. Let B₂ be the magnetic field at this point due to this section only. Find the value of of d/l so that B₂ differs from B₁ by 1%.

krishna.gopal

B1 = (mu_not)*i/(2*pi*r)

If you solve for field because of finite wire

B2 = ((mu_not)*i/(2*pi*r))*((l/2)/sqrt((l/2)^2+d^2))
for B2 tp be 0.99 B1

l/(2*sqrt((l/2)^2+d^2))=0.99
Sollve to get d/l

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