IIT JEE , AIEEE Forum - Physics , Magnetism

krishna.gopal

Hi vpy, symetry suggests that at any point there will be no component of field perpendicular to plane or along the direction of current. So the field will be parallel to plane but perpendicular to direction of current. Suppose i want to find field at a distance x from the plane. Make a rectangular loop of sides l and 2x such that plane cuts the 2x sides in between. Now_{[ ]}

^{[ ]} B.dl on 2x sides will be zer (Field and path are perpendicular). So _{[ ]}

^{[ ]} B.dl=B*2l=2Bl (as direction of field on two sides will be opposite)
2Bl=

_oil
So B =

_oi/2.

This will be independent of distance from the plane.

(b) If current density is i and -i. The field will be vector sum of two fields. For oints in between the planes the two fields add up and hence field is

_oi. For other points they cancel each other and hence field is zero

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