Question

, The magnetic field on the axis of a short bar magnet
at a distance of 10 cm is 0.2 oersted. What will be
the field at a point, distant 5 cm on the line
perpendicular to the axis and passing through the
magnet?
(a) 0.025 oersted
(b) 0.2 oersted
(c) 0.4 oersted
(d) 0.8 oersted

Answer 1

Answer:

Consider a point P located on the axial line of a short bar magnet of magnetic length 2l and strength M. Let us find B at a point P which is at a distance z from the centre of magnet.

Magnetic flux density of P due to N-pole is

B1=μ04π(M(z−l)2) along NP

Similariy on S-Pole

B2=μ04π(M(z−l)2) along SP

Net magnetic flux at Pis

B=B1−B2=μ04π[M(z−l)2−M(z+l)2]

=μ04π[4Mdl(z2−l2)2]

=μ04π[M×2l(z2−l2)22z]

B=μ04π2Mz(z2−l2)2

B=μ04π.3Mdz2(∵z>>l2)

∴B=μ04π2Mz3M^

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