AP EAPCET 08-Jul-2022 Shift 1 Paper

The given situation is shown below.

Note Earth's field goes from South to North: At neutral point horizontal component of earth, is opposed by field of magnet so, at neutral point,
BH=Bmagnet
⇒ BH=

µ0

4π

.

M

r3

Where,
M= magnetic dipole moment of magnet and
r= distance of neutral point from centre of magnet
Here, BH=3.2×10−5T
r−6cm=6×10−2m
Hence, 3.2×10−5=10−7×

M

(6×10−2)3

⇒ M=

3.2×10−5×216×10−6

10−7

=6.×10−2A−m2
If length of magnet is taken 2l, then
M=m.2l, (∵ m= pole strength)
Here, 2l=16cm=16×10−2m
⇒ 6.9×10−2=m×16×10−2
⇒ m=

6.9

16

=0.43A−m≃0.5A−m