NEETprep Bank NEET Physics Magnetism and Matter Questions Solved


A bar magnet of length l and magnetic dipole moment M is bent to form an arc which subtends an angle of 120° at centre. The new magnetic dipole moment will be

1.  3M2π

2.  33M2π

3.  3Mπ

4.  2Mπ

                          

Initial dipole moment = m=m.l  m=pole strength      arc=angle×radius         l=π3×r         r=3lπNow, as the distance b/w poles = rNew dipole moment = m×r = m×3lπ                                     =m×l×3π                                     =3mπ

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(1)

B=μ04π2Mr3B'=μ04πM8r3B'=B16

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The magnetic field at a point x on the axis of a small bar magnet is equal to the field at a point y on the equator of the same magnet. The ratio of the distances of x and y from the centre of the magnet is
(a) 2-3

(b) 2-13

(c) 23

(d) 213

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