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=2π3×r         r=3l2πNow, as the distance b/w poles = rNew dipole moment = m×r = m×3l2π                                     =m×l×32π                                     =3M2πmol

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A small bar magnet is placed with its north pole facing magnetic north pole.The neutral points are located at distance r from its centre. If magnet isrotated by 1800, neutral point shall be obtained at distance:1.  2r                                         2.  2r3.  2-13r                                  4.  r22

(3)

At neutral point, magnetic field due to the bar magnet is equal to horizontal component of Earth's magentic field.Initially, when bar magnet's north pole faces magnetic north pole of the Earth:2Mr3=HFinally, when the bar magnet is rotated by 1800:Mr'3=H=2Mr3r'=2-13r

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(1)

At axial point: B=μ04π2Mr3At equitorial point (at same distance): B'=μ04πMr3=12μ04π2Mr3=12BAt distance 2r:B'=μ04πM2r3==18μ04πMr3=18B2=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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