NEET Physics Magnetism and Matter Questions Solved

NEET - 2016


A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60 is W. Now the torque required to keep the magnet in this new position is

(a) W3                    (b) 3W

(c) 3W2                (d) 2W3

Concept Videos :-

#3 | Magnetic Dipole Moment & Field due to Bar Magnet
#4 | Superposition of Magnetic Field due to Bar Magnet
#5 | Field due to Short Bar Magnet
#6 | Torque Acting on Bar Magnet in Uniform Field
#7 | Work Done in Rotating Dipole in Field & PE
#8 | Oscillations of Bar Magnet in Uniform Field
#9 | Solenoid as Equivalent Bar Magnet

Concept Questions :-


(b) Work done is rotating the magnet 

            W=MBcos θ0-cos θ

Where, M= magnetic moment of the magnet

           B = Magnetic field 

           W = MB cos o° - cos 60°

           W =1-12MB2

    MB=2W                        ...(i)

Torque on a magnet in this position is given by,

 π=M×B= MB sin θ=2W sin 60 [from Eq. (i)]


Difficulty Level:

  • 8%
  • 60%
  • 25%
  • 9%
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