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NEET-XII-Physics

05: Magnetism And Matter

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  • #7
    A bar magnet of magnetic moment 1.5 J T-1 lies aligned with the direction of a uniform magnetic field of 0.22 T.
    (a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment: (a) normal to the field direction, (a) opposite to the field direction?
    (b) What is the torque on the magnet in cases (i) and (ii)?
    (a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment: (a) normal to the field direction, (a) opposite to the field direction?
    (b) What is the torque on the magnet in cases (i) and (ii)?
    Ans : null (a) Magnetic moment, M = 1.5 J T-1

    Magnetic field strength, B = 0.22 T
    (a) Initial angle between the axis and the magnetic field, θ1 = 0°

    Final angle between the axis and the magnetic field, θ2 = 90°

    The work required to make the magnetic moment normal to the direction of magnetic field is given as:


    (a) Initial angle between the axis and the magnetic field, θ1 = 0°

    Final angle between the axis and the magnetic field, θ2 = 180°

    The work required to make the magnetic moment opposite to the direction of magnetic field is given as:


    (b) For case (i):

    ∴Torque,



    For case (ii):

    ∴Torque,


    (a) Magnetic moment, M = 1.5 J T-1

    Magnetic field strength, B = 0.22 T
    (a) Initial angle between the axis and the magnetic field, θ1 = 0°

    Final angle between the axis and the magnetic field, θ2 = 90°

    The work required to make the magnetic moment normal to the direction of magnetic field is given as:


    (a) Initial angle between the axis and the magnetic field, θ1 = 0°

    Final angle between the axis and the magnetic field, θ2 = 180°

    The work required to make the magnetic moment opposite to the direction of magnetic field is given as:


    (b) For case (i):

    ∴Torque,



    For case (ii):

    ∴Torque,


  • #7-a
    What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment:
    Ans : Magnetic moment, M = 1.5 J T-1

    Magnetic field strength, B = 0.22 T
  • #7-a-i
    normal to the field direction,
    Ans : Initial angle between the axis and the magnetic field, θ1 = 0°

    Final angle between the axis and the magnetic field, θ2 = 90°

    The work required to make the magnetic moment normal to the direction of magnetic field is given as:


  • #7-a-ii
    opposite to the field direction?
    Ans : Initial angle between the axis and the magnetic field, θ1 = 0°

    Final angle between the axis and the magnetic field, θ2 = 180°

    The work required to make the magnetic moment opposite to the direction of magnetic field is given as:


  • #7-b
    What is the torque on the magnet in cases (i) and (ii)?
    Ans : For case (i):

    ∴Torque,



    For case (ii):

    ∴Torque,