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If the bar magnet in exercise 5.13 is turned around by 180º, where will the new null points be located?

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Class 12 Physics
CBSE and UP Board
Magnetism and Matter
Chapter-5 Exercise 5.14

NCERT Solutions for Class 12 Physics Chapter 5 Question 14

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1 Answer

  1. The magnetic field on the axis of the magnet at a distance d₁= 14 cm, can be written as:

    B₁ = μ0 /4π x [2M/(d₁)³] =H   ———–Eq 1

    Where, M = Magnetic moment

    μ0= Permeability of free space,

    H = Horizontal component of the magnetic field at d₁.

    If the bar magnet is turned through 180°, then the neutral point will lie on the equatorial line.

    Hence, the magnetic field at a distance d₂, on the equatorial line of the magnet can be written as:

    B₂ = μ0 /4π x [2M/(d₂)³] =H   ———–Eq 2

    Equating equations (1) and (2), we get:

    2/(d₁)³= 1/(d₂)³

    => (d₂/d₁)³ = 1/2

    => d₂  =  d₁ x (1/2)1/3

    => d₂  = 14 x 0.794 = 11.1 cm

    The new null points will be located 11.1 cm on the normal bisector.

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