MHT-CET : Physics Entrance Exam

### MHT - CET : Physics - Magnetism Page 1

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1.

Magnetic Dipole and Magnetic Dipole Moment:

• An isolated magnetic monopole does not exist.

• Magnetic Dipole: Magnetic dipole is a system of two poles (North and South) of same polestrength but opposite in nature and separated by some distance (usually denoted by 2l)

• Axis of dipole: The straight line passing through the two poles of a magnetic dipole is called the axis of the dipole.

• Equator of the dipole: The straight line passing through the centre of the dipole and perpendicular to the axis is called the equator of the dipole. (It is a perpendicular bisector.)

• Magnetic Length: The distance 2l between the two poles is called the magnetic length of the dipole.

• Relation between Magnetic length and Geometric length:

Magnetic length =

 5 6

× Geometric length

• Dipole moment: () Magnetic dipole moment is a vector quantity whose magnitude is equal to the product of the strength of any one pole (m) and the magnetic length (2l), and direction is from south pole to north pole.
 = m ´ 2l

Units in SI System:

 Quantity Unit Pole-strength Ampere-metre (A-m) Magnetic dipole moment Ampere-metre2 (A-m2)

2.

Magnetic Induction () at Any Point Due to Short Magnetic Dipole:

Consider a magnetic dipole of dipole moment (). Consider a point P at a distance 'r' from the centre of the dipole making an angle q with the dipole axis as shown in the figure.

Derivation of Magnetic Induction ()

B=

 m0 4p

 M r3

tan
f = tanq

Special Cases:

(i

If P is an axial point, substitute q = 0° or q = 180° in the equation

B=

 m0 4p

 M r3

\ Baxis =

 m0 4p

 2M r3

for an axial point.

(ii)

If P is an equatorial point, substitute q = 90° in the equation

B=

 m0 4p

 M r3

\ Bequator =

 m0 4p

 M r3

for an equatorial point.

Remember: Magnetic induction is a vector quantity.

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