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Title: Magnetism notes
Description: This note covers all the necessary topics, equations and definitions in easy and simple language.
Description: This note covers all the necessary topics, equations and definitions in easy and simple language.
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MAGNETISM
The word magnet is derived from the iron core magnetite found near the ancient city of Magnesia
(modern Turkey)
...
It is a mineral called magnetite (Fe 3O4)
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It is a heavy, hard, black or dark grey in color
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1
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2
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3
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For an electric dipole, electric intensity is given by,
πΈ=
2π
4π±π0 π₯ 3
β¦Equation 2
(where p = electric dipole moment)
5
...
Also, we know that magnetic induction along the axis of a short bar magnet is given by,
π΅=
π0 2π
4π± π₯ 3
7
...
Also, when a short bar magnet is placed in an external magnetic field, it
ββ x π΅
β
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magnetic field is given by π = π
Hence, we can say that, a circular coil carrying current behaves as a magnetic dipole
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Consider an electron revolving in a Bohrβs orbit having radius r, with velocity v
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Let e be the charge of an electron and π0 be the mass of the electron
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i
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Current is given by, I=
iii
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h
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β’ The Gyromagnetic ration of an orbital electron
The gyromagnetic ratio is defined as the ratio of orbital magnetic moment and the orbital angular
momentum of an electron in an atom
...
E = S+O
ππ§ =
ππππ‘
π
ππ§ πΌ
π΅ππ₯π‘
π
,
ππ§ =
πΆπππ₯π‘
π
[L-1 I-1]
Unit = A/m
β’ Magnetic Intensity
It is defined as the ration of magnetic induction to the permeability of the medium
H=
π΅
π
[L-1I]
Unit=A/m
For a toroid, H is given by,
H = πI
H=
π
2π±π
πΌ
[n=no of turns per unit volume]
β’ Magnetic susceptibility of a medium
It is defined as magnetization per unit magnetic intensity
...
[It is equal to the fractional charge in the magnetic induction due to the medium]
Relation between permeability & magnetic susceptibility of a medium
π = π0 (1 + ππ)
ii
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Without iron ore
π΅0 =
ii
...
1
]
With iron ore
π΅ = π΅0 + π΅π
(π΅π β magnetic field contributed by iron ore)
π΅π πΌ ππ§
π΅π = π0 ππ§
π΅=π0H + π0 ππ§
β΅ππ§
= ππH
π΅=π0H + π0ππH
(π0 is proportionality constant)
π΅=π0H(1 + ππ)
(β΅ 1 + ππ = ππ )
π΅=π0ππ π»
[β΅ππ =
β΄
π
ππ
] ( π = ππ π π0 )
π΅ = ππ»
β’ Diamagnetism/Diamagnetic substances
Substances having atoms or molecules of xero magnetic moment and which are weakly repelled by a
magnet are called Dia-magnetic substances
...
g
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Properties
β
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They lose their magnetism on removal of external magnetic field
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5
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6
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1
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3
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β’ Para-magnetism/Para-magnetic substance
Substances having atoms or molecules of non-zero or finite magnetic moment and which are really
weakly attracted by a magnet are called para-magnetic substances
...
g
...
Properties
β
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Weakly magnetized in the direction of the external magnetic induction π΅
2
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3
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4
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5
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6
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7
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β’ Ferromagnetism
Substances having atom or molecules of non-zero or finite magnetic moment and which are strongly
attracted by a magnet are called ferromagnetic substances
...
g
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Properties
1
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2
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If placed in a non-uniform magnetic field, a ferromagnetic substance tents to move from the
weaker part to the stronger part of the magnetic field
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The susceptibility is positive and very high
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If a thin rod of ferromagnetic substance is kept between two conical pole pieces of an
electromagnet it comes to rest with its axis parallel to the magnetic induction between the
poles
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All the atoms of the ferromagnetic materials have a resultant magnetic moment even in the
absence of external magnetic field
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If a paramagnetic material at an absolute temperature T is places in an external magnetic field of
β ext the magnitude of its magnetization is,
induction π΅
π΅β π₯π‘
π
π΅β π₯π‘
β΄ ππ§ = πΆ
π
ππ§ πΌ
Where the proportionality constant C is called Curie constant
...
*Note
1
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2
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5 tesla per
kelvin
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The region in which all magnetic moments are aligned in the same direction are known as
domains
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If a ferromagnetic material is placed in an external magnetic field, the magnetic domains may
increase of decrease in size
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Above the curie temperature, a ferromagnetic substance is converted into a paramagnetic substance
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Weakly repelled from the region of strong field
when placed in a non-uniform magnetic field
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ππ is small, negative and very nearly
temperature independent
...
Paramagnetic Material
Atoms posses a net magnetic moment that are all
randomly directed in the absence of an external
magnetic field
...
It gets weakly magnetized in the same direction
as that of the field
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π r is slightly greater than 1 & decreases with
increasing temperature
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It gets weakly magnetized when placed in an
external magnetic field
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The permanent atomic magnetic moments of a
ferromagnetic material interact strongly through
exchange interaction forming domains which are
spontaneously magnetized to saturation
...
It retains some magnetization even after the
external magnetic field is removed
...
Ferromagnetic Material
ππ & π are positive & very high
...
It retains some magnetization even after the
external magnetic field is removed
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Its magnetization becomes zero when the
external magnetic field is removed
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ππ is small & negative, π r is slightly less than 1
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The most exotic diamagnetic substances are superconductors
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The
phenomenon of perfect diamagnetism is superconductors is called Meissner effect
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Diamagnetic substances are universal
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But it is weak and hard to
detect if the substance is paramagnetic or ferromagnetic
...
If a watch glass containing a small quantity of diamagnetic liquid is placed on two dissimilar
magnetic poles, the liquid shows on two dissimilar magnetic poles, the liquid shows elevation in
the middle, whereas if the liquid is paramagnetic it shows depression in the middle
...
Depending on the structure & type of ferromagnetic material, the volumes of the magnetic
domains vary from about 10-18 to 10-12 m3 so each domain may contain roughly 1017 to 1021
atoms
...
Boundaries between regions in which domains have different orientations are called domain
walls (thickness 1000 Γ approx
...
The magnetic dipole moments of the domain rotate so as to align with the applied magnetic
field
...
This effect is responsible for producing a net magnetic dipole
moment when the applied magnetic field is strong
...
Title: Magnetism notes
Description: This note covers all the necessary topics, equations and definitions in easy and simple language.
Description: This note covers all the necessary topics, equations and definitions in easy and simple language.