Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic fields such as electric fields, magnetic fields, and light, and is one of the four fundamental interactions (commonly called forces) in nature. The other three fundamental interactions are the strong interaction, the weak interaction, and gravitation.[1] At high energy the weak force and electromagnetic force are unified as a single electroweak force.

1. UNIT-2
ELECTROMAGNETISM

2. Which electrical Appliances Use
Magnets?
• Motors(spinning motors, sewing machine ,fan, water pumps etc. )
• Transformers
• Hair dryers
• Food mixers
• Microwaves
• Refrigerators
A magnet is a material or object that produces a magnetic field. This magnetic field is
invisible but is responsible for the most notable property of a magnet: a force that
pulls on other ferromagnetic materials, such as iron, and attracts or repels other
magnets.
 Lodestone is naturally available magnet.

3. Magnetism
A material is said to be magnetized if it displaces the following properties.
1. When suspended freely it comes to rest in a line running approximately earth’s
north and south.
 The north pole of a magnet is the pole that, when the magnet is freely
suspended, points towards the Earth's North Magnetic Pole(actual magnetic
south pole of earth) which is located in northern Canada.
 Earth’s South magnetic pole(actual magnetic north pole earth) is located in
Antarctica.

4. 2. It is able to impart magnetism to other magnetic materials
 Diamagnetic materials are slightly repelled by a magnetic field and the material
does not retain the magnetic properties when the external field is removed.
Examples: copper, silver, and gold etc.
 Paramagnetic materials are slightly attracted by a magnetic field and the
material does not retain the magnetic properties when the external field is
removed.
Examples: magnesium, molybdenum, lithium, etc.
 Ferromagnetic materials exhibit a strong attraction to magnetic fields and are
able to retain their magnetic properties after the external field has been
removed.
Examples: nickel, iron, cobalt etc.
3. It exerts a force on other magnetic material

5. Permanent Magnets and
Electromagnets
• A permanent magnet is an object made from a
ferromagnetic material that is magnetized and
creates its own persistent magnetic field.
• An electromagnet is made from a coil of wire
which acts as a magnet when an electric current
passes through it.
 Often an electromagnet is wrapped around a
core of ferromagnetic material like steel, which
enhances the magnetic field produced by the coil.

6. Permanent Magnet vs. Electromagnet
• Magnetic Properties
1. A permanent magnet’s magnetic properties exist when the magnet is
magnetized. An electromagnetic magnet only displays magnetic properties when
an electric current is applied to it.
2.The magnets that you have affixed to your refrigerator are permanent magnets,
while electromagnets are the principle behind AC motors.
• Magnetic Strength
1.Permanent magnet strength depends upon the material used in its creation.
2. The strength of an electromagnet can be adjusted by the amount of electric
current allowed to flow into it.
3. As a result, the same electromagnet can be adjusted for different strength levels.

7. • Loss of Magnetic Properties
1. If a permanent magnet loses its magnetic properties, it will be rendered useless
and its magnetic properties can be only recovered by re-magnetizing.
2. An electromagnet loses its magnetic power every time an electric current is
removed and becomes magnetic once again when the electric field is introduced
• Advantages
1. The main advantage of a permanent magnet over an electromagnet is that a
permanent magnet does not require a continuous supply of electrical energy to
maintain its magnetic field.
2. An electromagnet’s magnetic field can be rapidly manipulated over a wide range
by controlling the amount of electric current supplied to the electromagnet.

8. Magnetic effect of an electric current
HISTORY:
• On 21 April 1820, Hans Christian Orsted noticed a compass needle
deflected from magnetic north when the electric current from the battery
he was using was switched on and off.
• This deflection convinced him that magnetic fields radiate from all sides of
a wire carrying an electric current

9. Cross and dot conventions

10. Right hand thumb rule
• An electric current passes through a straight wire.
Here, the thumb points in the direction of the
conventional current (from positive to negative), and
the fingers point in the direction of the magnetic
lines of flux.

11. Maxwell’s cork screw rule
• The direction of rotation of a right-handed
cork-screw screwed into the conductor in the
direction of current flow indicates the
direction of the lines of magnetic flux around
the conductor.

12. Right hand grip rule
• An electric current passes through a solenoid, resulting in a
magnetic field.
• When you wrap your right hand around the solenoid with
your fingers in the direction of the conventional current, your
thumb points in the direction of the magnetic north pole.

13. Nature of magnetic field of long
straight conductors
• The nature of the magnetic field lines around a straight
current carrying conductor is concentric circles with centre at
the axis of the conductor.
• The strength of the magnetic field created
depends on the current through the conductor.
• The strength of the field was strongest next
to the wire and diminished with distance from
the conductor until it could no longer be
detected.
• The direction of the magnetic field was dependent on the
direction of the electrical current in the wire.

14. Nature of magnetic field of solenoid
• A solenoid is a coil wound into a tightly packed helix.
• A magnetic field develops
that flows through the center
of the loop or coil along its
longitudinal axis.
• The magnetic field circling
each loop of wire combines
with the fields from the other
loops to produce a concentrated field down the center of the
coil.
• The strength of a coil's magnetic field increases not only with
increasing current but also with each loop that is added to the
coil.
• The concentrated magnetic field inside a coil is stronger than
the field outside the coil.

15. Nature of magnetic field of toroid
• A toroidal coil is a group of current loops on a surface
of a torus, that have the same current
passing through.
• Because of symmetry the magnetic field
strength is constant in the constant
distance from the center of the torus.
• If the radius of the current loop is small compared to
the toroid radius, the magnetic field is constant.
• The magnetic field outside the toroid is negligible.

16. MAGNETIC FIELD/MAGENTIC FLUX
DENSITY (B)
• A magnetic field is a mathematical description of the
magnetic influence of electric currents and magnetic
materials.
• The magnetic field at any given point is specified by
both a direction and a magnitude (or strength). It is a
vector quantity.
• The magnetic field is most commonly defined in
terms of the Lorentz force it exerts on moving
electric charge.

17. • A particle of charge q (stationary)in an electric field E
experiences a force
• When a charged particle moves in the vicinity of a
current-carrying wire, the force also depends on the
velocity of that particle.
• How to measure the direction
and magnitude of
the vector B?
1. Take a particle of known charge q. Measure the force on
q at rest, to determine E.
2. Then measure the force on the particle when its
velocity is v.
3. Find a B that makes the Lorentz force law fit all these
results—that is the magnetic field at the place.
)( vBEqF 
qEF 

18. • B- Magnetic flux density (unit: teslas-T)
Magnetic flux:
The magnetic flux through a surface is
the component of the magnetic B field passing
through that surface.
;A-area
• θ is the angle between the surface and
magnetic flux lines direction.
• Unit of - weber (Wb) (SI units)
maxwell(Mx) (CGS)
1 weber=108 maxwell
or
)( Bor

2
/ meterweber
A
B


2
/11 mWbT 
2
/ cmMx
A
B


2
/1)(1 cmMxGgauss 
 sinBA

19. 0
cos BA

20. m.m.f
• Magneto motive force (m.m.f-θ or F) is the strength
of a magnetic field in a coil of wire.
• Dependent on how much current flows in the turns
of coil.
(i) the more current, the stronger the magnetic field.
(ii) the more turns of wire, the more concentrated the
lines of force.
turnsamperNIF  )(

21. Reluctance(S/R):
Magnetic reluctance, or magnetic resistance is
analogous to resistance in an electrical circuit.
 rather than dissipating electric energy it stores
magnetic energy.
 A magnetic field causes magnetic flux to follow the
path of least magnetic reluctance.
Reluctance=m.m.f/flux
Ampere-turns/weber (A-t/Wb)

F
S 
Unit: inverse henries (H-1)

22. Permeability(μ):
In electromagnetism, permeability is the measure of
the ability of a material to support the formation of a
magnetic field within itself.
Unit: henries /meter (H·m−1)
 The permeability constant (μ0)/ the magnetic
constant/permeability of free space, is a measure of
the amount of resistance encountered when forming
a magnetic field in a vacuum.
 Permeability of any material(μ) is given by
H.m-1
μr – relative permeability of the medium
or   meterhenries/104 7
0

 

23. Magnetic Field strength (H):
Magnetic field strength at any point within a magnetic
field is numerically equal to the force experienced by a
N-pole of one weber placed at that point.
• Unit – N/Wb, A-t/m
• Flux density B=μH Wb/m2
• Flux density developed in vacuum, B0= μ0H
• Relative permeability
Relative permeability of a material is equal to the
ratio of the flux density produced in that material to
the flux density produced in vacuum by the same
magnetising force.
00 B
B
r 




24. Magnetic circuit
A
l
A
l
SR
r 0

SHlNI 
Reluctance(R/S)=
m.m.f=

25. Series magnetic circuit

26. μi =relative permeability of iron

27. Series -parallel magnetic circuits

29. Magnetic circuit

30. Force on a current carrying conductor
placed in a magnetic field
1. A conductor carrying a current can produce a force on a
magnet situated in the vicinity of the conductor.
2. By Newton’s third law of motion, namely that to every force
there must be an equal and opposite force, it follows that the
magnet must exert an equal force on the conductor.

31. Fleming’s left hand rule
• The rule can be summarized as follows:
1. Hold the thumb, first finger and second finger of the left hand as shown
in figure , whereby they are mutually at right angles.
2. Point the First finger in the Field direction.
3. Point the seCond finger in the Current direction.
4. The thuMb then indicates the direction of the Mechanical force exerted
by the conductor.
Cause
Effect
This law is Used in motors

32. • Force (F) depends on
(1) Magnetic flux density
(2) Current through the conductor
F= force on the conductor (newtons)
B=magnetic flux density (teslas)
= length of the conductor (meters)
= current through the conductor (ampers)
θ= angle between and
If θ=90o then,
sinBlIF 
l
I
l B
BlIF 

33. Flemings left hand rule

34. Relation between magnetism and
electricity
• After the discovery that electricity produces a
magnetic field, scientist began to search for the
converse phenomenon from about 1821.
• How to convert magnetism into electricity?
• Michael Faraday succeeded in producing by
converting magnetism.
• In 1831, he formulated basic laws underlying the
phenomenon of electromagnetic induction
“Faraday’s Laws of electromagnetic induction”

35. Faraday’s experiment
Experiment 1
Experiment 2
Fig (a)
Fig (b)

36. • In 1831, Michael Faraday made the great discovery of
electromagnetic induction,
namely a method of obtaining an electric current with the aid of
magnetic flux.
• He wound two coils, A and C, on a steel ring R, as in Fig. (a)
and found that, when switch S was closed, a deflection was
obtained on galvanometer G, and that, when S was opened, G
was deflected in the reverse direction.
• A few weeks later he found that, when a permanent magnet
NS was moved relative to a coil C (Fig. b), galvanometer G was
deflected in one direction when the magnet was moved
towards the coil and in the reverse direction when the magnet
was withdrawn.

37. • It was this experiment that finally convinced
Faraday that an electric current could be
produced by the movement of magnetic flux
relative to a coil.
• Faraday also showed that the magnitude of the
induced e.m.f. is proportional to the rate at which
the magnetic flux passed through the coil is
varied.
• Alternatively, we can say that, when a conductor
cuts or is cut by magnetic flux, an e.m.f. is
generated in the conductor and the magnitude of
the generated e.m.f. is proportional to the rate at
which the conductor cuts or is cut by the
magnetic flux.

38. Statically and dynamically induced
E.M.F.
• Statically induced e.m.f:
Conductors or the coil remains
stationary and flux linked with it is changed.
• Dynamically induced e.m.f:
Field is stationary and conductors cut
across the field.

39. Faradays laws of electromagnetic
induction
• First law:
It states that, whenever the magnetic flux
linked with a circuit changes, an e.m.f is
always induced in it.
(or)
Whenever a conductor cuts magnetic flux, an
e.m.f is induced in that conductor

40. • Second law:
When the magnetic flux linking a conductor is
changing, an e.m.f is induced whose magnitude is
proportional to the rate of change of flux- linkages.
N- number of turns in the coil C
 The flux through the coil
Changes from an initial value of
Φ1 webers to the final value of
Φ2 webers in time ‘t’ seconds.
Initial flux linkages= NΦ1
Final flux linkages= NΦ2
induced e.m.f(e) is, (statically induced e.m.f)
sWb
t
NN
e /12





 



41. volt
t
NN
e 




 
 12 
t
N
e
)( 12  

Putting the above expression in its differential form,
volt
dt
d
NN
dt
d
e

  )(

42. Dynamically induced e.m.f
• Induced e.m.f (e),
sinBlve 

43. • What is the direction of the induced e.m.f or current
produced by induced e.m.f ?
• We have 2 methods to find this.
1. Fleming right hand rule
2. Lenz’s Law

44. Fleming’s right hand rule
• Field or Flux - First finger
• Motion of the conductor relative to the flux- ThuMb finger
• Induced E.m.f. - SEcond finger.
cause
effect
This principle is used in generators

45. Lenz’s Law
• In 1834 Heinrich Lenz, a German physicist,
intoduced this law.
• The direction of an induced e.m.f. is always
such that it tends to set up a current opposing
the motion or the change of flux responsible
for inducing that e.m.f.

46. Inductance
• Inductance is the property of an electric circuit
which opposes any sudden change in current.
• Although a straight conductor possesses
inductance, the property is most marked in a
coil

48. Self inductance(L)
l
AN
L
2


I
N
L

Method 1
Method 2
Method 3
dt
dI
LeL 

49. Self and mutual inductance
• In electromagnetism and electronics,
inductance is the property of a conductor by
which a change in current in the conductor
"induces" (creates) a voltage (electromotive
force) in both the conductor itself (self-
inductance) and in any nearby conductors
(mutual inductance)

50. 1
12
I
N
M

Method 1
Method 2
S
NN
M 21

Method 3
dt
dI
MeM
1


51. Coefficient of couplings
21LL
M
k 
Ranges from(0-1)

52. Energy stored in magnetic field
2
2
1
LIE 

53. Charging and discharging of inductor
and time constant
)1( 
t
m eIi


discharging
charging

t
meIi



54. • A text book of electrical technology (volume 1)
by B.L.THERAJA. (S. chand publications)
• Electrical technology (Electrical fundamentals)
volume 1 by SURINDER PAL BALI (Pearson)
• Elements of electrical engineering by U.A
PATEL (ATUL)