Presentation on Electro Magnetism

1. Prepared by:
Ikram Arshad (1897-2017)
Bilal Raza (2383-2017)
Abdullah Khero (2862-2016)
Hamza Kaiser (3126-2017)
Presented To:
Dr Engr. Taj Muhammad Baloch

2. Magnetism
• Is the study of magnetic fields and their
effect on materials.
• The effect is due to unbalanced spin of
electrons in atom.
• It is readily observed every day – from
the simple magnet that attracts nails
and other metals to cassette tapes to
magnet-driven trains.

3. Magnetism
• In terms of applications, magnetism is one of the
most important fields in physics.
• Large electromagnets are used to pick up heavy
loads.
• Magnets are used in such devices as meters,
motors, and loudspeakers.
• Magnetic tapes and disks are used routinely in
sound-and video-recording equipment and to
store computer data.
• Intense magnetic fields are used in magnetic
resonance imaging (MRI) devices to explore the
human body with better resolution and greater
safety than x-rays can provide.

4. Magnetism
• Giant superconducting magnet are used in the
cyclotrons that guide particles into targets at nearly
the speed of light.
• Magnetism is closely linked with electricity.
• Magnetic fields affect moving charges, and moving
charges produce magnetic fields.
• Changing magnetic field can even create electric
fields.
• These phenomena signify an underlying unity of
electricity and magnetism, which James Clerk
Maxwell first described in the 19th century.
• The ultimate source of any magnetic field is electric
current.

5. Nature of Magnetism
• In the ancient country of Lydia, in
western Asia Minor, now Turkey, was
a city called Magnesia.
• The Greeks discovered that certain
iron ores found in the place could
attract other pieces or iron, they called
it magnetites.
• Magnetites are classified as natural
magnet.

6. Nature of Magnetism
It is now believed that
magnetism is due to the
spin of electrons within
the atoms.
Since the electron is a
charged
concept
particle, the
implies that
magnetism is a property
of a charged particle in
motion.

7. Nature of Magnetism
• The power of attraction of a magnet
depends on the arrangement of the
atoms.
• All atoms are in themselves tiny
magnet formed into groups called
DOMAINS.
• The magnetic strength is increased if
the domains are induced to fall into
line by the action of another magnet.

8. General Properties of Magnet
• The properties of naturally occurring
magnets (magnetites) have been
known for over 2,000 years.
• Several studies on magnetism were
made, but the first
investigation was done by
thorough
William
Gilbert in 1600.
• Experimental results led to the
discovery of the many properties of
natural and artificial magnets.

9. General Properties of Magnet
1. Magnets usually have two poles.
• The end of the magnet which points north when
magnet is free to turn on a vertical axis is the
north-seeking pole, simply the N pole.

10. General Properties of Magnet
• The opposite end which points south is the
south-seeking pole or S pole.
• Magnets come in many shapes and sizes, but
each has at least two poles.
• If you cut a magnet into pieces, every piece will
still have at least two poles.

11. General Properties of Magnet
2. Like Magnetic poles repel and
unlike poles attract.

12. General Properties of Magnet
Charles Augustine de Coulomb,
a French physicist, was the first
scientist to study
the force exerted
recognized
quantitatively
by magnets.
The result of his experiments are
summarized in what is known as
Coulomb’s Law of Magnetism:
“The force of attraction/repulsion
between two magnetic poles is directly
proportional to the strength of the
poles and inversely proportional to the
square of the distance between them”.

13. The result
summarized in what is known
of his experiments are
as
Coulomb’s Law of Magnetism:
“The force of attraction/repulsion
between two magnetic poles is directly
proportional to the strength of the
poles and inversely proportional to the
square of the distance between them”.

14. General Properties of Magnet
3. A piece of
magnetite, when
made to hang and
swing freely,
would align itself
with the magnetic
field of the earth
following a north-
south direction.

15. General Properties of Magnet
magnets made from alloys
4. Permanent magnets are
of
cobalt and nickel.
These magnets retain
their magnetism for a
long time.

16. General Properties of Magnet
5. Other metals like iron can be
magnetized by Induction.
When a piece of iron nails
touches a permanent magnet,
the nails becomes a magnet.
It retains in this condition for as
long as it is within the magnetic
field.
The nail is a temporary magnet
and its magnetism is described
as induced magnetism.

17. Magnetic Field of Force
• Experiment show that a stationary charged
particle doesn’t interact with a static magnetic
field.
• When a charged particle is moving through a
magnetic field, however, a magnetic force
acts on it.
• The force has its maximum value when the
charge moves in a direction perpendicular to the
magnetic field line, decreases in value at other
angles, and becomes zero when moves along
the field of lines.

18. Magnetic Field of Force
• Magnetic force on a moving charge is directed
perpendicular to the magnetic field.
• It is found experimentally that the strength of the
magnetic force on the particle is proportional to
the magnitude of the charge q, the magnitude of
the velocity v, the strength of the external
magnetic field B, and the sine of the angle
between the direction of v and the direction of B.
F = qvB sin θ
• This expression is used to define the magnitude
of the magnetic field as:
F
B =
qv sin θ

19. Earth’s Magnetic Field
• A small bar magnet is said to have north
and south poles, but is it more accurate
to say it has a “north-seeking” pole and
“south-seeking” pole.
• By this expressions, we mean that if
such a magnet is used as a compass,
one end will “seek” or point to, the
geographic North Pole of Earth and the
other end will “seek” or point to, the
geographic South Pole of Earth.

20. • We therefore conclude that:
The Geographic North Pole of Earth corresponds
to a magnetic south pole, and the geographic
South Pole of Earth corresponds to a magnetic
north pole.
Earth’s Magnetic Field

21. • The magnetic field pattern of Earth is
similar to the pattern that would be set
up by a bar magnet placed at its center.
• An interesting fact concerning Earth’s
magnetic field is that its direction
reverses every few million years.
Earth’s Magnetic Field

22. Earth’s Magnetic Field and its Present
Application – Labeling Airport Runways
• The magnetic field of Earth is used to label
runways at airports according to their direction.
• A large number is painted on the end of the
runway so that it can be read by the pilot of an
incoming airplane.

23. magnetic heading, in degrees measured
clockwise from magnetic north divided by 10.
• A runway marked 9 would be directed toward
the east (900 divided by 10), whereas a runway
marked 18 would be directed toward magnetic
south.
Earth’s Magnetic
Field and its
Present Application
– Labeling Airport
Runways
• This number describes the direction in which
the airplane is traveling, expressed as the

24. Right-Hand Rule #1
The implications of this expression include:
1. The force is perpendicular to both the velocity v of
the charge q and the magnetic field B.
2.The magnitude of the force is F = qvB sinθ where θ
is the angle < 180 degrees between the velocity and
the magnetic field. This implies that the magnetic
force on a stationary charge or a charge moving
parallel to the magnetic field is zero.
3.The direction of the force is given by the right hand
rule.

25. Right-Hand Rule # 1
Right-Hand Rule #1 determines the directions
of magnetic force, conventional current and the
magnetic field. Given any two of these, the
third can be found.
Using your right-hand:
1.point your index finger in the
direction of the charge's
velocity, v, (recall conventional
current).
2.Point your middle finger in the
direction of the magnetic field,
B.
3.Your thumb now points in
the direction of the magnetic
force, Fmagnetic.

26. Right-Hand Rule # 1
When the magnetic force relationship is applied
to a current-carrying wire, the right-hand rule
may be used to determine the direction of force
on the wire.

27. Right-Hand Rule # 2
Right-Hand Rule #2 determines the direction
of the magnetic field around a current-
carrying wire and vice-versa
Using your right-hand:
Curl your fingers into
a half-circle around
the wire, they point in
the direction of the
magnetic field, B
Point your thumb in
the direction of the
conventional current.

28. Magnetic Force on a Current-
Carrying Conductor
• If a straight conductor of length ℓ carries current,
the magnetic force on that conductor when it is
placed in a uniform external magnetic field B is:
F = BIℓ sin θ
• Where
 Ɵ is the angle between the direction of the current
and the direction of the magnetic field.
 B is the direction of the current.
 I is the current
 ℓ is the length of the wire

29. Magnetic Force on a Current-
Carrying Conductor
• Right-hand rule #1 also gives the direction of
the magnetic force on the conductor. In this
case, however, you must point your fingers in
the direction of the current rather than in the
direction of v.

30. Application:
• A magnetic force acting on a current-carrying
wire in a magnetic field is the operating
principle of most speakers in sound systems.

31. Application:
• Speaker is consists of a coil of wire called the voice
coil, a flexible paper cone that acts as the speaker,
and a permanent magnet.
• The coil of wire is surrounding the north pole of the
magnet is shaped so that the magnetic field lines are
directed radially outward from the coil’s axis.
• When an electrical signal is sent to the coil,
producing a current in the coil, a magnetic force to
the left acts on the coil. (can be seen by applying
right-hand rule #1 to each turn of wire).

32. Application:
• When the current reverses direction, as it would
for a current that varied sinusoidally, the
magnetic force on the coil also reverses
direction, and the cone, which is attached to the
coil, accelerates to the right.
• An alternating current through the coil causes
an alternating force on the coil, which results in
vibrations of the cone.
• The vibrating cone creates sound waves as it
pushes and pulls on the air in front of it.
• In this way, a 1-kHz electrical signal is
converted to a 1-kHz sound waves.

33. Torque on a Current Loop and
Electric Motor
• The torque Ƭ on a current-carrying loop of wire in a
magnetic field B has magnitude:
Ƭ = BIA sin θ
• Where:
 I is the current in the loop
 A is the cross-sectional area
• The magnitude of the magnetic moment of the
current-carrying coil is defined by µ = IAN
 N is the number of loops
• The magnetic moment is considered vector, µ, that
is perpendicular to the plane of the loop.
• The angle between B and µ is θ.

34. Application:
• Its hard to imagine life in the 21st century withoutmotors.
• Some of
computer
the appliances that contain motors include
disk drives, CD players, DVD players, food
processors and blenders, car starters, furnaces, and air
conditioners.
• The motors convert electrical energy to kinetic energy of
rotation and consist of a rigid current-carrying loop that
rotates when placed in the field of a magnet.

35. Magnetic Field of a Long,
Straight Wire
During the
demonstration
1819, Danish
lecture
in
Scientist
Hans Oersted found than
an electric current in a wire
deflected a nearby
compass needle.
This momentous discovery, linking a magnetic
field with an electric current for the first time,
was the beginning of our understanding of the
origin of magnet.

36. Magnetic Field of a Long,
Straight Wire
• In the simple experiment carried by Oersted in
1820, several compass needles are placed in a
horizontal plane near a long vertical wire.

37. • When there is no current in the wire, all needles
point in the same direction (that of Earth’s field),
as one would expect.
Magnetic Field of a Long,
Straight Wire
• When the wire carries a
strong, steady current,
however, the needles all
deflect in directions
tangent to the circle.

38. • The observation of Oersted show that the
direction of B is consistent with the following
convenient rule, Right-Hand Rule # 2.
Magnetic Field of a Long,
Straight Wire