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Chapter 2 Chapter 2 Magnetism and Magnetism and Electromagnetism Electromagnetism By : Dayang khadijah By : Dayang khadijah ppkkp ppkkp

Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

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Page 1: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

Chapter 2Chapter 2Magnetism and Magnetism and

ElectromagnetismElectromagnetismBy : Dayang khadijahBy : Dayang khadijah

ppkkpppkkp

Page 2: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

THE MYSTERY OF THE MYSTERY OF

MAGNETISMMAGNETISM •Each time you turn on a light, listen to your stereo, fly in an airplane, or watch TV, you are depending on the principles of magnetism to work for you.

•Take a look at the pictures below. All of the items in these pictures have something to do with magnetism.

Hydroelectric Dam Video Cassette Tape

Page 3: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

FanMagnetic Particle Inspection Unit

Airplane Navigational Panel

Page 4: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

What is magnetism?What is magnetism?

Just like when the Greeks of the old times discovered Just like when the Greeks of the old times discovered the first naturally occurring magnetic stones, or natural the first naturally occurring magnetic stones, or natural magnets, you have been observing a property of matter magnets, you have been observing a property of matter called called magnetismmagnetism. .

Magnetism is the force of attraction or repulsion in and Magnetism is the force of attraction or repulsion in and around a material. Magnetism is present is all around a material. Magnetism is present is all materials but at such low levels that it is not easily materials but at such low levels that it is not easily detected.  Certain materials such as magnetite, iron, detected.  Certain materials such as magnetite, iron, steel, nickel, cobalt and alloys of rare earth elements, steel, nickel, cobalt and alloys of rare earth elements, exhibit magnetism at levels that are easily detectable.exhibit magnetism at levels that are easily detectable.

Page 5: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• Magnetism is a basic force of attraction and repulsion in nature that is created, by moving charges.

• A magnet is an object, which has a magnetic field that causes a push or pulling action.

• Similar to electric charges, unlike poles attract, while like poles repel

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Page 6: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• Magnetism is a basic force of attraction and repulsion in nature that is created, by moving charges.

• A magnet is an object, which has a magnetic field that causes a push or pulling action.

• Similar to electric charges, unlike poles attract, while like poles repel

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Page 7: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

What is a magnet?What is a magnet? A magnet is any piece of material that has A magnet is any piece of material that has

the property of attracting iron (or steel). the property of attracting iron (or steel). Magnetite, also known as lodestone, is a Magnetite, also known as lodestone, is a naturally occurring rock that is a magnet. naturally occurring rock that is a magnet.

This natural magnet was first discovered in a This natural magnet was first discovered in a region known as magnesia and was named region known as magnesia and was named after the area in which it was discovered. after the area in which it was discovered.

Magnetism may be naturally present in a Magnetism may be naturally present in a material or the material may be artificially material or the material may be artificially magnetized by various methods. Magnets magnetized by various methods. Magnets may be permanent or temporary.may be permanent or temporary.

Page 8: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

After being magnetized, a permanent magnet will retain the After being magnetized, a permanent magnet will retain the properties of magnetism indefinitely. properties of magnetism indefinitely.

A temporary magnet is a magnet made of soft iron, that is A temporary magnet is a magnet made of soft iron, that is usually easy to magnetize; however, temporary magnets lose usually easy to magnetize; however, temporary magnets lose most of their magnetic properties when the magnetizing cause most of their magnetic properties when the magnetizing cause is discontinued. is discontinued.

Permanent magnets are usually more difficult to magnetize, Permanent magnets are usually more difficult to magnetize, but they remain magnetized. Materials which can be but they remain magnetized. Materials which can be magnetized are calledmagnetized are calledferromagnetic materialsferromagnetic materials

Page 9: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

What is happening when you cut a magnet?What is happening when you cut a magnet?

A magnet can be cut into smaller and smaller pieces A magnet can be cut into smaller and smaller pieces indefinitely, and each piece will still act as a small indefinitely, and each piece will still act as a small magnet. magnet.

Thus, the cause of magnetism must be from a Thus, the cause of magnetism must be from a property of the smallest particles of the material, the property of the smallest particles of the material, the atoms. atoms.

Page 10: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• magnets do not come in separate charges • Any magnetic/magnetized object has a North

and South pole

• If you break a magnet in half, each piece will have a North and a South end

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Page 11: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

A magnetic field describes a volume of space where there is a

change in energy. As Ampere suggested, a magnetic field is

produced whenever an electrical charge is in motion.

The spinning and orbiting of the nucleus of an atom produces a

magnetic field as does electrical current flowing through a wire.

The direction of the spin and orbit determine the direction of the

magnetic field. The strength of this field is called the magnetic

moment.

•What is a magnetic field and how is it created?

Page 12: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

The motion of an electric charge producing a The motion of an electric charge producing a

magnetic field is an essential concept in magnetic field is an essential concept in

understanding magnetism. understanding magnetism.

The magnetic moment of an atom can be the result of The magnetic moment of an atom can be the result of

the electron's spin, which is the electron orbital the electron's spin, which is the electron orbital

motion and a change in the orbital motion of the motion and a change in the orbital motion of the

electrons caused by an applied magnetic field.electrons caused by an applied magnetic field.

Page 13: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• Magnetic field lines – 3D lines which tiny bar magnets lie along. Magnetic field lines run from N to S.

• A compass can be used to map out the magnetic field.

• Field forms closed “flux lines” around the magnet (lines of magnetic flux never intersect)

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Page 14: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

MAGNETIC LINES OF FORCEMAGNETIC LINES OF FORCE What do the lines around the bar magnet indicate?What do the lines around the bar magnet indicate?

The lines that we have mapped out around the The lines that we have mapped out around the magnet, called the magnet, called the magnetic lines of forcemagnetic lines of force, indicate , indicate the region in which the force of the magnet can be the region in which the force of the magnet can be detected. detected.

This region is called the This region is called the magnetic fieldmagnetic field. If an iron . If an iron object is near a magnet, but is not within the magnetic object is near a magnet, but is not within the magnetic field, the object will not be attracted to the magnet. field, the object will not be attracted to the magnet.

Page 15: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

When the object enters the magnetic field, the force When the object enters the magnetic field, the force of the magnet acts, and the object is attracted.of the magnet acts, and the object is attracted.

The pattern of these lines of force tells us something The pattern of these lines of force tells us something about the characteristics of the forces caused by the about the characteristics of the forces caused by the magnet. magnet.

The magnetic lines of force, or flux, leave the north The magnetic lines of force, or flux, leave the north pole and enter the south pole.pole and enter the south pole.

Page 16: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

Magnetic fieldMagnetic field

• The strength of the magnetic field is greater where the lines are closer together and weaker where they are farther apart.

• Field is strongest in regions of dense field lines.

• Field is weakest in regions of sparse field lines.

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Page 17: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

The density of field lines indicates the strength of

the field

Strong Field

Weak Field

Magnetic field

Page 18: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

Magnetic fluxMagnetic flux

• Magnetic flux is measurement of the quantity of magnetism, the description of how certain materials relate to magnetic fields.

• Specifically, it describes the strength and extent of the object's interaction with the field.

• Magnetic lines of force (flux) are assumed to be continuous loops.

• Magnetic flux measured in Webers (Wb) • Symbol

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Page 19: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

Since the earth is a huge magnet with a magnetic Since the earth is a huge magnet with a magnetic north and south pole, the lines of magnetic force north and south pole, the lines of magnetic force around the earth look like there is a huge vertical bar around the earth look like there is a huge vertical bar magnet running through the center of the earth. magnet running through the center of the earth.

How is the earth like a magnet?

Page 20: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

The Earth is a MagnetThe Earth is a Magnet• A magnetic compass aligns itself along the

magnetic field lines (produced by the Earth in the absence of a stronger field)

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Page 21: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• The North pole of the compass points to the Earth magnetic South pole (generally toward geographic north) and vice‐versa

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Page 22: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

FERROMAGNETIC FERROMAGNETIC MATERIALSMATERIALS

Notice that even though the paper clip Notice that even though the paper clip alone are not magnetic, when they are alone are not magnetic, when they are attached to a magnet, they become a little attached to a magnet, they become a little magnets themselves.magnets themselves.

Page 23: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

We have determined in previous discussions that We have determined in previous discussions that magnets can be permanent or temporary. A magnets can be permanent or temporary. A permanent magnet is more difficult to magnetize but permanent magnet is more difficult to magnetize but will retain the properties of magnetism indefinitely.will retain the properties of magnetism indefinitely.

A temporary magnet is generally made of soft iron A temporary magnet is generally made of soft iron and will remain magnetized only as long as the and will remain magnetized only as long as the magnetizing cause is present. magnetizing cause is present.

How does an object become a magnet?

Page 24: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

Bringing a ferromagnetic object, like a nail, into the Bringing a ferromagnetic object, like a nail, into the magnetic field of a strong magnet can cause the magnetic field of a strong magnet can cause the molecules of the iron material to line up and the nail molecules of the iron material to line up and the nail to become a temporary magnet. to become a temporary magnet.

As long as it is in the magnetic field of the bar As long as it is in the magnetic field of the bar magnet, the nail acts like a magnet and picks up other magnet, the nail acts like a magnet and picks up other ferromagnetic materials.ferromagnetic materials.

In this case it is the paper clip. Then, the paper clip In this case it is the paper clip. Then, the paper clip becomes a magnet and can pick up another paper clip, becomes a magnet and can pick up another paper clip, and so forth.and so forth.

Page 25: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• Magnetism can be transferred or induced into other materials, this is known as Magnetic Induction

• The induction of magnetism into a material can be permanent or temporary

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Page 26: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• Magnetic materials (ferromagmagnetic): iron, steel, cobalt, nickel and some of their alloys.

• Non magnetic materials: water, wood, air, quartz.

• In an un-magnetised state, the molecular magnets lie in random manner, hence there is no resultant external magnetism exhibited by the iron bar.

wood

Non-magnetic molecules

Iron bar

Magnetic molecules

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Page 27: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• When the iron bar is placed in a magnetic field or under the influence of a magnetising force, then these molecular magnets start turning their axes and orientate themselves more or less along a straight lines.

Iron bar

Magnetic molecules

S N

SN

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Page 28: Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

• When the iron bar is placed in a very strong magnetic field, all these molecular magnets orientate themselves along a straight lines (saturated).

Iron barMagnetic molecules

S N

N S

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