Chapter 2 Magnetism and Electromagnetism By : Dayang khadijah ppkkp

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

  • Chapter 2Magnetism and Electromagnetism

    By : Dayang khadijahppkkp

  • THE MYSTERY OF MAGNETISM 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

  • FanMagnetic Particle Inspection Unit Airplane Navigational Panel

  • What is magnetism? Just like when the Greeks of the old times discovered the first naturally occurring magnetic stones, or natural magnets, you have been observing a property of matter calledmagnetism.

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

  • 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


  • 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


  • What is a magnet? A magnet is any piece of material that has the property of attracting iron (or steel). Magnetite, also known as lodestone, is a naturally occurring rock that is a magnet.

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

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

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

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

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

  • What is happening when you cut a magnet?

    A magnet can be cut into smaller and smaller pieces indefinitely, and each piece will still act as a small magnet. Thus, the cause of magnetism must be from a property of the smallest particles of the material, the atoms.

  • 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*

  • Amagnetic fielddescribes 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 themagnetic moment.

    What is a magnetic field and how is it created?

  • The motion of an electric charge producing a magnetic field is an essential concept in understanding magnetism. The magnetic moment of an atom can be the result of the electron's spin, which is the electron orbital motion and a change in the orbital motion of the electrons caused by an applied magnetic field.

  • 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)


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

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

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

  • When the object enters the magnetic field, the force of the magnet acts, and the object is attracted. The pattern of these lines of force tells us something about the characteristics of the forces caused by the magnet. The magnetic lines of force, or flux, leave the north pole and enter the south pole.

  • Magnetic fieldThe 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.


  • The density of field lines indicates the strength of the fieldStrong FieldWeak FieldMagnetic field

  • Magnetic fluxMagnetic 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


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

  • The Earth is a MagnetA magnetic compass aligns itself along the magnetic field lines (produced by the Earth in the absence of a stronger field)


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


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

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

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

    How does an object become a magnet?

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

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

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

  • Magnetism can be transferred or induced into other materials, this is known as Magnetic InductionThe induction of magnetism into a material can be permanent or temporary


  • 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.*

  • 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. *

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