# Unit 11 Magnetism.

## Presentation on theme: "Unit 11 Magnetism."— Presentation transcript:

Unit 11 Magnetism

Magnets magnetism – force of attraction or repulsion
not all objects are affected by the force of magnetism ex. wood, glass, paper, plastic common metals affected by magnetism are iron, nickel, and cobalt

Magnets poles – two ends of a magnet every magnet has two poles
north (N) pole south (S) pole even if you break a magnet in half, each half will have a north pole and a south pole

Magnets the north pole of a magnet points North
it is often called “North-seeking”

Properties of Magnets if a north pole and a south pole are brought together, they will attract each other opposites attract

Properties of Magnets if the north pole of one magnet is brought near the north pole of another magnet, they will repel each other if two south poles are brought together, they will repel each other

Properties of Magnets like magnetic poles repel each other
unlike magnetic poles attract each other

Magnetic Fields magnetic field – area around a magnet where magnetic forces can act a magnetic field is made up of magnetic lines of force

Magnetic Fields magnetic lines of force – lines that show the shape of a magnetic field the magnetic lines of force are closest together at the poles of the magnet this is where the magnet is strongest

Making a Magnet some magnets occur in nature
these magnets are called natural magnets ex. magnetite (also called lodestone)

Making a Magnet materials that are not natural magnets can be magnetized

Making a Magnet magnetic induction – process by which a material can be made into a magnet

Making a Magnet some materials are easy to magnetize ex. iron

Making a Magnet a material that is easily magnetized tends to lose its magnetism quickly a magnet made of this kind of material is called a temporary magnet

Making a Magnet materials that are hard to magnetize will also stay magnetized for a long time a magnet that is hard to magnetize but tends to keep its magnetism is called a permanent magnet

The Earth as a Magnet William Gilbert a British scientist
the Earth has north and south poles like a bar magnet

The Earth as a Magnet the Earth has a North Magnetic Pole and a South Magnetic Pole the North Magnetic Pole is located near the geographic North Pole the South Magnetic Pole is located near the geographic South Pole

The Earth as a Magnet the North Magnetic Pole is like the south pole of a bar magnet the South Magnetic Pole is like the north pole of a bar magnet

The Earth as a Magnet the Earth is surrounded by a magnetic field which extends far into space magnetosphere – region of the Earth’s magnetic field

The Earth as a Magnet the magnetosphere traps charged particles from the sun when these particles enter the atmosphere, an aurora is formed auroras are also called the northern and southern lights

Electricity and Magnetism
Hans Oersted about 200 years ago an electric current flowing in a wire causes a compass needle to move

Electricity and Magnetism
an electric current passing through a wire causes a magnetic field

Electricity and Magnetism
electromagnetism – relationship between electricity and magnetism

Electricity and Magnetism
Michael Faraday (British scientist) Joseph Henry (American scientist) when a wire is moved across a magnetic field, an electric current is induced in the wire

Electricity and Magnetism
electromagnetic induction – process by which an electric current is produced by moving a wire in a magnetic field

Electricity and Magnetism
a wire carrying an electric current always has a magnetic field around it the magnetic field in a straight wire is not very strong if the wire is wound into a coil, the magnetic field becomes much stronger as the individual magnetic fields overlap the greater the number of coils, the stronger the magnetic field

Electromagnets electromagnet – temporary magnet made by wrapping a current-carrying wire around an iron core the center of an electromagnet is called the core it is often made of iron

Electromagnets as long as current is flowing, an electromagnet has a magnetic field when current is turned off, there is no longer a magnetic field

Electromagnets there are two ways to make an electromagnet stronger
increasing the number of coils increasing the amount of current

Electromagnets electromagnets are useful because they can be turned on and off electromagnets have many important uses ex. radios, telephones, computers

Electromagnets changing the direction of an electric current causes the poles of an electromagnet to reverse this feature is important in the production of electric motors

Transformers transformer – device in which alternating current in one coil of wire induces a current in a second coil

Transformers a transformer consists of two coils of wire around a magnet the first coil, called the primary coil, is connected to the power source the second coil, called the secondary coil, is connected to the load a load is something that uses electricity, such as a light bulb or a motor

Transformers a transformer only works with alternating current

Transformers a step-up transformer increases voltage
it consists of more coils of wire in the secondary coil than the primary coil

Transformers a step-down transformer decreases voltage
it consists of more coils of wire in the primary coil than the secondary coil

Electric Motors electric motor – device that changes electrical energy into mechanical energy

Electric Motors an electric motor is made up of an electromagnet and a permanent magnet

Electric Motors the electromagnet is free to turn and is hooked up to a source of alternating current changing the direction of an electric current causes the poles of an electromagnet to reverse

Electric Motors attraction and repulsion between the electromagnet and the permanent magnet cause the electromagnet to spin

Electric Motors an electric motor can use direct current if a special switch is used

Generators generator – device that changes mechanical energy into electrical energy a current can be induced in a loop of wire by spinning the loop inside a magnetic field due to the changing direction of the wire, an alternating current is produced

Generators an electric generator is made up of an insulated loop of wire and a U-shaped magnet spinning the loop of wire in the magnetic field of the magnet produces an electric current

Generators most of the energy we use every day comes from generators

Generators mechanical energy for many generators is supplied by turbines a turbine is a large wheel that is turned by moving steam or water