Electromagnetism

Behavior of Charges

Magnetism

•Magnetism is a class of physical phenomena that includes forces exerted by magnets on other magnets.

•The earliest magnets were found naturally in the mineral magnetite which is abundant the rock-type lodestone. These magnets were used by the ancient peoples as compasses to guide sailing vessels.

•Magnets produce magnetic forces and have magnetic field lines

What is a magnet?It is a substance that contains a magnetic field.There are three primary types of magnets:

Ferromagnetic- A substance that is naturally and permanently magnetic like iron.Paramagnetic- which becomes magnetic under the influence of a magnetic field.Electromagnet- Becomes magnetic under the influence of an electric current. Is no longer magnetic when electricity flow is stopped.

Magnets

Ferromagnets Paramagnet Electromagnet

Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together.Magnetic field =surrounds a magnet and can exert magnetic forces.

Unlike poles of magnets attract each other and like poles of magnets repel.

• A permanent magnet is a substance that holds a magnetic field indefinitely.

• Iron, Cobalt, and Nickel are the only substances that are naturally magnetic.

• But, Co and Ni are somewhat rare, so the vast majority of magnets are made of iron.

Permanent Magnet

Euro pennies have steel

The earth is like a giant magnet!The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

What are magnetic domains?Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field. These domains are typically composed of billions of atoms.

Electricity and Magnetism – how are they related?When an electric current passes through a wire a magnetic field is formed.

What is an electromagnet?When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

• An electromagnet starts with a power source and a wire.

• Batteries/Electricity produce electrons. • Flowing electrons produce an electric field, which

induces a magnetic field.• Electromagnetic devices are used to change electrical

energy into mechanical energy.• Examples of electromagnetic devices: electric motors,

galvanometers, loud speakers.

Electromagnetic devices:

• Electromagnets can easily be made at home with a copper wire, a nail, and a battery.

• Wrap the wire around the nail and hook it to the positive and negative ends of the battery.

• Suddenly the nail is magnetic and can attract iron objects.

Electromagnets

SOLENOID• A magnetic field in a current

carrying wire can be increased by wrapping the wire into a coil. This coil of wire is called a solenoid

• When a magnetic core is placed in a solenoid, an electromagnet is formed

• This is the basis of many electric motors.

What is a galvanometer?A galvanometer is an electromagnet that interacts with a permanent magnet. The stronger the electric current passing through the electromagnet, the more is interacts with the permanent magnet.

The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet.

Galvanometers are used as gauges in cars and many other applications.

What are electric motors?An electric motor is a device which changes electrical energy into mechanical energy.

Go to the next slide

How does an electric motor work?

We have seen how electricity can produce a magnetic field, but a magnetic field can also produce electricity! How?

What is electromagnetic induction?

Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction.

A generator is used to convert mechanical energy into electrical energy by electromagnetic induction.

Direct current versus alternating current – AC vs DC : What’s the difference?

Direct current is electrical current which comes from a battery which supplies a constant flow of electricity in one direction.

Alternating current is electrical current which comes from a generator. As the electromagnet is rotated in the permanent magnet the direction of the current alternates once for every revolution.

Right Hand Rule

• This magnetic field forms circles around a straight wire carrying the current.

• Point your thumb in the direction of the current (which is toward the negative terminal)

• If you curl your fingers around the wire, the way your fingers curve is in the direction of the magnetic field.

Electric Generator (Dynamo)• The opposite of an electromagnet is also true also!

• When a magnetic field rotates around a wire, it generates an electric current.

A hand-cranked dynamo charges a battery for an emergency radio…Or you can have a hamster do it

Turbines• Use water or wind to turn magnets to

generate electricity

To summarize• An electric current flowing

around a rod will make a magnet.

• It is called an electromagnet

• A moving magnetic field flowing around a wire will make electricity.

• It is called a generator

• Electricity and magnetism are both aspects of A. the north pole.

• B. the south pole. • C. electromagnetic force. • D. ferromagnetic material.

Quick Quiz

• Electricity and magnetism are both aspects of A. the north pole.

• B. the south pole. • C. electromagnetic force. • D. ferromagnetic material.

• When electric charges are moving through a wire, a magnetic field is created. The wires are made out of materials/metals that can be magnetized.

Quick Quiz

• A fan uses a rotating electromagnet to turn its blades. This is an example of

• A. magnetic poles. • B. an electric motor. • C. a galvanometer. • D. a loudspeaker.

Quick Quiz

• A fan uses a rotating electromagnet to turn its blades. This is an example of

• A. magnetic poles. • B. an electric motor. • C. a galvanometer. • D. a loudspeaker.

Quick Quiz

• A material such as iron that can be magnetized because it contains magnetic domains.

Ferromagnetic material

• A substance that reacts to magnetic fields, but does not remain so after the field is removed.

• Liquid Oxygen can remain suspended between two magnets.

Paramagnetic material

• The Earth acts as a giant electromagnet.

• There is a swirling liquid iron-nickel outer core floating around a solid iron-nickel inner core.

• Electrons moving around in the liquid create an electric current.

Earth as a magnet

• The moving current around the iron core makes for a giant magnetic field.

• This acts much like a magnet flowing around a wire, creating a strong magnetic field

Earth as a magnet

• The Earth’s magnetic field protects us from harmful solar particles by deflecting or absorbing them.

• The aurora borealis is located at the north pole, because that is where the energized solar particles come shooting down into the atmosphere.

Earth’s Magnetic Field

Aurora Borealis