Unit 35

Magnetic Forces and Fields

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.

What is a magnet?

Magnetic field =surrounds a magnet and can exert magnetic forces.

Magnetic force =the force a magnet exerts on another magnet, on iron, or a similar metal, or on moving charges (magnetic force is one aspect of electromagnetic force)

Magnetic Forces and Fields

Magnetic field =surrounds a magnet and can exert magnetic forces.

Fig. 35.1.1. Magnetic field lines – single magnet Fig. 35.1.2. Magnetic field lines – two magnets

Iron filings lining up along the magnetic field

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

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.

Magnetic Poles

The magnetic field is a dipole field. That means that every magnet MUST have two poles, a positive (+) or negative (−) electrical charge (a north and a south pole).

Electrical charges are called monopoles, since they CAN exist without the opposite charge.

Hans Christian Oersted He discovered the connection

between electricity and magnets by chance in 1820.

As he prepared for one of his classes, he noticed that when he turned on the electric current in a wire, a compass needle that was on another experiment changed its position.

When the electric current was turned off, the compass needle returned to its original position.

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

Turbines Closed-cycle pressurized water turbines

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