Magnetism

Magnetism

• A magnet is an object that can attract other objects

containing iron, cobalt, or nickel.

• Magnetic substances are created when electrons from

within the atom or from another atom spins in the same

direction – this increases the magnetic field given off by

the electron (each spinning electron creates its own tiny

magnetic field)

• The spinning of electrons in the same direction causes a

north and south pole to form.

• Every magnet has at least one north pole and one south

pole.

• If you take a bar magnet and break it into two pieces,

each piece will again have a North pole and a South

pole.

S N S N S N

Materials can be classified 3 ways

• Non Magnet:

– Will not attract a magnet or a ferromagnetic substance

– Glass, plastic, rubber or wood

– Work well as insulators for electrical wires

• Ferromagnet

– Not a magnet but something that can become magnetized by

hitting, heating, or touching it with a magnet OR by adding an

electrical charge (electromagnet)

– Is attracted by a magnet

– Must contain one of the following: iron, nickel or cobalt

– The magnetism can be turned on and off.

• Permanent Magnet

– can attract another magnet AND a ferromagnetic substance

Ferromagnet Magnet

Magnetic Fields

• Magnets produce magnetic forces and have magnetic

field lines

• The magnetic force is that force of attraction or repulsion

between magnets

• The magnetic field is the area of space in which the

magnetic force can work on another magnet

Mapping Magnetic Fields

• Rules:

– The magnetic field lines can never cross

– Always flow from North to South

– The closer the lines, the stronger the attraction

– The lines near the poles are closer to one another

because the poles have the greatest magnetic

intensity

Draw in the magnetic field lines

Draw in the magnetic field lines

Compass

– The needle of the compass is a small bar

magnet free to turn on a pivot

– Red (or any color) tip of the needle is

considered North and will always be attracted

towards its opposite the South

• Because the needle of a compass is a small magnet we

can use it to identify the poles of another magnets.

• When a compass is placed next to another magnet, the

north pole of the compass will point to the south pole of

the magnet (also indicating the direction of the magnetic

field lines)

Electromagnetism – straight line

conductor (AKA a wire)

• Electricity and Magnetism – how are they related?

• When an electric current passes through a wire a

magnetic field is formed.

• Have a North and a South pole

• They have a circular magnetic field

Straight Line Conductor – Right Hand

Rule

• Point your thumb in the direction of conventional current

(toward the negative terminal.)

• The direction that your fingers wraps around the wire

show the direction of the magnetic field lines -- the hand

may either be in front or behind, depending on where the

negative post is found

– These lines are circular

• Your fingernails always point South and your knuckles

point North If you place a compass near the wire, the

north pole of the compass will point in the direction of

your finger nails (the same direction as the arrows)

• South and North will be found above or below the

straight line conductor – NEVER at the ends

Because the field is

circular, the

direction of the

compass depends

on where the

compass is located

in relation to the

wire

Practice

+

I

+

-

I

-

Current flow into the paper Current flow out the paper

+

-

+-

Practice

+

-

Show the direction the compass will point if placed in that position

The direction of the

compass is the

same as the

magnetic field lines

at the same

position