Magnetism
Property of Magnets
•We say that unlike poles attract, andlike poles repel.
Magnetic field
•Magnets createmagnetic fields.
•These cannot be seen.
•They are the spacearound a magnet overwhich it has a magneticeffect.
Distinguish between:
a magnet
a magnetic material
a non magnetic material?
Produces a magnetic field
Reacts to a magnetic field
Doesn’t react to a magnetic field
To investigate the magnetic field ofa magnet and plot it.
•Small compasses called plotting compasses can beused to show the magnetic field around a barmagnet
•When plotting compasses are put around a barmagnet, the needles point away from the magnet'snorth pole and towards its south pole.
To investigate the magnetic field ofa magnet and plot it
•Put a plotting compass on the north pole of the magnet
•With a pencil mark the positions of both ends of theneedle of the plotting compass
•Move the compass so that the south pole on thecompass is now at the point where the north pole was.
•Continue this until you reach the south pole.
•Join the dots
weakest field furtheraway from poles
N
S
Strength of a magnetic field
strongestfield
at poles
strongestfield
at poles
The magnetic field of a bar magnet
N
N
S
S
Magnetic field pattern: Npoles together
What do you notice about the pattern of the lines of forcein the region between the two north poles?
The earths magnetic field
The Earth does not contain a giant bar magnet, but itbehaves as if it does.
The Earth has a magnetic pole in the north and onein the south.
.
How a compass works
•The small magnet inside a compass feelsthe earths magnetic force and alwayspoints toward the south magnetic poleof the earth ( but we call it the north pole!)
Uses of magnets
The Maglev Trains in Japan use magnetic repulsion totrain to “float” above the track
Magnets used to sort metal in aship yard
Orienteering
•A magnetic compass helps us in directionfinding.
•Compasses always points towards northpole ( but this is actually the southmagnetic pole )
Do you know…
1.How magnets behave when they come into contactwith each other
2.What a magnetic field is
3.How to plot the magnetic field of a magnet
4.How a compass works
5.Some uses of magnetic fields
