SPH3U: Electricity Intro to Magnetism

Magnetic Poles Every magnet has a north and south pole  Like Poles Repel  Opposite Poles Attract SNNSNSNS

Magnetic Field The magnetic field around a magnet is strongest at the poles. The north pole and the south pole of the same bar magnet are in general, equally strong. If you cut a magnet in two pieces, each piece will have a north and south pole. You can keep cutting to make smaller and smaller magnets – but each one will be weaker in strength.

Magnetic Field Physicists are currently doing research to see if it is possible to get a monopole magnet – one in which there is only a north pole, or only a south pole. Do you think this is possible? A magnetic field is the space around a magnet where a magnetic force can be felt. It is very similar in theory to an electric field.

Properties of the Magnetic Field Most materials will respond at least a little bit to a magnetic field, but only a very small bit. Materials that respond very strongly to a magnetic field are called ferromagnetic. Some examples of ferromagnetic materials are: - Iron - Nickel - Cobalt

Lines of Magnetic Force Draw in the pattern you see with the iron filings  These are the lines of magnetic force S N

Lines of Magenetic Force Lines of magnetic force show how the magnetic force acts around the magnet. The force is strongest at the poles (where the lines are close together) and weaker the further out you go.

Lines of Magenetic Force When a compass is places upon a line of force, the compass needle always points along the line. The north pole of the compass is directed toward the south pole of the magnet.

Lines of Magenetic Force The direction of a line of force is defined as the direction in which the north pole of a compass points when placed along that line.

Lines of Magenetic Force Even though we draw the lines on a flat sheet, it is important to note that the lines exist in 3-dimensions.

Lines of Magnetic Force A horseshoe magnet

Lines of Magnetic Force When drawing Magnetic Field lines, remember: Lines go from North to South outside the magnet Lines go from South to North inside the magnet Lines never cross

Practice Draw the magnetic field lines

Predicting Magnetic Forces Lines of force that act in the same direction will make the magnetic force stronger.

Predicting Magnetic Forces Lines of force that act in the opposite direction will make the magnetic force weaker.

Predicting Magnetic Forces Parallel fields from two different magnets show us that there is a repulsion.

Predicting Magnetic Forces Opposite fields from two different magents show us that there is an attraction.

The Earth The Earth has a magnetic field, which can be detected by a compass. The magnetic field around the earth is actually not the way we would think of it. The geographical North pole actually works the same way as the south pole of a magnet.

The Earth

Homework Read section 12.1 (pages ). Make your own summarized notes of the practical applications of magnets in industry, and magnetism in the natural world (pg ). Make sure you can describe in detail at least 3 applications of magnets. Answer questions #1-6 on page 552