Magnetism and Magnetic Fields

Magnetic Fields

Magnetic Field: Definition

The region around the magnet where magnetic materials experience a force

(feels pulled towards the magnet)

Seeing magnetic field patterns with iron fillings

• We cannot see the magnetic field of a magnet, but we can see the effect of the field on magnets or magnetic materials

• To do this we can use iron fillings

Seeing magnetic field patterns with iron fillings

• Iron fillings are very small pieces of iron that become magnetised when they are in a magnetic field

• When magnet is brought around iron fillings, they will line up at every point where they feel the force from the magnet

• Because there are so many of them, they line up until we can see the shape of the magnetic field.

Open Ended

Checkpoint 1: Where is the magnetic field of a bar magnet strongest and how do you know?

Magnetic field around two magnets that repel each other (same pole facing each other)

Notice that the region in the middle between the two magnets is empty. The point in the middle of this region is called the neutral point - where the magnetic fields of the two magnets cancel out.

Multiple Choice

What would happen if you put a small steel ball at the neutral point?

• It will move towards either one of the magnets

• It gets magnetised

• Nothing happens

Seeing magnetic field patterns with a plotting compass

• A compass always points towards the North because its needle is a small magnet and it lines up with the Earth's magnetic field

• When magnet is brought around a compass, the needle will line up with the magnetic field of the magnet rather than the Earth's magnetic field

• The direction is from north to south

Drawing the magnetic field lines around a magnet

• The strength of the magnetic field is indicated by the spacing of the field lines

• If the field is stronger, the lines are closer together

• The arrows on the line show the direction of the force. Magnetic field lines go from the north pole to the south pole.

Multiple Choice

Where is the magnetic field the strongest around a bar magnet?

• far away from the magnet

• at the side of the magnet

• at the poles

• above the magnet

The Earth's magnetic field

The magnetic field of the Earth looks similar to that of a bar magnet

The compass needle point to the North, which is actually the magnetic south pole of the Earth

Multiple Choice

What is the shape of a magnetic field around the Earth?

Multiple Choice

The area of magnetic force around a magnet is known as its _____________.

• magnetic field

• magnetic declination

• magnetic fan lines

• magnetic tan lines