Magnetism & Electromagnetism - 7.1.2 Magnetic Fields (GCSE Physics AQA)

Magnetic Fields

Defining Magnetic Fields

AQA exams may ask you to define the term ‘magnetic field’. Here’s a simple definition to answer those types of questions.

The magnetic field is the region around a magnet where a force acts on another magnet or magnetic material (iron, steel, cobalt and nickel).

Forces in Magnetic Fields

• Magnets exert forces. We have mentioned this several times before, but it is important to remember that the poles of a magnet will exert forces. These forces can either be a force of attraction or a force of repulsion.
• Magnetic materials experience forces. When we place a magnet next to certain materials, they will experience a force of attraction. These certain materials are known as magnetic materials. They will always be attracted to magnets.

Strength of Magnetic Fields

• Distance is important. The distance in between the magnet and the magnetic object is very important when determining the strength of the magnetic field. The closer we hold an object to the magnet, the stronger the magnetic field will be.
• The field strength is strongest at the poles. As we discussed previously, the magnetic field is strongest at the poles of the magnet. This means that if an object is placed close to the pole of a magnet, then it will experience a stronger magnetic field than if it was simply placed to the side.

Direction of Magnetic Fields

• We can find the direction of a magnetic field. We can find the direction of a magnetic field quite simply by using force. This ‘force’ is the force that will act on the north pole of the magnet from that point.

• Magnetic field lines run from north to south. If we take a bar magnet (or any permanent magnet), we can plot the field lines around the magnet. These field lines will denote the shape of the magnetic field. The important thing to remember is that these field lines will run from the north pole of the magnet to the south pole of the magnet.

Magnetic Compass

• A magnetic compass has a bar magnet.
• Compasses use the Earth’s magnetic field.

Drawing Magnetic Fields

We can draw magnetic fields in one of two ways; by using a bar magnet, or by using a magnetic compass. We’ll explore these in more detail in this section.

Using a Bar Magnet

Using a Magnetic Compass

1. Place a bar magnet onto a piece of paper and draw around it. Label one end North, and the other end as South.
2. Place a magnetic compass on the paper. Make sure that the compass is close to the North Pole of the magnet. On the piece of paper, draw on a small arrow in the direction that the compass is pointing.
3. Move the magnetic compass away from the North Pole, towards the South pole. Continue to mark the arrows onto the piece of paper.
4. You should end up with a series of arrows running from North-South. Repeat this at various points around the magnet, until you get a diagram like the one shown.

Behaviour of A Magnetic Compass

• Magnetic compasses rely on the Earth.
• The Earth is magnetic.