Magnetic Fields (Oxford AQA IGCSE Physics)

Magnetic Fields

• A magnetic field surrounds all magnets

• A magnetic field is defined as:

The space around a magnet where a force acts on another magnet or a magnetic material (such as iron, steel, cobalt and nickel)

Magnetic field lines

• Magnetic field lines represent:

  • The strength of the magnetic field

  • The direction of the magnetic field

• The spacing of field lines shows the strength of the field

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

  • When the field lines are further apart, the field is weaker

• Field lines always have an arrow indicating the direction of the field line

  • The direction of the field line shows the direction that the magnetic force would act

  • The field lines always go from a north pole to a south pole

Uniform magnetic field

• A uniform magnetic field is where the field lines are equally spaced

  • All act in the same direction

  • Show the same strength at every point

• A uniform magnetic field can be found between the opposite poles of two bar magnets or inside a solenoid

Uniform magnetic field

Magnetic field around one bar magnet

• The magnetic field is strongest at the poles

  • Therefore, the magnetic field lines are closer together

• The magnetic field becomes weaker as the distance from the magnet increases

  • Therefore, the magnetic field lines get further apart

Magnetic field around a bar magnet

Magnetic field around two bar magnets

• Two bar magnets can repel or attract, the field lines will look slightly different for each

• Two attracting bar magnets placed end to end have:

  • A uniform field going from north to south between the nearby poles

  • Further away from the magnets, the field lines get further apart

• Two repelling bar magnets placed end to end have:

  • Field lines going into the south poles or out of the north poles and not connecting at the nearest side

  • This creates a space between the magnets where there is no field present

Magnetic field around two bar magnets placed end to end

• In a less common side-by-side configuration, the field lines still show attraction between opposite poles and repulsion between like poles

Magnetic field around two bar magnets placed side to side