Magnetic Fields (Cambridge International IGCSE Physics)

Spec point — 4.1.3 · - Describe a magnetic field as a region in which a magnetic pole experiences a force

• Draw the pattern and direction of magnetic field lines around a bar magnet
• State that the direction of a magnetic field at a point is the direction of the force on the N pole of a magnet at that point

Magnetic fields

• A magnetic field is defined as:

A region in which a magnetic pole experiences a force

Magnetic field around a bar magnet

• The magnetic field is strongest at the poles

  • Therefore, the magnetic field lines are closer together at the ends of the magnets

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

  • Therefore, the magnetic field lines get further apart

Magnetic field lines are directed from the north pole of a magnet to the south pole

Magnetic field lines

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

  • The direction of the field line shows the direction in which the magnetic force would act
  • The field lines always go from a north pole to a south pole

Magnetic field strength

Spec point — 4.1.3 · - Explain that magnetic forces are due to interactions between magnetic fields

• Know that the relative strength of a magnetic field is represented by the spacing of the magnetic field lines

Magnetic field strength

Extended Tier Only

• Magnetic forces are due to interactions between magnetic fields

  • Two bar magnets can repel or attract

• This is shown by the magnetic field lines between the two magnets:

Attractive and repulsive magnetic fields

Magnetic field lines for attracting and repelling bar magnets

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

  • If the magnetic field lines are close together then the magnetic field will be strong
  • If the magnetic field lines are far apart then the magnetic field will be weak

Exam Hint If you are asked to draw the magnetic field around a bar magnet remember to indicate both the direction of the magnetic field and the strength of the magnetic field. You can do this by:

• adding arrows pointing away from the north pole and towards the south pole
• making sure the magnetic field lines are further apart as the distance from the magnet increases