Course: Combined Science + Separate Physics | Tier: Foundation + Higher
Notes
Poles and forces
The poles of a magnet are where the magnetic forces are strongest. When two magnets are close, they exert a non-contact force on each other: like poles repel and unlike poles attract.
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- A permanent magnet produces its own magnetic field.
- An induced magnet is a material that becomes a magnet when it is placed in a magnetic field. It loses most or all of its magnetism when removed from the field.
- Induced magnetism always causes a force of attraction.
- A magnetic field is the region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel).
- The field is strongest at the poles and gets weaker with distance from the magnet.
- Field lines point from the north pole to the south pole.
Plotting a field with a compass
A compass contains a small bar magnet, so it points in the direction of the magnetic field. Place the compass near the magnet, mark where the needle points, move the compass to that mark, and repeat. Join the dots to draw a field line. Field lines closer together mean a stronger field.
The Earth’s magnetic field
Away from any magnets, a compass points north. This is evidence that the Earth’s core is magnetic and produces its own magnetic field.
Questions
Q1 (F) What happens when two north poles are brought close together?
Show answer
They repel (push each other away).
Q2 (F) Name the four magnetic materials.
Show answer
Iron, steel, cobalt and nickel.
Q3 (F) What is the difference between a permanent magnet and an induced magnet?
Show answer
A permanent magnet produces its own magnetic field all the time. An induced magnet only becomes a magnet when it is in a magnetic field, and loses most or all of its magnetism when removed.
Q4 (F) Where is the magnetic field of a bar magnet strongest?
Show answer
At the poles.
Q5 (F/H) A steel paperclip is attracted to both the north and the south pole of a magnet. Explain why.
Show answer
The paperclip becomes an induced magnet when it is in the magnet’s field. Induced magnetism always causes attraction, whichever pole is nearest.
Q6 (F/H) Describe how to use a compass to plot the magnetic field around a bar magnet.
Show answer
Put the magnet on paper. Place a compass near one pole and mark the direction the needle points. Move the compass so its tail is at the mark and mark again. Repeat until you reach the other pole, then join the marks and add an arrow from north to south. Repeat from different starting points.
Q7 (H) What evidence is there that the Earth has a magnetic core?
Show answer
A compass points north when it isn’t near any other magnet, so the Earth must have its own magnetic field.
