Study notes
Magnets
Magnets are objects that can attract magnetic materials and exert magnetic forces of attraction and repulsion on other magnets.
Learn it step by step
Magnetic and Non-Magnetic Materials
Magnets can only attract materials made of magnetic metals such as iron, steel, nickel, and cobalt. Non-magnetic materials like wood, plastic, glass, copper, and aluminium are not attracted by magnets.
| Magnetic Materials | Non-Magnetic Materials |
|---|---|
| Iron | Wood |
| Steel | Plastic |
| Nickel | Aluminium |
| Cobalt | Copper |
Magnetic Poles and Direction
Every magnet has two poles, a North-seeking pole (N-pole) and a South-seeking pole (S-pole). When freely suspended, a magnet will always come to rest in a North-South direction.
Magnetic Force is Strongest at the Poles
The magnetic attraction is strongest at the two poles of a magnet and weakest at the middle. This is why most paper clips stick to the ends of a bar magnet rather than its center.
Attraction and Repulsion
Like poles repel each other (N-pole repels N-pole, S-pole repels S-pole), while unlike poles attract each other (N-pole attracts S-pole). Repulsion is the only sure test to confirm if an unknown object is a magnet.
Magnetic Force Acts from a Distance and Through Materials
Magnetic force is a non-contact force that can pull or push objects without touching them. Magnetic force can also pass through non-magnetic materials like paper, cardboard, and thin plastic sheets.
Making and Caring for Magnets
Magnetic objects can be turned into temporary magnets using the stroke method (stroking in one direction with one pole) or the electrical method (coiling wire around an iron rod connected to a battery). Magnets can lose their magnetism if dropped, hammered, or heated.
Worked examples
- Recall that a magnet attracts both opposite magnetic poles and all magnetic materials.
- Object X could be a magnet with its South pole facing the bar magnet, or it could simply be a non-magnetised magnetic material like a piece of iron.
- State the conclusion clearly: Mandy is incorrect because repulsion is the only sure test for a magnet. Attraction can happen between a magnet and a magnetic material.
- Hold the iron nail firmly.
- Stroke the entire length of the nail with only one pole of the bar magnet in one direction repeatedly, at least 20 to 30 times.
- Lift the magnet clear of the nail after each stroke before starting the next stroke.
- Identify the material of the table: Wood is a non-magnetic material.
- Apply the property of magnetism: Magnetic force can pass through non-magnetic materials.
- Conclude that the magnet's force passes through the wooden tabletop to attract the steel paper clip underneath.
- Recall the factors affecting electromagnet strength: the number of wire coils and the amount of electric current.
- State the first way: Increase the number of turns or coils of wire around the iron rod.
- State the second way: Increase the number of batteries to provide more electric current.
Mind map
Mind map for Magnets.
- Properties
- Has two poles: North and South
- Strongest magnetic force at poles
- Freely suspended magnet rests in North-South direction
- Interactions
- Like poles repel
- Unlike poles attract
- Repulsion is the only sure test
- Materials
- Magnetic: Iron, Steel, Nickel, Cobalt
- Non-magnetic: Wood, Plastic, Glass, Copper, Aluminium
- Force passes through non-magnetic materials
- Making Magnets
- Stroke method in one direction
- Electrical method with wire coil and battery
- Caring for Magnets
- Store with keepers in pairs
- Avoid dropping, hammering, or heating