Magnets

Interactions

Magnets

by Teacher Shan

​Magnetic Materials

​- A magnet can attract (or pull) a magnetic material

​- A magnetic material is a material that can be attracted by a magnet.

- Only a few metals are magnetic materials:

​1. Iron

​2. Nickel

​3. Cobalt

​4. Steel

​Non-magnetic Materials

​Materials that cannot be attracted by a magnet are called non-magnetic materials.

​- All non-metals such as glass, wood, plastic, clay and rubber

​- Other metals such as aluminium, zinc, copper and others

​

​*Not all metals are magnetic materials

Shapes of Magnets

​Magnetic Strength

• ​The magnetic strength of a magnet is different at different positions of the magnet

• ​The magnet strength becomes weaker further away from the poles

• ​The magnetism is the strongest at these 2 poles

• ​The magnetism is the weakest in the middle of the magnet

Magnetic Strength

​Test: The number of iron nails attracted at four different positions, A, B, C and D of the bar magnet was counted and recorded in the table below.

​

​Results: The magnetism of the bar magnet is the strongest at its poles. Its magnetic strength becomes weaker away from its poles.

​A freely suspended magnet will always come to rest at the North-South direction

​Magnetic Forces: Attraction

• ​Attraction (Unlike Poles)

• ​The North Pole and the South Pole

• ​Unlike Poles attract to each other (pull towards)

​Magnetic Forces: Repulsion

• ​Repulsion (Like Poles)

• ​The North Pole and the North Pole

• ​The South Pole and the South Pole

• ​Like Poles repel from each other (push away from each other)

​Ring Magnets

​Ring Magnets are used to show the attraction and repulsion of magnets due to like or unlike poles.

In the diagram below, three-ring magnets are placed together in a plastic rod.

Each ring magnet has 2 poles (North and South Pole)

​Ring Magnets

​When the unlike poles face each other, both

ring magnets attract.

​

​When the like poles face each other, both

ring magnets repel each other

Multiple Select

Sam carried out an experiment as shown. He noticed that magnet X floated above magnet Y. Based on the set-up, which of the following statements are definitely correct?

• Magnetic force acts at a distance

• The like poles of the ring magnets face each other

• The magnetic strength of ring magnet X is weaker than that of ring magnet Y

​Types of Magnets

​1. Temporary (short time); Electromagnet is used in fire alarms or electric bells, in scrap yards or landfills sites to separate useful metals from non-metals

​2. Permanent (long time);

​Permanent magnets are used in the fridge door, compass needle, magnetic door catch and in loudspeakers or television

Electromagnets

​- An iron bar (or any objects made of iron) is coiled around by electrical wire

​- The electrical wire is connected to an electric supply such as a battery

​the iron bar will become a temporary magnet when electricity is turned on

​Factors affecting the strength of an electromagnet:

​- The number of turns or coils around the iron bar

​- The amount of electricity flowing in the circuit

Stroking Magnet