8J Magnets and Electromagnets KS3 Physics 8J Magnets and Electromagnets

8J Magnets and Electromagnets Contents 8J Magnets and Electromagnets Magnetic materials Magnetic fields Electromagnets Summary activities

Magnetic materials cobalt (Co) gold (Au) iron (Fe) nickel (Ni) Which of the metals below are magnetic metals? cobalt (Co) gold (Au) iron (Fe) nickel (Ni) copper (Cu) zinc (Zn) magnesium (Mg) aluminium (Al) silver (Ag)

Magnetic materials S N Ni Fe Co Au Mg Cu Zn Al Ag A magnetic material is attracted to a magnet. Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic. N S Fe Ni Co Al Zn Ag Cu Au Mg

Magnetic or non-magnetic?

8J Magnets and Electromagnets Contents 8J Magnets and Electromagnets Magnetic materials Magnetic fields Electromagnets Summary activities

Forces between magnets – experiment

What is a magnetic field? The region around a magnet where it has a magnetic effect is called its magnetic field. When a magnetic material is placed in a magnetic field it will experience a force. S N The iron filings feel the effect of the magnetic field and show the direction of the forces in this region.

Shape of a magnetic field What is the shape and direction of the lines of force in the magnetic field around a bar magnet? strongest field at poles strongest field at poles N S weakest field further away from poles Where is the magnetic field strongest?

Viewing magnetic fields: N poles together Bring the north poles of two bar magnets together. What happens to the magnets? S N N S Next, bring the two north poles as close to each other as possible and place a piece of paper on top of the magnets. Carefully scatter iron filings onto the paper. Draw the pattern created by the iron filings.

Magnetic field pattern: N poles together What do you notice about the pattern of the lines of force in the region between the two north poles? S N N S

Viewing magnetic fields: N and S poles together Bring the north and south poles of two bar magnets together. What happens to the magnets? S N S N Next, put the north and south poles close to each other, without letting them touch, and place a piece of paper on top. Carefully scatter iron filings onto the paper. Draw the pattern created by the iron filings.

Magnetic field pattern: N and S poles together What do you notice about the pattern of the lines of force in the region between the north and south poles? S N S N How does this pattern compare with the pattern between the two north poles?

Magnetic fields – summary 1. When two like poles (e.g. two north poles or two south poles) are put together, they repel each other. 2. When two unlike poles (e.g. a north and a south pole) are put together, they attract each other. 3. Scattering iron filings around a bar magnet makes it possible to see the lines of force of the magnetic field.

There are three methods that can be used to make a magnet: Making a magnet A magnet can be made by magnetizing a material which is attracted to a magnet, e.g. a paper clip. There are three methods that can be used to make a magnet: Stroke a magnet along the paperclip from one end to the other and then starting from the same place, repeat the movement. The more times this is done, the more magnetic the clip becomes. Hold a nail in a magnetic field and hit it with a hammer. Put a magnetic material in a strong magnetic field.

8J Magnets and Electromagnets Contents 8J Magnets and Electromagnets Magnetic materials Magnetic fields Electromagnets Summary activities

Making an electromagnet When electricity is passed through a coil of wire, the coil has a magnetic field around it. This is called an electromagnet. If the coil of wire is wrapped around a piece of iron, such as an iron nail, the magnetic field gets stronger.

Investigating an electromagnet An iron core at the centre of a coil of wire increases the strength of an electromagnet. Two experiments can be carried out to investigate the other factors that can affect the strength of an electromagnet: 1. Investigate how the number of coils affects the number of paper clips attracted to an electromagnet – keep the current the same in this experiment. 2. Investigate how the size of the current affects the number of paper clips attracted to an electromagnet – keep the number of coils the same in this experiment.

Investigating an electromagnet – results 1 8 18 31 46 Remember – keep the current the same throughout this experiment!

Investigating an electromagnet – results 2 12 23 38 49 60 Remember – keep the number of coils the same throughout this experiment!

Investigating an electromagnet – graph 1 number of clips attracted number of coils

Investigating an electromagnet – graph 2 number of clips attracted current (A)

Using electromagnets – scrap yards A large electromagnet is used in a scrap yard to pick up and move heavy pieces of scrap metal. Which metals would the electromagnet attract? What advantages does an electromagnet have over a permanent magnet?

Using electromagnets – door bells The circuit for a door bell includes an electromagnet.

Using electromagnets – relay Lifts, cars and other large electrical machines use high currents. A relay, which includes an electromagnet, is used to allow a small current in one circuit to control a large current in another circuit.

Label the diagram – electric bell

Label the diagram - relay

Electromagnets – summary 1. When electricity is passed through a coil of wire, the coil behaves like a magnet and has a magnetic field around it – this is an electromagnet. 2. There are three ways to make an electromagnet stronger: wrap the coil of wire around an iron core; increase the number of coils; increase the size of the current. 3. An electromagnet can be easily turned on and off. This is why electromagnets can be used in scrapyards and as switches in electrical devices.

8J Magnets and Electromagnets Contents 8J Magnets and Electromagnets Magnetic materials Magnetic fields Electromagnets Summary activities

attraction – The force that pulls things together, Glossary attraction – The force that pulls things together, e.g. opposite poles of two magnets. electromagnet – A magnet made by passing electricity through a coil of wire, which often has a core inside. magnet – An object that has a magnetic field and can attract magnetic materials. magnetic field – The area around a magnet where its magnetic force can be felt. magnetic materials – Materials that are attracted to a magnet, e.g. iron, cobalt and nickel. magnetism – The non-contact force of a magnetic field. poles – The parts of a magnet where its magnetic field is strongest. repulsion – The force that pushes things away from each other, e.g. like poles of two magnets.

Anagrams

Magnetism – true or false?

Multiple-choice quiz