What is a magnetic field?
Topic: Electricity and magnetism
Answer: A magnetic field is the region around a magnet where magnetic forces can act.
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What can a magnetic field exert a force on?
Topic: Electricity and magnetism
Answer: It can exert a force on another magnetic field, such as the field around another magnet or a current-carrying coil.
How can magnetic field lines be used to show a magnetic field?
Topic: Electricity and magnetism
Answer: They show the direction and pattern of the magnetic field. Closer field lines show a stronger field.
What direction do magnetic field lines point outside a bar magnet?
Topic: Electricity and magnetism
Answer: They point from the north pole to the south pole outside the magnet.
Where is the magnetic field strongest around a bar magnet?
Topic: Electricity and magnetism
Answer: It is strongest near the poles, where the field lines are closest together.
What happens when two north poles are brought together?
Topic: Electricity and magnetism
Answer: They repel each other because like poles repel.
What happens when a north pole and a south pole are brought together?
Topic: Electricity and magnetism
Answer: They attract each other because unlike poles attract.
How can a compass show the direction of a magnetic field?
Topic: Electricity and magnetism
Answer: The compass needle lines up with the magnetic field, so its north-seeking end points along the field direction.
What is an electromagnet?
Topic: Electricity and magnetism
Answer: An electromagnet is a magnet produced by an electric current, usually made stronger by a coil of wire around an iron core.
How can a simple electromagnet be made?
Topic: Electricity and magnetism
Answer: Wrap insulated wire into a coil around a soft iron nail or core, then connect the wire to a cell or power supply so current flows.
Why is insulated wire used in an electromagnet coil?
Topic: Electricity and magnetism
Answer: The insulation prevents neighbouring turns of wire from short-circuiting while still allowing the coil to be wound closely.
Why is a soft iron core useful in an electromagnet?
Topic: Electricity and magnetism
Answer: Soft iron becomes strongly magnetised when current flows and loses most of its magnetism when the current is switched off.
What is one major advantage of an electromagnet over a permanent magnet?
Topic: Electricity and magnetism
Answer: An electromagnet can be switched on and off by controlling the current.
Name three applications of electromagnets.
Topic: Electricity and magnetism
Answer: Electromagnets are used in scrapyard lifting cranes, electric bells, relays, loudspeakers and magnetic door locks.
Why are electromagnets useful in scrapyard cranes?
Topic: Electricity and magnetism
Answer: The magnet can be switched on to pick up magnetic metals and switched off to release them.
How does increasing the number of turns on the coil affect an electromagnet?
Topic: Electricity and magnetism
Answer: More turns usually make the electromagnet stronger if the current and core stay the same.
How does increasing the current affect an electromagnet?
Topic: Electricity and magnetism
Answer: A larger current usually makes the electromagnet stronger, but too much current may heat the wire.
How does adding an iron core affect a coil electromagnet?
Topic: Electricity and magnetism
Answer: An iron core makes the magnetic field much stronger than an air core.
What variable could be changed to investigate electromagnet strength?
Topic: Electricity and magnetism
Answer: The number of coil turns, the current, the number of cells, or the core material could be changed.
What variables should be controlled when testing the effect of coil turns?
Topic: Electricity and magnetism
Answer: Keep the same core, wire, current or number of cells, measuring method and time switched on.
How can the strength of an electromagnet be measured simply?
Topic: Electricity and magnetism
Answer: Count the number of identical paper clips it can pick up, or measure the maximum distance from which it can attract a small magnetic object.
Why should the same paper clips be used in an electromagnet investigation?
Topic: Electricity and magnetism
Answer: Different sizes or materials would change how easily they are attracted, making the test unfair.
Why should an electromagnet not be left switched on for too long?
Topic: Electricity and magnetism
Answer: The wire and cell can heat up, which may damage equipment and affect the results.
What happens to an electromagnet when the current is switched off?
Topic: Electricity and magnetism
Answer: The magnetic field from the current disappears, and a soft iron core loses most of its magnetism.
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