9.5Physics 03. Electricity And Magnetism
Magnetic fields making an electromagnet factors affecting… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions
5 min read 11 parts Lesson 5 of 5 1 quiz
9.5 Magnets, magnetic fields and electromagnets — CHECKPOINT - Lower Secondary Science 0893 notes: Describe magnetic fields, how to make an electromagnet and the factors that affect its strength.Magnet — an object that attracts magnetic materials.Magnetic materials include iron, …
- Forces between poles
- Detecting a field
- Iron filings
- Rules for drawing
- Between magnets
- Switching off
Section 1 of 11Magnets and magnetic materials
- Magnet
- an object that attracts magnetic materials.
- Magnetic materials include iron, steel, nickel and cobalt.
- Poles
- every magnet has a north pole and a south pole.
- Forces between poles
- like poles repel and unlike poles attract.
Section 2 of 11Magnetic field
- Magnetic field
- the area around a magnet where its effects can be detected.
- It is strongest at the poles.
- Detecting a field
- a magnetic object is attracted, or the needle of a compass turns to point along the field.
- Iron filings
- scattered on paper above a magnet, they show the pattern of the field.
Section 3 of 11Magnetic field lines
- Rules for drawing
- the lines join opposite poles, have arrows pointing from north to south, and never touch or cross.
- Strength
- the field is strongest where the lines are closest together.
- A stronger magnet has lines that are closer together and extend further away.
- Between magnets
- lines run in the same direction between unlike poles, which attract, and in opposite directions between like poles, which repel.
Section 4 of 11Permanent magnets and electromagnets
| Feature | Permanent magnet | Electromagnet |
|---|---|---|
| Field | Always present | Present only when current flows |
| Switching | Cannot be switched off | Can be switched on and off |
| Made by | Magnetising a magnetic material | Current in a coil around a magnetic core |
Section 5 of 11Making an electromagnet
- Wrap insulated wire tightly around an iron nail to form a coil.
- Leave enough wire at each end to connect to a cell and a switch.
- Connect the coil in a circuit with the cell and the switch.
- Close the switch and test whether the nail picks up paperclips.
- Parts
- the wire wrapped in a coil, a magnetic core in the middle of the coil and a current in the coil.
- Switching off
- when the current stops the core loses most of its magnetism.
Section 6 of 11Poles of an electromagnet
- Finding the poles
- a compass or a bar magnet with known poles shows which end is north or south.
- Reversing the poles
- wrap the coil the opposite way or reverse the connections to the cell.
Section 7 of 11Factors affecting the strength
| Factor | Effect on strength |
|---|---|
| Number of turns in the coil | More turns give a stronger electromagnet |
| Current in the coil | A greater current gives a stronger electromagnet |
| Material of the core | Soft iron gives a stronger electromagnet than steel |
Section 8 of 11Investigating the strength
- Change only one factor, such as the number of turns.
- Keep the other factors, including the current and the core, the same.
- Count the number of paperclips that the electromagnet picks up.
- Repeat and calculate the mean.
Section 9 of 11Uses of electromagnets
- Fire doors held open by an electromagnet connected to the fire alarm.
- Sorting scrap metal and lifting iron and steel.
- Toasters, electric bells, electric motors and MRI scanners.
Section 10 of 11Key terms
| Term | Meaning |
|---|---|
| Magnetic field | Area around a magnet where its effects can be detected. |
| Electromagnet | A magnet made by current in a coil around a magnetic core. |
| Core | The magnetic material in the middle of a coil. |
| Permanent magnet | A magnet whose field is always present. |
| Compass | Instrument with a magnetised needle that points along a magnetic field. |
| Coil | Wire wound into loops. |
Section 11 of 11Exam technique
- All metals are magnetic — only iron, steel, nickel and cobalt are.
- Magnetic and magnetised mean the same — magnetic materials can be turned into magnets.
- An electromagnet works without current — it needs a current in the coil.
- Field lines are real lines — they represent the magnetic field.
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