Grade 9 · Electricity and Magnetism · Circuits and Current
Magnetism and Electromagnets
Magnetic fields, and how electricity makes a magnet you can switch off.
Learning objectives
- Describe magnetic field patterns.
- Explain how an electromagnet works.
- Investigate factors affecting electromagnet strength.
NGSS alignment
MS-PS2-5
Conduct an investigation and evaluate the experimental design to provide evidence that fields exist between objects exerting forces on each other even though the objects are not in contact.
HS-PS2-5
Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.
MS-PS2-3
Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion B — Inquiring and Designing
ENGAGE
The crane that drops a car on command
A scrapyard crane lifts a car with a magnet, moves it, then releases it instantly with the flick of a switch.
Think about it
- Why would a permanent magnet be useless here?
- What does the switch actually change?
EXPLAIN
Fields and electromagnets
A magnetic field is the region where a magnetic material experiences a force. Field lines run from north to south, and closer lines mean a stronger field.
- Like poles repel, unlike poles attract
- Magnetic materials include iron, cobalt, nickel and steel
- A current in a wire produces a magnetic field around it
- A coil (solenoid) with an iron core makes a strong electromagnet
| Change | Effect on electromagnet strength |
|---|---|
| More turns on the coil | Stronger |
| Larger current | Stronger |
| Adding an iron core | Much stronger |
| Switching the current off | Magnetism disappears |
Why it matters
Electromagnets can be switched, reversed and varied, which makes motors, loudspeakers, relays, MRI scanners and maglev trains possible.
INVESTIGATION
What makes an electromagnet stronger?
research question
How does the number of coil turns affect the number of paper clips an electromagnet can hold?
hypothesis
More turns will hold more paper clips because each turn adds to the magnetic field.
variables
Independent: number of turns (20, 40, 60, 80, 100). Dependent: number of paper clips held. Controlled: current, same iron nail, same paper clips, same wire.
method
Wind the coil around an iron nail, connect to a low-voltage supply with a fixed current, and count the paper clips picked up. Repeat three times per coil and take a mean.
safety
Use a low voltage and switch off between trials; the wire warms quickly.
analysis
Plot mean clips against turns and describe the trend. Suggest one improvement to control the current more precisely.
Watch
Magnetism: Crash Course Physics
CrashCourse · 10 min
Links electric current to magnetic fields.
Before you watch: Why can an electromagnet be switched off?
- Name two ways to strengthen an electromagnet.
- Describe the field around a bar magnet.
Interactive simulation · PhET
Faraday's Law
Move the magnet through the coil and watch the bulb. Try more coil turns.
While you explore
- What must happen for a current to be induced?
- How do more turns change the effect?
Key vocabulary
- Electromagnet
- A magnet made by passing current through a coil.
- Magnetic field
- The region where a magnet can exert a force.
Practice questions
0/2 correct
Level 1 · Criterion A
Which change makes an electromagnet stronger?
Level 2 · Criterion A
The main advantage of an electromagnet over a permanent magnet is that it:
MYP criterion tasks
Level 3 · Criterion B
Plan how you would test whether current or the number of coil turns has a greater effect on electromagnet strength.
Reflect & track
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