Lesson 3 of 6 · Magnetism
The Motor Effect
🧲
🎯 Your mission
Run the experiment. Find out what really happens.
⚡ The twist
The opposite of what you expect is often what happens.
What you'll learn
A current-carrying wire in a magnetic field experiences a force perpendicular to both, given by F = BIL. Fleming's left-hand rule gives the direction. Reverse either the current or the field and the force reverses — this is what turns an electric motor.
Key words
motor effect
The force on a current-carrying conductor placed in a magnetic field.
Fleming's left-hand rule
A rule giving the direction of force, field and current in a motor.
Make a hypothesis first
Predict: what happens if you double the force?
Say your guess out loud — then find out if you were right.
Get ready
🧰 What you need
- strong horseshoe magnet
- stiff bare wire
- low-voltage supply
- switch
- leads
Get ready
⚠️ Safety first
- Use short pulses only — a shorted wire heats fast enough to burn.
- Low-voltage supply and an adult present.
Step 1 of 4 · Read
Think about what you just learned: say what "motor effect" and "Fleming's left-hand rule" mean in your own words before you start.
Step 2 of 4 · Do
Suspend a wire between the poles of a strong magnet and pass a brief current. Record which way it kicks, then reverse the current and reverse the magnet, tabulating the direction each time against the left-hand rule.
Step 3 of 4 · Observe
Record what actually happened, including anything that did not match what you expected.
Step 4 of 4 · Record
Write a conclusion that answers the question this lesson opened with, and state your uncertainty.
Question 1 of 2
Question 2 of 2
Mind = blown
🎢 You feel weightless on a roller coaster because you and the seat are falling at the same speed.
Nice work!
You got 0 of 2 right.
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✨ More to explore
🌍 Where you see this in real life: You use this every time you flip a light switch, ride a bike, or kick a ball.
🏆 Stretch challenge (try it this week): Time how long a small ball rolls down something, then change the slope and try again.
👨👩👧 For the dinner table: “Show me something at home that uses this kind of energy.”
Share this experiment
Send it to a parent who's looking for a 10-minute kitchen science win.
Ready?
The Motor Effect
Run the experiment. Find out what really happens.
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Print the whole Magnetism track
All 9th Grade Magnetism lessons as a printable PDF, with worksheets and answer keys.