Grade 7 · Science · Unit 4 of 6
Magnets & Motors
Electromagnets, motors and generators
What your child practises
Magnetic poles and fields, building stronger electromagnets (with a data table to extend), and how motors and generators change energy from one form to another.
NWT Curriculum learning standard: Electromagnetic force: magnetism, field lines, electromagnets, motors and generators
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A generator changes…
- heat into magnetism
- motion into electrical energy
- electrical energy into motion
- light into sound
motion into electrical energy
Hint: Spinning a coil near a magnet (or a magnet near a coil) produces an electric current.
Question 2
Motor or generator? Sort each device.
Sort into: ⚙️ motor (electricity → motion) · ⚡ generator (motion → electricity)
- 🔦hand-crank flashlight
- 🔄ceiling fan
- 🏭steam turbine in a power station
- 🪥electric toothbrush
- 🧺washing machine drum
- 🌬️wind turbine
- 🔧electric drill
- 🚲bike wheel light dynamo
⚙️ motor (electricity → motion): ceiling fan, electric toothbrush, washing machine drum, electric drill · ⚡ generator (motion → electricity): hand-crank flashlight, steam turbine in a power station, wind turbine, bike wheel light dynamo
Hint: A motor turns electrical energy into motion. A generator turns motion into electrical energy.
Question 3
Which metal is strongly attracted to a magnet?
🧲- copper
- gold
- aluminum
- iron
iron
Hint: Iron, nickel and cobalt (and steel, which is mostly iron) are magnetic. Most other metals are not.
Question 4
Outside a bar magnet, which way do magnetic field lines point?
- from the south pole to the north pole
- straight up away from both poles
- in circles around the middle only
- from the north pole to the south pole
from the north pole to the south pole
Hint: By convention, field lines leave the north pole and curve around to enter the south pole.
Question 5
Why do scrapyards use electromagnets, not permanent magnets, to lift old cars?
🏗️- An electromagnet can be switched off to drop the load
- Permanent magnets can't lift metal
- Permanent magnets only attract plastic
- Electromagnets work without electricity
An electromagnet can be switched off to drop the load
Hint: Turning the current off makes the electromagnet let go exactly where the crane operator wants.
Question 6
Students tested an electromagnet with different numbers of coils. If the pattern continues, how many paper clips would 40 coils pick up?
Electromagnet test: wire coiled around an iron nail Coils of wire Paper clips picked up 10 5 20 10 30 15 answer box
20
Hint: Every 10 coils picks up 5 clips. 40 coils is 4 groups of 10, so multiply 4 × 5.