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Electromagnets Worksheet
By the end you will: find what makes an electromagnet stronger and use the right-hand rule to find its poles.
A. Explore with the simulation
With the iron core in, try each setting and record how many clips are lifted.
Turns Current (A) Turns × current Clips lifted 100 1.0 200 1.0 100 2.0 200 3.0 Set 200 turns and 3 A, then take out the iron core. How many clips now? What does the core do?
Turn the current down to 0 A. Which way does the compass point now? Why?
Reverse the current. What happens to the poles and the compass?
B. Work it out
A coil of 50 turns carries 4 A. Another has 400 turns and carries 0.5 A. Which is stronger (same core)?
Inside a long coil, B = μ₀nI. Find B for 2,000 turns per metre carrying 1.5 A (μ₀ = 4π × 10⁻⁷ T·m/A).
C. Think it through
Give two reasons scrapyard cranes use electromagnets, not permanent magnets.
Answer key (for teachers and parents)
- 100 turns, 1 A: 4 clips · 200 turns, 1 A: 9 · 100 turns, 2 A: 9 · 200 turns, 3 A: 20 (the maximum). Same turns × current, same strength.
- None. The iron core makes the magnet about 100 times stronger; its own tiny magnets line up with the coil's field.
- North again: with no current there is no electromagnet, so only Earth's own magnetic field turns the needle.
- The north and south poles swap ends and the compass needle swings the other way.
- Equal: both are 200 ampere-turns.
- B = 4π × 10⁻⁷ × 2,000 × 1.5 ≈ 3.8 × 10⁻³ T (3.8 mT).
- They can be switched off to drop the load, and they can be made far stronger by using more current and turns.
Free to print and share for teaching. Made with the interactive simulation at jugnix.com/simulations/electromagnet.