Magnetic field of bar, U-shaped, and electromagnet magnets
Integrated ScienceElectricity & MagnetismAges 12–13
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Electricity & Magnetism
Iron filings scattered on a card arrange themselves into a magnetic field pattern around the magnet; a compass needle placed in the field turns to follow the field lines. Students drag the magnet through the filings, tap an empty spot to place another compass, and press Flip poles to watch the needles swing around. For the electromagnet: drag the current slider, change the number of coil turns, switch off the current to make the field disappear, and reverse the current to swap the poles. A 3D mode lets students rotate the card with its iron filings, compasses and magnet to see the field lines loop through space from the North pole to the South pole.
Lesson: Magnets; Magnetic field; Electromagnets and their applications
What it shows
A magnet is surrounded by a magnetic field that acts on iron and other magnets. Iron filings line up along the field and reveal its pattern; outside the magnet, field lines run from the North pole to the South pole and crowd together where the field is strongest, near the poles. A compass needle turns to lie along the field lines. Between the poles of a U-shaped magnet the field is almost uniform. A current-carrying coil with an iron core acts as an electromagnet whose strength grows with the current and the number of turns, and whose poles swap when the current reverses.
How to use
Choose a Magnet type and drag the magnet across the filings, then tap empty spots to place compasses and compare their directions with the drawn field lines. Press Flip poles and watch every needle swing round. For the electromagnet, raise the Current (electromagnet) and the Number of coil turns (electromagnet) to see the pattern strengthen, set the current to 0, and press Reverse current. Switch to 3D and rotate the view to see the field lines loop through the space above the card.
Parameters you can change
- Magnet type Bar magnet, U-shaped magnet, Electromagnet (coil with iron core)
- Current (electromagnet) 0–5 A
- Number of coil turns (electromagnet) 100–1000 turns
- Draw field lines
- Iron filing density 12–36 columns
Questions to explore
- Where around a bar magnet do the iron filings gather most densely, and what does that tell you about the field?
- What is special about the field lines between the poles of a U-shaped magnet?
- When the current is 0 A, does the electromagnet still have a magnetic field, and how do the compasses show it?
