What quantity did you change?
Labs / Physics
Magnetic Field Lines
Pick a source, then drag it around and slide the little compass through the field lines — the needle always snaps to the local field direction. The lines and iron filings are computed live from the magnetic dipole and Ampere's-law formulas, and the readout shows the field at the compass.
Labs / Physics / Magnetic Field Lines
Magnetic Field Lines
Pick a source, then drag it around and slide the little compass through the field lines — the needle always snaps to the local field direction. The lines and iron filings are computed live from the magnetic dipole and Ampere's-law formulas, and the readout shows the field at the compass.
Why it matters
Why explore this?
Physics explains how changes in forces, energy, motion, and matter produce results we can measure. This model lets you test one part of that relationship at a time.
Explore
Try the model
|B| 0 µTdir 0°
Investigate
Questions to test
Predict first, try it in the model, then use what you observe to answer.
What to try
- Park the compass in one spot, then flip the polarity. Which way does the needle jump, and why?
- Switch from the bar magnet to the straight wire. Why do the field lines turn into closed circles instead of arcs from N to S?
- Move the compass twice as far from the wire. Does the field strength halve, or fall off faster than that?
- Compare the current loop with the bar magnet up close. Do they look like the same kind of field from far away?
- Crank the current or strength to maximum. What changes about the field lines — their shape, or just the reading on the compass?
Explain
Make sense of what happened
Name the quantity you changed, the quantity that responded, and the physical rule connecting them. Use a readout or visible change as evidence.
Check
Before you leave
What measurable result changed?
Which physical idea connects them?
If you can answer all three using evidence from the model, you understand the main idea. If not, return to Explore and change one setting at a time.