Compass Above and Below Wire
Oersted's discovery began with a compass needle twitching near a current-carrying wire. This simulation places compasses above and below the wire, and the fact that they point in opposite directions reveals that the field wraps around the wire in circles.
How to use this simulation
- Reverse the current direction
- Move the compasses to different positions around the wire
- Change the current magnitude
What to look for
- Compasses above and below settle in opposite directions
- Reversing the current reverses every needle at once
- Deflection weakens with distance as the field falls off like 1/r
The physics behind it
A straight current produces a magnetic field in concentric circles around it, with direction given by the right-hand grip rule. Above the wire the field points one way; directly below, the same circular field line is heading the opposite way. Field strength follows B = μ₀I/(2πr), so compasses further from the wire deflect less.