Field due to a Straight Wire
The magnetic field of a straight wire is the first field pattern most students meet, and its circular shape is easy to state but harder to picture. This simulation plots the field lines around the wire and lets you probe the strength at any distance.
How to use this simulation
- Adjust the current and reverse its direction
- Move a probe to different distances from the wire
- Toggle between field lines and a field-strength map
What to look for
- Field lines are concentric circles with no beginning and no end
- Doubling the distance halves the field strength, not quarters it
- Reversing the current reverses the direction of every field line
The physics behind it
A long straight conductor produces circular field lines centred on the wire, with direction given by the right-hand grip rule. The magnitude follows B = μ₀I/(2πr), so the field is inversely proportional to distance — a slower falloff than the inverse-square laws you meet elsewhere.