PHYSICS & ELECTRONICS / MAGNETIC EFFECTS OF ELECTRIC CURRENT / PAGE 12 OF 50
Magnetic Effect of Current and Field Lines
The discovery that linked electricity and magnetism.
In 1820 Hans Christian Oersted saw a compass needle swing when placed near a wire carrying current. That showed that moving charge creates a magnetic field. Around a straight wire the field forms circles, and the right-hand grip rule gives its direction: thumb along the current, fingers curling the way the field points.
Original diagram: magnetic effect of current and field lines
Field lines leave the north pole of a magnet and enter the south pole. They never cross, and where they crowd together the field is stronger.
- A current always produces a magnetic field around it.
- Reversing the current reverses the field direction.
- Closer field lines mean a stronger field.
KEY IDEA
Straight wire: B = μ0 I / (2π r)Browse all 50 physics and electronics pages | Back to the course index