lesson
Updated 6 days ago · 3 views
Place a loose copper wire between two strong magnets and connect it to a battery. The instant you complete the circuit, the wire violently leaps into the air without anything touching it.
To understand why this push happens, we have to look at the two invisible fields colliding in that gap.
Two Separate Fields
In 1820, Danish physicist Hans Christian Ørsted discovered that electric current flowing through a conductor generates its own circular magnetic field around the wire.
Permanent magnets also create a magnetic field, with uniform straight field lines running from the north pole to the south pole.
📊A side-by-side 2D visual diagram on a light gray background (#f8f9fa). Card 1 (Left): 'Field Around a Wire' shows a cross-section circle of a wire with a current dot symbol, surrounded by concentric circular blue magnetic field lines with counter-clockwise arrows. Card 2 (Right): 'External Magnetic Field' shows a red North magnet pole on the left and a blue South magnet pole on the right, with straight horizontal green magnetic field lines flowing smoothly from N to S. Clean labels with modern typography (#1e2945).
What happens when you place that current-carrying wire directly inside the magnet's uniform field?
The Catapult Field
When the circular field of the wire overlaps with the straight external field, the two combine into a single distorted pattern called a catapult field.
On one side of the wire, both fields point in the same direction and reinforce each other to create a dense, strong field. On the other side, the fields point in opposite directions and cancel out, creating a weak field.
📊An interactive-style animated 2D cross-section diagram showing the 'Catapult Field' effect. Left has a red 'N' pole block, right has a blue 'S' pole block. In the center is a circular wire cross-section (with a central dot indicating current coming out of page). Above the wire, the field lines curve densely over the top (reinforcing). Below the wire, field lines are sparse and spread out (canceling). A prominent glowing downward arrow labeled 'Resultant Magnetic Force (F)' points from the dense upper region toward the weak lower region. A subtle pulse animation highlights the dense field lines pushing the wire down like stretched rubber bands.
Because magnetic field lines act like stretched rubber bands that repel each other, the crowded field lines push the wire toward the weaker region. This physical push is known as the motor effect.
In 1821, Michael Faraday used this exact field interaction to construct the world's first continuous electric motor.