Coils Entering and Exiting a Magnetic Field
The shape of a coil changes the whole character of its induced EMF as it crosses a field boundary. This simulation runs triangles, circles, squares and rectangles through the same field and plots their EMF traces for comparison.
How to use this simulation
- Select the coil shape
- Set the entry speed and field strength
- Run the coil fully through, entering and exiting
What to look for
- A rectangle entering squarely gives a constant EMF; a circle gives a curved pulse
- EMF drops to zero once the coil is entirely inside the field, where flux stops changing
- Exiting produces an EMF of opposite sign to entering
The physics behind it
Induced EMF depends on the rate of change of flux, ε = −dΦ/dt, and for a coil entering a field at constant speed that rate depends on how quickly the enclosed area inside the field grows. A rectangle entering edge-on gains area at a constant rate and produces a flat EMF; a circle or triangle gains area at a varying rate, so its EMF changes shape as it crosses.