🧲 Magnetic Force on a Charge

📖 The Physics

A moving charge in a magnetic field feels a force F = qv × B with a strange twist: it is always perpendicular to the motion. A sideways force can't speed the particle up or slow it down — it can only change its direction.

So the charge is bent into a perfect circle. This is the principle behind mass spectrometers and cyclotrons.

Faster charges make bigger circles; a stronger field makes tighter ones. Flip the charge sign and it curves the other way (Fleming's left-hand rule).