Magnetic Fields in Physics

The magnetic force has one strange habit that explains most of this topic. It never does work, because it always acts at right angles to the motion, so it can steer a charged particle but it can never speed it up or slow it down. That is why a particle moving across a field goes round a circle at a constant speed, and why the time for one circuit does not depend on how fast it happens to be going. The blocks start from the force law, then follow the paths it produces and the devices that exploit them, such as the velocity selector and the mass spectrometer, before moving to the force on a current and the twisting effect that turns a coil into a motor.