A Force That Only Turns

You'll learnwhen a magnetic force exists at all, which way it points, why an electron bends the opposite way to a proton, why the speed never changes, and why the faster particle traces the wider circle.

Put a proton in a strong magnetic field and let go: nothing happens. Fire it along the field lines: still nothing. Turn it across the field and a force appears at once — one that can bend the path into a circle but can never change the speed. Twelve short steps; press Next for each one.

12 STEPS · 6 QUICK CHECKS · MOTION ACROSS B · SQUARE TO BOTH · NO WORK, EVER · v2

no motion across B, no force · square to both · no work, so no change of speed

Before you start

What you're looking at

A proton in a strong, uniform magnetic field, drawn first as lines in the page and later as crosses pointing into it.

The question

When does the field push on the proton at all — and what does that push actually do to its path?

Step 1 / 12