We have seen the various ways moving charges and current can create magnetic fields. But what do magnetic fields do? How do charges react in a magnetic field?
It turns out that just as moving charges produce magnetic field, conversely magnetic fields exert a force on moving charges. The electric force was just q times E. Now we have velocity in the mix but the equation 29.18 is pretty simple still. Note how the cross-products returns again.
We can see directly in a Crookes' tube.
Look carefully at examples 29.10 and 29.11 particularly the latter. The radius of cyclotron motion is important. None of the cyclotrons equations are on the formula sheet because it is more important to be able to derive them then to just use them. Look at problem 64 from the end of chapter for a nice follow up on example 29.11.