22.9 Exercise 1

An experimentalist fires a beam of electrons, creating a visible path in the air that can be measured. The beam is fired along a direction parallel to a current-carrying wire, and the electrons travel in a circular path in response to the wire’s magnetic field. Assuming the mass and charge of the electrons is known, what quantities would you need to measure in order to deduce the current in the wire?

1. the radius of the circular path
2. the average distance between the electrons and the wire
3. the velocity of the electrons
4. two of the above
5. all of the above