An electron enters a bubble chamber and produces a spiral track like that shown on the left in Figure Q20.13. The magnetic field is directed into the page, and the electron had an initial velocity of 2.7 3x10⁸ m/s.
(a) If the initial radius of the electron’s trajectory is 5.0 cm, what is its velocity when it has spiraled in to have a path with radius 2.0 cm?
(b) What is the corresponding change in kinetic energy? Give your answer in joules and electron-volts.
(c) Calculate the magnitude of the magnetic field present in the bubble chamber.
(d) What is the change in force on the electron in going from the initial radius to the final radius?

Figure 20.13

RIGHT- HAND RULE NUMBER 2 If q > 0, the force will be along +z. Right-hand rule number 2 gives the direction of the magnetic force on a moving charged particle. B.