The radioactive decay of 238U produces a particles with a kinetic energy of 4.17 MeV.
(a) At what speed do these a particles move?
(b) Put yourself in the place of Rutherford and Geiger. You know that a particles are positively charged (from the way they are deflected in a magnetic field). You want to measure the speed of the a particles using a velocity selector. If your magnet produces a magnetic field of 0.30 T, what strength electric field would allow the a particles to pass through undeflected?
(c) Now that you know the speed of the a particles, you measure the radius of their trajectory in the same magnetic field (without the electric field) to determine their charge-to-mass ratio. Using the charge and mass of the a particle, what would the radius be in a 0.30-T field?
(d) Why can you determine only the charge-to-mass ratio (q/m) by this experiment, but not the individual values of q and m?