90. e/m

The ratio of e/m for an electron can be measured with an apparatus consisting of a spherical evacuated electron tube mounted inside of a Helmholtz coil setup. The electrons are projected to circle in the magnetic field, and you measure the radius of the circle, the current to the Helmholtz coils, and the accelerating voltage to determine e/m. (See also E/M and Helical Electrons.) This is experiment 2 in the 8E lab.