two views of an oscilloscope
In a high-voltage oscilloscope the source of electrons is a cathode at potential −125 kV with respect to the anode and the enclosed region beyond the anode aperture. Within this region there is a pair of parallel plates 5 cm long in the x direction (the direction of the electron beam) and 8 mm apart in the y direction. An electron leaves the cathode with negligible velocity, is accelerated toward the anode, and subsequently passes between the deflecting plates at a time when the potential of the lower plate is −120 V, that of the upper plate +120 V.
Fill in the blanks. Use rounded-off constants: electron rest energy = 5⋅105 eV, etc. When the electron arrives at the anode, its kinetic energy is _____ eV, its total energy has increased by a factor of _____, and its velocity is _____ c. Its momentum is _____ kg m/s in the x direction. Beyond the anode the electron passes between parallel metal plates. The field between the plates is _____ V/m; the force on the electron is _____ newtons upward. The electron spends _____ seconds between the plates and emerges, having acquired y momentum of magnitude py = _____ kg m/s. Its trajectory now slants upward at an angle θ = _____ radians.
A fast neutron that just happened to be moving along with the electron when it passed through the anode reported subsequent events as follows. "We were sitting there when this capacitor came flying at us at _____ m/s. It was _____ m long, so it surrounded us for _____ seconds. That didn't bother me, but the electric field of _____ V/m accelerated the electron so that, after the capacitor left us, the electron was moving away from me at _____ m/s, with a momentum of _____ kg m/s."