Question

Assume electrons are accelerated through a potential difference of 20000 V inside a TV picture tube. What is the minimum wavelength that could be produced when the electrons strike the phosphor? (1 Å=10-10 m).

Answer 1

Is this Electricity and Magnetism or Modern Physics?

Answer 2

The electron will have energy=e*V where e is the charge on the electron and V=20000Volts. This is the maximum energy that the photon emitted could have and E=hv=hc/k where k is the wavelength.

Hence e*V=hc/k.
Solve for k.
The energy of the photon in terms of the wavelength of the wave is a concept of modern physics.