PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation
Problem
Photon energy varies inversely with wavelength, a fact that has consequences across the electromagnetic spectrum.
(i) Starting with fundamental constants, derive an expression for the energy E (in electron-volts) of a single photon in terms of its wavelength λ (in nanometres).
(ii) Using your expression, calculate the energy difference between individual photons of red light (λ=700nm) and violet light (λ=400nm).
(iii) The ionisation energy of the hydrogen atom is 13.6eV. Determine the minimum frequency of electromagnetic radiation capable of ionising a ground-state hydrogen atom.
(iv) Identify the region of the spectrum corresponding to the frequency obtained in part (iii) and state one reason why astronomers study this radiation when observing interstellar hydrogen clouds.