## Overview This topic covers the properties of photons and the photoelectric effect. Learners study the electromagnetic spectrum and how to produce line emission and line absorption spectra from atoms. The wave-like behaviour of particles is studied using electron diffraction and de Broglie’s relationship is applied to both particles of matter and to photons. ## Working Scientifically The specified practical work in this topic gives learners the opportunity to use a wide range of experimental and practical instruments, equipment and techniques appropriate to the knowledge and understanding included in this topic; to use appropriate digital instruments, including electrical multimeters, to obtain a range of measurements; to correctly construct circuits from circuit diagrams using D.C. power supplies, cells, and a range of circuit components, including those where polarity is important. ## Mathematical Skills There are a number of opportunities for the development of mathematical skills in this unit. These include recognising and using expressions in decimal and standard form; using an appropriate number of significant figures; understanding simple probability; making order of magnitude calculations; translating information between graphical, numerical and algebraic forms; plotting two variables from experimental or other data; determining the slope and the intercept of a linear graph. ## How Science Works There are opportunities within this topic for learners to use theories, models and ideas to develop scientific explanations; to use knowledge and understanding to pose scientific questions, define scientific problems, present scientific arguments and scientific ideas; to carry out experimental and investigative activities, including appropriate risk management, in a range of contexts; to analyse and interpret data to provide evidence, recognise correlations and causal relationships; to know that scientific knowledge and understanding develops over time. Learners can research the difficulties encountered by trying to use the wave theory of light to explain the photoelectric effect and how the photon model of light was developed. Learners can also investigate how the Planck constant can be determined using light emitting diodes. ### Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the fact that light can be shown to consist of discrete packets (photons) of energy (b) how the photoelectric effect can be demonstrated (c) how a vacuum photocell can be used to measure the maximum kinetic energy, Ek max, of emitted electrons in eV and hence in J (d) the graph of Ek max against frequency of illuminating radiation (e) how a photon picture of light leads to Einstein's equation, Ek max = hf – , and how this equation correlates with the graph of Ek max against frequency (f) the fact that the visible spectrum runs approximately from 700 nm (red end) to 400 nm (violet end) and the orders of magnitude of the wavelengths of the other named regions of the electromagnetic spectrum (g) typical photon energies for these radiations (h) how to produce line emission and line absorption spectra from atoms (i) the appearance of such spectra as seen in a diffraction grating (j) simple atomic energy level diagrams, together with the photon hypothesis, line emission and line absorption spectra (k) how to determine ionisation energies from an energy level diagram (l) the demonstration of electron diffraction and that particles have a wave-like aspect (m) the use of the relationship h p  = for both particles of matter and photons (n) the calculation of radiation pressure on a surface absorbing or reflecting photons [[Specified Practical Work]] - Determination of h using LEDs