12.1b Matter waves

THE IB SAYS

Essential idea: The microscopic quantum world offers a range of phenomena, the interpretation and explanation of which require new ideas and concepts not found in the classical world.

Understandings: Matter waves

Applications and skills: Discussing experimental evidence for matter waves, including an experiment in which the wave nature of electrons is evident.

Guidance: -

International-mindedness: -

Utilization: The electron microscope and the tunnelling electron microscope rely on the findings from studies in quantum physics

Data Booklet: None

My vodcasts

De Broglie wave-equation

Working with the French army during WW1, the young graduate student Louis de Broglie reflected on Einstein's explanation of the photoelectric effect and his work on relativity. He thought that if light, traditionally thought of as a wave, can behave like a particle, maybe particles can behave like waves. Based on the equations of Plank and Einstein he derived an equation for the wavelength of matter. All particles and objects have a wavelength based on this equation, but it is only significant for very small particles.

The wavelength of accelerated electrons

By modifying the de Broglie wavelength equation with standard equations for kinetic energy and electrical fields, you can derive a relatively simple equation for the wavelength of an electron (or any charged particle) based on it's mass, charge and the accelerating potential difference. This expression is limited at very high energies due to relativistic effects, but they win't be encountered in IB DP Physics questions.

Davisson-Germer and Thomson

In the 1920's de Broglie's equation was tested using practical experiments by Davisson and Germer in the USA and, independently, by Thomson in Scotland. These both confirmed the wave like nature of electrons by diffraction them, and used the results of these experiments to investigate the nature of materials.

Additional videos

A solid approach at a good level

Resources from textbooks

Oxford Physics (2014): pages 480 - 482

Hamper HL (2014): pages 288 - 290

Relevant questions from Dot Point Physics (13 Quantum Physics and Nuclear Physics)

Pages 186 - 190

12.1a The photoelectric effect

12.1c The Bohr model