This unit develops fundamental ideas about the nature of matter, touching on key ideas in particle and nuclear physics. It is also concerned with a variety of models and should be used both to discuss the nature of models in physics and their limitations. Learners will be familiar with a particle model for the electron and atom and a wave model for light. The photoelectric effect and electron diffraction experiments show that these models, whilst useful, are limited and incomplete descriptions of reality. This leads to the ideas of ‘wave-particle duality’ whose interpretation has challenged physicists and philosophers for over a century.

 

The discrete arrival of gamma-ray photons in a Geiger counter or of photons/electrons in a low intensity experiment provide evidence that EM waves transfer their energy to matter in discrete quanta. The experimental properties of the photoelectric effect cannot be explained by a purely wave-like model of light but can be explained by the deceptively simple photon model proposed by Einstein. Learners need to master this explanation but should then be drawn back to the central dilemma – we now have two models for light, neither of which captures all of light’s properties. Experiments with the electron diffraction tube can be used to show that matter also exhibits wave-particle duality. Learners need to become confident with the de Broglie relations and their interpretation.

 

Lesson objectives(12th Grade NIS Program):

12.2.2.1 – give evidence of the particulate nature of electromagnetic radiation;
12.2.2.2 – recall and use E=h f;
12.2.2.3 – show an understanding that photoelectric effect provides evidence for the particulate nature of electromagnetic radiation;
12.2.2.4 – show an understanding that interference and diffraction provide evidence for the wave nature of electromagnetic radiation;
12.2.2.5 – know the definition of photoelectric threshold frequency;
12.2.2.6 – explain the photoelectric phenomenon in terms of photon energy and work function energy;
12.2.2.7 – explain why work function is independent of light intensity, whereas photoelectric current is proportional to intensity;
12.2.2.8 – Know and apply the formula when solving problems, and understand as an expression resulting from the Law of conservation of energy;
12.8.2.9 – describe and interpret qualitatively the evidence provided by electron diffraction for the wave nature of particles;
12.2.2.10 – know and use the relation for the de Broglie wavelength: λ = h/P;
12.2.2.11 – show an understanding of the existence of discrete electron energy levels in isolated atoms (e.g. atomic hydrogen) and deduce how this leads to spectral lines through energy levels;
12.2.2.12 – distinguish between emission and absorption line spectra;
12.2.2.13 – recall and solve problems using the relation h f = E1 – E2;
12.2.2.14 – understand and explain the stability conditions of existence of the atom using Bohr’s postulates;
define the terms such as valence band, conduction band and band gap;

The Resources for this course had taken from different sources in Web

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Admin bar avatar Zhakupov Nursultan

Physics teacher in Nazarbayev Intellectual school, Pavlodar.

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