Physics Tutorial 19.1 - Thermal Radiation. Photon as the Quantum of Light

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There are 6 lessons in this physics tutorial covering Thermal Radiation. Photon as the Quantum of Light. The tutorial starts with an introduction to Thermal Radiation. Photon as the Quantum of Light and is then followed with a list of the separate lessons, the tutorial is designed to be read in order but you can skip to a specific lesson or return to recover a specific physics lesson as required to build your physics knowledge of Thermal Radiation. Photon as the Quantum of Light. you can access all the lessons from this tutorial below.

In this Physics tutorial, you will learn:

What is thermal radiation? What object(s) produce(s) it?
What is total emissivity?
What is spectral emissivity and how does it differ from total emissivity?
What are the factors affecting emissivity of objects?
What is a black body? How does it radiate EM waves?
How do reflection and absorption abilities of an object relate to each other?
What can we find using the Stefan-Boltzmann Law and Wien Law?
What are the drawbacks of classical approach in thermal physics?
What issues were present when comparing the theoretical and experimental graphs?
Why the findings of Max Planck were so important in modern physics?
What is the nature of light (continuous or discrete)?
How can we find the energy of radiation?

Introduction

In classical physics, light was considered as a (transverse) wave, as explained in Section 12 of this course. This is because light possesses all physical properties of waves such as reflection, refraction, interference, diffraction and polarization. However, this approach did not give satisfactory answers to a number of light-related phenomena observed in experiments. For example, if light is considered as a wave, we cannot use the formula

E = m ∙ A² ∙ ω²/2

explained in tutorial 11.3 as light waves (unlike mechanical waves) have no mass of medium involved, as they mostly propagate in vacuum.

Likewise, if light is considered as a pure wave, we cannot use the relativistic equation

ε² - p² ∙ c² = m²₀ ∙ c⁴

explained in tutorial 18.6 either, as a pure wave has no rest mass m₀.

Therefore, it is obvious that a completely new approach must be used to explain any light-related phenomena, as light is different from all the other physical quantities discussed so far. This need for such a new approach gave birth to a new theory - the corpuscular (particle) theory of light, which we will explain gradually, starting from this tutorial.

Please select a specific "Thermal Radiation. Photon as the Quantum of Light" lesson from the table below, review the video tutorial, print the revision notes or use the practice question to improve your knowledge of this physics topic.

Modern Physics Learning Material
Tutorial ID	Physics Tutorial Title	Revision Notes	Revision Questions
19.1	Thermal Radiation. Photon as the Quantum of Light
Lesson ID	Physics Lesson Title	Lesson	Video Lesson
19.1.1	What is Thermal Radiation?
19.1.2	Total and Spectral Emissivity
19.1.3	Radiation of a Black Body
19.1.4	Stefan-Boltzmann Law
19.1.5	Wien's Law
19.1.6	The Ultraviolet Catastrophe and Planck's Hypothesis

Whats next?

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Continuing learning modern physics - read our next physics tutorial: The Photoelectric Effect

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