18 Quantum Physics

Pre-lecture activity

The video below is an introduction to some key ideas in Quantum Physics. You are required to do some simple internet/textbook searches to answer the next few questions.


  1. It is mentioned (video time of ~30s) that a light bulb has the same energy distribution as a gas. What is the energy distribution of a gas? How does this energy distribution look like? (You should include the links of some articles that you have read.)
  2. How does the energy distribution of a gas change with temperature?
  3. Please highlight what is difficult/confusing you found in the assignment. If there is none, tell me the interesting part about the assignment.

Some questions raised from the activity worth further elaborations

A light bulb produces photons of different energy? Why does the light bulb emit photons with different energy? Why not emit photons at the same energy?
  • Incandescent light bulb produces light through heating a metal to high temperature.
  • When the light is passed through a diffraction grating we see that the visible spectrum to be continuous, indicating that it consists of all visible wavelengths. Of course there is also a continuous invisible spectrum even though it is not shown below. 

  • Why does a heated substance emit continuous spectrum? It can be modelled by considering a "box" and how electromagnetic stationary waves can be set up in this box.

  • The 19th century physicists did consider each mode of vibration having the same energy but it always resulted in what is later known as the UV catastrophe.
  • This is only resolved in 1900 when Max Planck treated each vibration mode to have energy that is proportional to the frequency.

If light can pass through glass pane, does photon even have a physical form?
  • Why is glass transparent?

  • Classical mechanics that we learn up to high school is on the dynamics of point particles where the particles do not have any physical dimension. The particle model in the form of a ball is for illustration purpose and has become our mental model of what a particle should look like. 
  • The particle of light does not have any physical form as far as scientist can tell. Once again the ball model confused many learners and lead to many unnecessary misconceptions.

How do light particles knock off electrons and other particles? is light a matter if it is made up of particles that have mass?

How light can actually be similar to gas and how light could actually be made of particles that behave like gas particles?
The difficult part is the lack of understanding of why light bulb would have the same energy distribution as a gas.
Does the light behave exactly the same way as the gas?
How can the atoms inside the light bulbs relate to the atoms outside and cause the light to spread out?
Why quantum physics has something to do with energy? Can I consider quanta as the quantification of energy which is invisible?
Confusing: What is the difference between energy and energy distribution?
wave particle duality
The controversy of wave-particle duality of light - what exactly do we need to know about this?
seems very chemistry-y.
It was difficult interpreting the equations I found in my research (i.e Schrodinger's equation etc)
What is the difference between quantum physics and the Newtonian physics that we learnt for the past few years? 

Lecture Slides

Introduction (download)

Photoelectric Effect (download)

Bohr Atom (download)

Line Spectral (download)

X-ray (download)

Wave-Particle Duality (download)


Wave Function (download)

Quantum Tunnelling (download)

Uncertainty Principles (download)

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