Are you a student of Physics 30? Are you as frenzied by quantum mechanics as I am? Well, fear not, your savior is here with a quick run through on many of the concepts covered in Quantum Physics.
I therefore welcome you to… Quantum Physics Part 1: The Beginning
- As you may know, light was quantized, ie, restricted to a number of possible values. Basically, light is a bundle of ‘packets’ of energy called ‘photons’, and each photon can carry only a certain amount of energy.
- Blackbody- An object that completely absorbs any light energy that falls on it, from any part of the EMR spectrum. After heating up, it becomes a perfect radiator.
- Blackbody radiation curve shows that the shortest wavelength has the highest amount of energy. Thus, shorter wavelengths are more efficient in emitting larger amounts of energy.
Blackbody radiation curve. As you can see, shorter frequencies of light(ie, blue) have the highest amounts of energy) - This lead to a disturbing conclusion- if an object was heated enough, it would emit EMR of short wavelengths like UV light, X-rays, etc.
- However, this did not happen (phew!). This error was called the “Ultraviolet Catastrophe” as according to classical Physics, the increase in frequency(or decrease in wavelength) of EMR absorbed by the blackbody should have resulted in it radiating EMR of higher frequencies and shorter wavelength.
- Max Planck, the genius that he is, quantized energy- he proposed that light carried energy in discrete bundles and each bundle could have only a limited amount of energy. And ladies and gentlemen, we have come to Planck’s formula-
E = nhf
where E is the energy of the quanta/packets of energy(J) , n is the number of quanta, h is Planck’s Constant(which may vary, I use 6.63×10^-34 J/s) and f is the frequency of light.
(The frequency of light can be calculated using f = c/λ ) - Einstein added to this idea of ‘quanta’, proposing that light could be quantized. Boom, you got the photon!
Max Planck 
Albert Einstein - Because of this theory, we could relate the emission of photons from its source. Which basically means, you cannot expect a human to radiate Gamma rays. Because that would be silly. And dangerous.
- Photoelectric Effect- The emission of electrons from a metal plate when EMR of high frequency(UV and higher) is shone on it.
The Photoelectric Effect - An electron on the metal plate absorbs the energy of the photon and escapes.
- Work Function(φ/W)- The minimum amount of energy a photon must possess in order to cause photo-emission, ie, emission of electrons.
- Threshold Frequency- The minimum frequency the photon must have in order to cause photoemission.
- Stopping potential- The potential difference for which the kinetic energy of the photoelectron is equal to the work done in moving it against it(the potential difference).
Vstop = E/q ,where E is the maximum kinetic energy of the photoelectron and q is the charge of the electron.
(* A photoelectron has the same mass and charge as an electron.)
This is the conclusion of Quantum Mechanics Part 1! In Part 2, I will talk about Compton’s Effect, Heisenberg, Schrödinger, De Broglie, and all the interesting concepts they came up with. Ciao till then!
For more information, check out these videos-
This, this, and this.
