Jan 2017

Understanding Photoelectric Effect

January 27, 2017

The photoelectric effect is another of the fields within JC physics that it is critical to pay attention too. Here are the key points you will learn from our JC physics tuition and how to ace this field of physics.

What is the photoelectric effect?

The photoelectric effect is the closest you will come in your physics tuition to true quantum mechanics and wave-particle duality.
Incoming electromagnetic energy, when arriving at a surface, is split and light is absorbed and electrons emitted. Different materials are affected by the different threshold of frequencies.

  • Non-metals need extreme ultraviolet wavelengths
  • Near ultraviolet is sufficient for most metals
  • Visible light is all that is required for an alkali metal.


How does this tie with Quantum Physics?

Quantum physics is the brainchild of  Albert Einstein and he suggested the existence of photons of light, as a quantifiable light unit. He also gave us the Planck’s constant, which, when multiplied by the frequency of a light gives you the energy per quantum of light. Whether or not this means light must be particle is up for some debate, although it is generally accepted it does not. This also ties in strongly to the famous ‘special theory of relativity’ which was posited and developed by Einstein, often simplified to the famous
E = MC^2
With C being the speed of light in a vacuum and M being the particles resting mass. The actual version of this formula is slightly longer than this simplified one, and is used accordingly and depends on the application you are using it for.

These theories give us several important equations

Hv= W+E
Where h= Plank’s constant, v the frequency, W is the minimum energy to remove an electron from the surface of the metal, E the maximum kinetic energy of the removed electron

Things you need to know about photoelectric effect

  • For any metal, there is a frequency of radiation below which the effect will not occur. This is called threshold frequency.
  • The time between the light striking and the electron being emitted is a minute.
  • Once an electron is emitted, it’s maximum movement energy will depend on the frequency of the radiation that caused it, not the intensity
  • If the original radiation was linearly polarized to start with, emitted electrons will peak in the same polarization direction, indicating the direction of the electric field.

Where do we make use of this practically?

The photoelectric effect has several practical uses. Photoelectron spectroscopy, gold leaf electroscope, and most night vision devices use this effect. Surprisingly, it was also an intrinsic part of the tubes in the original cathode tube monitors and TVs.
As with so many principles learned in our physics tuition, the photoelectric effect is a simple one but has huge potential which is usefully harnessed in several technological fields to mankind’s development.

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