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Sunday, May 3, 2009

Photoelectric effect and how it relates to the colour of stars

Photoelectric effect is the emission of electrons when light shines on a metallic surface. The emission of electron from this effect is called photoemission.

Materials such as metal will produce the photoelectric effect more readily. This is because the electrons in metals are free; they are only bonded lightly with its nucleus. That is the reasons why metals are good conductors (the electrons move when a voltage difference is placed across them) A collective movement of electrons is what we call “current”. Contrary to conventional thoughts, it is the movement of electrons or the negative charge that underlies the idea of what we consider “electricity” not +ve charge or protons.

When the photoelectric effect takes place, scientists can measure the electrons that are released by measuring the electrical voltage. They found out that it happens only with certain kinds of light. By doing further test, they discovered that what causes photoelectric effect is the frequency of light. The frequency of light also determines the colour of light that we see. Red colour is in the lower frequency and violet the highest frequency that our eyes can observe.


The higher the frequency, the more likely electrons will be emitted. The lower the frequency, the less likely photoelectric phenomenon will take place. It doesn’t matter how much power is used, you may use a thousand watts of low frequency light, but it would not cause the photoelectric effect to take place!

This has a really important implication, by discovering that energy is linked to light frequency. Increasing the intensity of light will produce more photons (or light) but it will not produce photoemission if the frequency is not high enough. The energy of the electrons emitted will also correspond to the energy or frequency of the light incident on the metallic surface: high frequency light will produce high energy electrons.

Conversely the energy of a system may be measure by the frequency of light it produces, a simple one is that produced by the Bunsen burner. The blue flame produced is actually hotter and energetic than the yellow flame. The same could be said for stars, the younger they are, the more energetic, as they age they will tend towards the lower frequency such as yellow and red.

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