by Glen Brizius

Created on: December 19, 2009

One of the most fascinating aspects of chemistry, and science in general, is the electromagnetic spectrum.  While the subject can become very complex, it can be elegantly summed up in a very simple equation that anyone can understand: Planck's Law.

This equation is as follows: E=hv.  E stands for energy.  h is a constant - Planck's constant, named after the discoverer of the scientific law.  v (the Greek symbol nu) stands for frequency - the number of waves passing past a given point in a given amount of time.

You see, light can be thought of moving in waves, like the waves in a pond when a pebble is dropped into the still surface.  The distance between the tops of the waves is called, understandably, the "wavelength".  For most visible light, this is a very small distance indeed - on the order of several hundred nanometers, where a nanometer is 10^-9 meters.  A very small distance.  More energetic waves such as X-rays or even gamma rays have a much shorter wave length.

Another way of writing the equation, an equivalent way, is the following: E = h(c/lambda), where c is the speed of light (a constant), and lambda is the wavelength.  For UV light, where the wavelength is quite short (and therefore the frequency is high), damage to the skin can occur as a result of the waves interacting with matter more intensely.  This is the reason that an overdose of X-rays can be harmful; too much exposure to these waves can result in genetic damage, as the waves are more energetic and can cause genetic damage to DNA strands.

On the opposite end of the scale we have radio waves, with wavelengths of several meters.  They can pass through solid objects without causing any damage at all, and can travel long distances, as they are not absorbed by matter very readily.

Light is a mysterious subject, but Planck's law breaks it down into an easily understood phenomenon.  Light with short wavelengths (and therefore, high frequencies) is more damaging than light with longer wavelengths (such as radio waves).  You can stand under a regular light bulb all day with no ill effects, but standing in the open sun on a hot summer day will quickly result in a nasty sunburn.  

It's simple, easily understood equations like these that help to make science so interesting and fun.  Anyone can understand the general principle, and with a calculator and a few reference values for the constants in the equation, anyone can readily calculate the energy given off by a given wavelength or frequency of light.  It's examples such as this that help to demystify the sometimes bewildering world of science.

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