Question

What kind of relationship is there between wavelength and frequency? As frequency increases, what happens to the energy gap associated with it?

Answer 1

If you draw a beam of light in the form of a wave (without worrying too much about what exactly is causing the wave!), the distance between two crests is called the wavelength of the light. (It could equally well be the distance between two troughs or any other two identical positions on the wave.) You have to picture these wave crests as moving from left to right. If you counted the number of crests passing a particular point per second, you have the frequency of the light. It is measured in what used to be called "cycles per second", but is now called Hertz, Hz. Cycles per second and Hertz meanexactly the same thing. Orange light, for example, has a frequency of about 5 x 1014 Hz (often quoted as 5 x 108 MHz - megahertz). That means that 5 x 1014 wave peaks pass a given point every second. Light has a constant speed through a given substance. For example, it always travels at a speed of approximately 3 x 108metres per second in a vacuum. This is actually the speed that all electromagnetic radiation travels - not just visible light. There is a simple relationship between the wavelength and frequency of a particular colour of light and the speed of light: . . . and you can rearrange this to work out the wavelength from a given frequency and vice versa: These relationships mean that if you increase the frequency, you must decrease the wavelength. Compare this diagram with the similar one above. . . . and, of course, the opposite is true. If the wavelength is longer, the frequency is lower. It is really important that you feel comfortable with the relationship between frequency and wavelength. If you are given two figures for the wavelengths of two different colours of light, you need to have an immediate feel for which one has the higher frequency. For example, if you were told that a particular colour of red light had a wavelength of 650 nm, and a green had a wavelength of 540 nm, it is important for you to know which has the higher frequency. (It's the green - a shorter wavelength means a higher frequency. Don't go on until that feels right!)

Note: nm = nanometre = 10-9 metre.