Whenever you see a rainbow, whether it is one in the sky. or one where light passes through some glass at an angle, you see the result of dispersion.
In essence, dispersion is another application of refraction - as light enters a medium it bends.
Important to this phenomenon is that the amount of bending is not only affected by the incident angle and the difference in refractive indices, but also the wavelength of the light.
So in the case of white light, which is comprised of a range of wavelengths, longer wavelengths, such as the reds, bend less, whereas shorter ones, such as the blues and violets bend more.
The result is the wavelengths spread out, or disperse.
In essence, dispersion is another application of refraction - as light enters a medium it bends.
Important to this phenomenon is that the amount of bending is not only affected by the incident angle and the difference in refractive indices, but also the wavelength of the light.
So in the case of white light, which is comprised of a range of wavelengths, longer wavelengths, such as the reds, bend less, whereas shorter ones, such as the blues and violets bend more.
The result is the wavelengths spread out, or disperse.
So if all colour variations travel at the speed of light, why do some colours bend more than others?
Watch the video.
Let's quickly examine this before we look at the explanation why. In this interactive from pHET,
- Open up the second TAB: PRISMS
- Choose the glass triangular prism and choose the white light source (not monochromatic)
- Fire the light into the prism until you can see a rainbow
Try different prisms. Can you see why triangular prisms work best?