NARRATOR: When a beam of light hits a piece of glass straight on, it passes right through it.
Shot of beam of light hitting glass.
NARRATOR: But the waves that make up the light actually get slowed down by the glass, and only go back to their normal speed when they come out the other side. That slowing down is what causes white light to split into a rainbow of colour whenever it hits glass on an angle.
Shot of light hitting glass prism and splitting into rainbow spectrum.
NARRATOR: It happens because glass slows some colours of light more than others and because slowing down on an angle makes light bend. It's easy to understand the bending if you picture how the light waves would look from above, like how waves at the beach look if you see them from the air.
Shot of lines of various colours.
NARRATOR: And while white light's made up of all the different colours of light, it also helps to look at them one colour at a time. When a wavefront of red light hits glass on an angle, the part of the wave that enters the glass first gets slowed down before the rest, and that changes the angle of the whole wave, like how waves bend around a cliff. Violet light get slowed down even more by glass so its waves bend more.
Shot of red light and violet light bending at different angles.
NARRATOR: All the other colours get bent somewhere in between.
Shot of various colours of light bending at different angles.
NARRATOR: So the colours get separated when they first enter the glass on an angle, and they spread out even more when they speed up on an angle as they leave. The reason the different colours slow down different amounts in glass is because they've got different wavelengths. Red light has the longest wavelength, followed by orange, yellow, green, blue, indigo, and, finally, violet, with the shortest wavelength. And the shorter the wavelength, the longer it takes to travel through glass. That's because light interacts with electrons in the molecules that make up glass. Long-wavelength light, like red, only interacts a bit with the electrons, so it doesn't get slowed much. But shorter-wavelength — violet — light interacts more so it gets slowed down more.
Shot of violet light moving slowly through electrons.
NARRATOR: So it's the combination of hitting glass on an angle and different wavelengths interacting with the electrons in the glass different amounts, that makes light hitting a prism spread out into a beautiful spectrum of colour, and some classic album cover art.
Shot of light splitting into rainbow spectrum, resembling Pink Floyd's The Dark Side Of The Moon.
