Spectrometers are used, like prisms, to spread light out into its component colours. They can reveal the composition of stars or streetlights.
Cut a 1cm square in the middle of one piece of card. Snap the CD -- take a bit that covers the hole. Peel away any label so that it's transparent. Use tape to stick it over the hole.
Use the knife to cut a 2cm by 2mm slit in the middle of the other piece of card. Tape the two razor blades either side of the slit so they make it just less than 1mm wide.
Tape the windowed card to one end of the tube, and the slit (make sure the blades are securely attached) to the other: you've just made a spectrometer.
When you look through the window, you should see only light from the slit. Point the spectrometer towards daylight. You should see a small, smooth rainbow somewhere in the tube.
Light entering the tube spreads out -- waves do this when passing through slits; it's diffraction. The CD makes the spectrum visible. You see a full spectrum from daylight.
Compare daylight to the spectra you get from a light bulb or LED -- or sodium (orange) street lights. Try also looking at neon signs or TV or computer screens.
This article was originally published by WIRED UK
