Physics

Make your own spectroscope

April 13th, 2009

I thought I’d try and make my own spectroscope. A spectroscope allows you to split up light from a source into its separate wavelengths. Scientists use this instrument to find out what chemical processes are taking place inside distant stars – every element has its own “signature” and from the spectrum of light given out by a reaction (the emission spectrum), you can tell which elements are involved. A quick search on the web found some ideas, and this is how I made my own spectroscope.

I started with a cardboard tube, razor blades, scissors and scalpel and some duct tape. Are you thinking of trying this yourself? I need not warn you to be careful with sharp things. They cut, you bleed and then you die. Be careful. Really, get help if you are little or unsteady with your hands. Better still, don’t do it at all unless you’re prepared for any consequences.

Anyway. The cardboard tube was used to send me some posters for my classroom, but I guess any tube will do. It doesn’t have to be as big as this one. We need a diffraction grating for the eyepiece end of our spectroscope. CD’s and DVD’s have fine lines in them which are perfect for this but they usually have one side painted – the inside is mirrored to make the CD player able to read the data on the CD. We need to remove this paint and the mirror surface. Start by scratching a little of the paint away from near the edge. Then use small strips of the duct tape to lift the paint off the CD or DVD. You can use clear sellotape for this, but the glue on the duct tape is stronger and makes it much easier. Work all the way around the CD until it’s clean and you should be able to see the rainbow effect from the lines in the surface by holding it towards a light. Later, you are going to cut the CD with scissors. It might be a good idea to warm it up – on a radiator or by placing it in hot water for a while to make it easy to cut without shattering or slipping.

Next, we need to make the objective end – for this, we need a fine slit: this can be achieved by cutting into any material but I am going to be using two edges of a razor blade and fix them a short distance apart. My tube came with little plastic inserts each end to keep the posters safe. With my scalpel, I cut an opening in one of them and fixed the razor blades carefully with duct tape. Remember to put something underneath whilst you are cutting with the scalpel, so you don’t damage your lovely kitchen surfaces.

Before fitting the slit into the tube, I painted it black (actually, I used a permanent marker pen) to reduce the light coming through the end of the tube except through the slit itself. I made sure that any sharp edges were well covered with duct tape and that it all fitted securely inside the end of the tube.

Now, I cut a circle from the CD to fit securely into the other end of the tube to provide the diffraction grating for the eyepiece. The grating has to fit such that the lines on the CD go in roughly the same direction as the slit at the objective (far away) end of the spectroscope. You might need to try it – point the end with the slit towards a household lamp and rotate the eyepiece until you get the best effect. Then, tape it securely in place and – bingo! – your very own spectroscope is complete and ready for action.

One more word of warning, please don’t point a spectroscope or anything else in such a way that you look directly at the sun. Your eyes may be permanently damaged as a result. Just be careful, but enjoy a little practical physics. I’ll leave you with two results – one, a spectrum I obtained by pointing the spectroscope at my kitchen lamp – it’s one of those new low-energy lamps and clearly shows the emission spectrum from the phosphor coating. The second image is a continuous spectrum obtained from our own star.

Categories: Practical Physics | Tags: spectroscope