DIY - Pizza box model
Making an instrument to see spectral lines with a cardboard box and a CD.
You can make a nice spectroscope using pizza box and discarded or damaged CD. There is nothing special about the pizza box except that it is one-time-use-and-throw box (after its use no one wants it really) and that it is broad but not very thick. You can use any other box.
The pizza box that we used was 35 cm x 25cm and 2cm think. In fact you can make two spectroscopes using a box this big. We opened the box and folded it length wise and cut into half.
We now made a long box by folding the cut length equal to the side of the box as show by red arrows here. Running a nail along the line where you need to fold the side helps in folding.
There is hole cut in the box, presumably for moisture and heat to escape else the pizza would get soggy. We cut a slit on top of the box about a centimeter from the hole and a square window exactly opposite to this hole.
And pasted black sheet of papers out side the window of the box
We now cut the CD using scissors and further cut it along the red line as shown.
After that using a stiff plastic material the top portion of the CD is removed. This a delicate operation. Need to be done carefully and slowly so as not to damage the surface. This piece is then insert into the slit as shown below.
Our spectroscope is now ready. By making this makeshift arrangement as shown here we took pictures of spectrum of Compact Fluorescent light (CFL).
The bright spot to the right is the direct light from the bulb
And this is the zoomed spectrum.
One can now see beautiful spectrum peeping through the hole and looking a bit to the left or right. Even a reflected light will show you nice spectra.
The spectrum would look something like this
A few points to note:
It is not necessary that you should use pizza box. What is important is that that you should be able to see the slit clearly, with your glasses on if you use those. A normal person can see objects at a distance of 30 cm quite clearly with out straining his or her eyes.
Make the slit narrower and finer details you can see in the spectrum but at the cost of reduce intensity.
The CD we have used here acts like what is called diffraction grating. Learn more about these WWW has lot of good information about these. My favorite is HyperPhysics site of Georgia State University.
A diffraction grating would indeed give a better result. We used 12,700 Grooves/in from Edmund Scientific in a plastic 35mm slide mount. One can of course use a cardboard mount or make ones own) .
By narrowing the slit you can see what are called Fraunhofer lines. My favorite link on the web is Spacetech's Orrery.
Presently we have overcast skies of Monsoon. I have tried taking spectrum of the Sun and it has not been easy taking a picture using a digital camera - but here it is. One can see the Fraunhofer lines, though the lines look much more impressive when viewed directly.
... and here is the spectrum
of CFL in the lab
For those in
Send us a self addressed stamped envelope and we will send you a small piece (2cm x2cm) diffraction grating.
Please note: - This offer is to promote individual efforts by the students in making their own spectroscope. Therefore no bulk 'order' please - educational institutions may write to us separately.
Address your letter
Arvind Paranjpye / Samir Dhurde
Post Bag #4, Ganeshkhind, Pune 411 007
Please mention on top
A bit more with digcam and CD
Though it has been difficult to take the solar spectra using the pizza box spectroscope one can do wonderful thing using simple digital camera and a diffraction grating. Just hold the grating in front of the camera and shoot. Here are two examples of what we did a few months ago.
The one on the left is that of sodium vapor lamp in IUCAA campus. The right one is of full moon rising.