Friday, May 15, 2015

Making the Pizza Box Spectroscope


All the pieces needed for the pizza box spectroscope.
The pizza box spectroscope is a fun project to add to your atomic model unit.  Students can make an accurate tool to measure the wavelength of light using a pizza box, a diffraction grating, two razor blades, a plastic rod, and some metal tape.  The project is fun, easy to complete, and produces excellent lab data.  The wavelength measurements are typically within 1% of the accepted value using a calibrated pizza box!  
Chemistry teachers making spectroscopes at ChemEd'13 in Waterloo.
I learned how to do this project at ChemEd'13 at Waterloo University from Edmund Escuadero's session titled "Make and take:  Construct an inexpensive calibrated spectroscope."  Every participant made their own pizza box spectroscope in the workshop and learned how to calibrate it using a mercury lamp.  The process was so fun and relatively simple; a perfect idea to bring back to my school to do with my Honors Chemistry students.  The first year I used it in a collaborative project with the astronomy classes, and this year I did it just with my chemistry students as part of the atomic model unit.  

The original experiment instructions can be found in the PSU Chemtrek Lab Manual  (ISBN:  978-0-7380-2849-1) .  In the lab manual you will find detailed instructions for constructing the pizza box spectroscopes, calibrating the instrument, and some experiments you can do with them.

In my class, I used my double block (80 minutes) to construct and calibrate the boxes.  This was sufficient time for most of my student groups to finish this part of the project.  On the second and third days ( both 45 minutes-long classes)  students used the spectroscope to measure the lines in the hydrogen spectrum, and then they identified several unknown elements and a mixture of two elements.  I even gave a lab practical question on the unit test in which they had to measure two lines on a spectrum.  They were graded on the accuracy of their measurements because I knew how good their boxes were working from their lab data.
These students are tracing my template onto their pizza box.
I decided not to give out any written instructions for constructing the spectroscopes.  To get them started, I made a pizza box template which student groups copied onto their own boxes.  I put out my spectroscope as a model (yes, I'm that proud of it!) so they could see how it's supposed to look when constructed.  Once the template was traced onto their own box, the lab groups used a box cutter to cut out holes for the diffraction grating and the light slit.  The funny part about the whole project was watching kids figure out how to fold a pizza box.  It's not as easy as the pizza guys make it look!
Once the template is drawn, students use box cutters to cut out the eye hole and slit hole.

These students are taking photos of the whole process for their lab report.
Once the box was constructed, the students fastened their diffraction grating to the front and two razor blades (to make a narrow slit of light entering the box) at the back.  They fed the pre-marked plastic rod into the holes and then closed up the whole thing with metal tape.  The metal tape was important because it helps to minimize the light "noise" coming into the spectroscope.  The tape also gives the boxes a modern, sci-fi-ish look that all found very aesthetically pleasing.  We figured out that inserting the rod BEFORE closing up the box was critical because the rods are very difficult to feed through the holes of the box when it's closed up.

The metal tape is important to seal off gaps to avoid stray light from entering the box.
I didn't think much about the size of the pizza boxes, but it tuns out that the ones I got from our local pizza place were slightly larger than last year.  (Thank you Pizza 101 for donating the pizza boxes for the project!)  This only became I problem when I realized that my plastic rods were too short!  The end of the rod disappeared into the box when we tried to measure the red light.  I quickly figured out that 1.5 feet of plastic rod for each group was not going to be enough for all three classes.  As fate would have it, our head of school called a "head master holiday" on the second day of the project.  This meant that one of my classes missed the double block, and thus did not get to make their own pizza box spectroscopes.  I was saved!  These kids learned how to use the boxes from last year (so I glad I saved a few) and still got the full experience of calibrating and measuring with a pizza box.  I'll order more plastic rod for next year.
It's hard to limit the light "noise" from the holes for the plastic rod.
The diffractions gratings that Edmund recommended for this project are from a company called spectralworkbench.org.  Although they were slightly more expensive than others, Edmund emphasized the importance of this part of the box and how much he liked these particular diffraction gratings.  Although there is an initial cost to purchase the diffraction gratings, I can use them every year to make new boxes.   I decided to throw out the old razor blades when I deconstructed the old boxes because they rusted over the summer and it seemed like a bigger hazard to get a cut by a rusty razor blade.
Putting the finishing touches on the box to minimize stray light and make it look cool.
The spectroscopes were ready for calibration by the end of the double block.  I have written a separate post about calibrating and using the spectroscopes.  

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