Should I Pursue a Double Slit Experiment for My Physics EEI?

[AXidenT]

(Hope this is the right forum)

For my Physics EEI (year 12 extended experimental investigation) I'd really like do some sort of variation of the double slit experiment that can deviate into wave like behaviour of matter etc... I've found ways to have the interference patterns shown using a laser pointer and film, but problem is there isn't enough variation to collect significant amounts of data to base the EEI on.

I was thinking I could use different frequencies of light/laser/whatever medium is being used and using them at different distances and measuring maybe a different in the interference patterns or something, but I'm not sure what that would show if anything.

Is it worth pursuing this, or should I focus on another experiment instead?

Thanks, sorry if I didn't give enough information.

 

[Delphi51]

It would certainly be exciting to do the double slit for light and for particles (electrons?). Alas, the light is probably too easy and the electrons too hard. Unless you can find a university lab that would let you use some of their equipment and advice. It is possible for an amateur to make a vacuum tube (if you can borrow a vacuum pump and figure some way to seal it - probably glass melting). Can you make slits sufficiently close together (better calculate that before starting!)? Maybe use a disassembled webcam as the sensor.

 

[AXidenT]

Well talked to some teachers at school today and for the electrons we may be able to use a university's equipment for that one, so it is actually a possibility!

My concern though is whether we would be able to collect enough data to "systematically anaylse" (one of the criteria). I can't think of any variables that we could change that would produce meaningful data. Any ideas? :S

 

[Delphi51]

I don't think you will get much data on the electron experiment - one pattern would be a triumph! But it should be fairly routine to get lots of data for light. The formula x = nLλ/d could be varied every which way. For example, use slits with different d values (order some gratings NOW if your school doesn't have a few different ones) and measure the x distances. With some persistence, you should be able to make measurements with ordinary light (chemistry will have some gas discharge tubes with known wavelengths - hydrogen lines, etc) rather than lasers, so you can vary λ. Put those two data sets together and you can experimentally deduce the formula with the usual graphing techniques.

There is a little controversy with the L in that formula. Many high school textbooks take L to be the perpendicular distance from the slits to the screen but in fact it is the hypotenuse in the nλ = d*sin(θ) formula. It only makes a significant difference when θ is large but no problem getting large angles with the laser. Comparing the data points and the formulas with L used both ways should be good for a graph or two.

You may think of some "slits" to measure with interference patterns. Fine screens, cloth, and plant tissues come to mind. You see interference patterns in everyday life, for example from the sun shining on screen doors. Are these really from interference when the mesh is thousands of times wider than diffraction gratings? Some close observations and calculations would be most interesting. If you do anything with that, I would really appreciate a PM with the details.

Another dimension to the whole thing is the intensities of the bright constructive interference lines with different n values. You could have a go at measuring these with photocells or photoresistors and some very simple electronics. I have no idea what pattern or formula you might find. I have seen some delightfully complicated intensity functions of angle for refraction.