I don't see any way to avoid some bold assertions. Repeat experiment with LEDs to contradict wave picture predictions.
Perhaps: show heating metal by electricity to get light (light bulb) point out reverse is possible: discharge electroscope. Should be good enough for a science fair.
The black box effect can be mitigated by also showing the discharging electroscope. The trick is to set up the wave theory predictions to disprove. The slam-dunk would be to show the absorbtion spectrum for the LED. In a wave delivery - the red light should eventually produce a current - when it has delivered enough energy. The downside is that and LED is sort of a "magic box" that might not convince some people. Including multimeter, the set up costs about $20-$40. When you shine a blue LED on a red LED you get a current, but not the other way around. A blue LED needs a higher energy photon to create a current than a red LED. If you use LEDs they can be used to absorb light. Then again - at your level - maybe just showing the phenomenon and asserting the quantum description will be good enough for the science fair judges? If resources are good, then, there is always setting up an oven and spectrometer for blackbody radiation, Millikan's experiment, and a host of others. Maybe you have the money to buy the equipment? You need to be able to show that "light delivers energy in lumps" is the easy way to model this.īut you never know - maybe your school has the equipment? You can just charge an electrometer and discharge it by shining light on it - but that's not the quantum part. Trying to get the same effect from a wave model is tricky. Add 2-3 drops of yellow food coloring and mix well. Heat approximately 1 cup of water to steaming or just boiling. Add 2-3 drops of blue food coloring and mix well. The photo-electric effect should be good if you can set it up. Add approximately four cups of water to a container. Youngs interference has a wave-model for it, the cern one is cool - but the light pulse was very short and sharp, so a wave could have delivered the energy to make the plate ring (the ring would probably be different - but how would you show that in the experiment?) OTOH: it should be impressive for people.
It is difficult to do an experiment, cheaply, that demonstrates, unambiguously, the main points of QM. None of the ideas in post #6 involve quantum physics much at all.
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