Radiometer Speedometer

A radiometer measures light intensity by propelling absorbing and non-absorbing panels within a vacuum. Here I made quantitative measurements of intensity by imaging the motion onto a photocell and then timing the resulting signal with a digital oscilloscope. wikipedia

Here I had all of the pieces at hand. The invention was to assemble them and turn out all the lights except for the one on the radiometer. I focused the arrangement by placing a white index card in front of the photocell so I could see the inverted image clearly.

I often made sketches like this by drawing on index cards, scanning the images and then coloring them with an image editing tool. There is a lot of physics present in this diagram, including the wrong assumption that light travels in rays. Feynman explains this in some detail for laymen in his book, QED. wikipedia

Here Feynman explains why some spend their career answering simple questions like how light moves.