Speed of light in the microwave with Magic Stars

 I took the turntable out of a microwave and put in wooden blocks.

I placed Magic Stars on greaseproof paper on top of a heat proof mat and balanced it on the wooden blocks. I shut the door and turned on the microwave.

If you use your imagination, you can see that in some places the chocolate is more melted than in others. The non-melted bits represent places where the wave has not been going up and down. Technically they are called nodes. We have made a stationary wave - not a GCSE term - so to measure the wavelength, it is not just from one melted bit to the next but you need to go across to the melted point after that. So you are measuring across two sections of non-melted stars. I reckoned it was about 10cm. I read the frequency from the back of the microwave - it was 2450 MHz. I used the equation wave speed = frequency x wavelength = 2450 000 000 x 0.10m = 245 000 000 m/s. The true speed of light is 300 000 000 m/s so I was pleased to be so close with such an inexact experiment.