So if you have measured 6cm and your oven operates at 2450 MHz then your measured speed of light is 012 x 2450000000 294000000 metres per second. So we take the the product of the wavelength and the frequency. Wave frequency is how many times a wave bounces up and down in one second.
You may think your microwave is good only for making popcorn or heating up last nights leftovers.
Its possible to measure the speed of light in your microwave because microwaves are really a type. We dont want the dish to rotate. And a microwave oven comes with an indication in the back that shows the frequency. Hertz the unit for frequency is the name we give to inverse seconds or 1 seconds.