How to Measure the Speed of Light Using Chocolate, a Microwave and a Ruler

It took over 300 years of experimentation and refinement to arrive at the figure for the speed of light which we use as standard today. That being the case, the method proposed below for determining that speed yourself might seem more than a little surprising.


All you need is some kind of food that can melt (chocolate is good but you can also use marshmallows or cheese), a microwave oven, a microwave-safe dish to put the food in, and a ruler.

Place the food on the dish.
Remove the turntable from the microwave – it’s important that the dish can’t move.
Put the dish in the microwave.
Cook on a low heat until it’s clear the food is beginning to melt in spots.Begin by trying 30 seconds.
These spots relate to the peaks of the ‘wave’ – the distance between two peaks is half a wavelength.
Once the melted spots appear, remove the dish and measure the distance between the centres of these spots. You should observe that one distance should repeat again and again.

Now look on the microwave (it might be on the back) to find its frequency – this is typically 2.45GHz. We know that
  c = λv  , or the speed of light = wavelength multiplied by frequency.

So, v is the frequency of the microwave. If it’s 2.45GHz then the figure you will use in your calculation will be 2,450,000,000 (whatever the frequency listed is, it will almost certainly be in gigahertz – 1GHz is 1,000,000,000 so make sure your calculation reflects that). You now need to multiply this by λ, which is double the distance you measured in metres (for example 15cm is 0.15 metres). See how close to the true speed of light, 299,792,458 m/s , you can get.


Speed of Light  =  Distance Measured    X    Microwave Frequency

Author: Robert

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