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How to use chocolate and a microwave to measure the speed of light. Experimental results and anaylsis included.

Date : 20/03/2017

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Uploaded by : Anand
Uploaded on : 20/03/2017
Subject : Physics

Though the speed of light may be set in stone, that doesn t stop us from measuring it. This report aims to present a way of measuring the speed of light using ordinary everyday objects. Although the experiment and measurements themselves are simple enough, the physic and reasoning behind them is quite complex. This report not only aims to show how to measure the speed of light, but also explain how this is done.


The speed of light is now defined as 299 792 458 meters per second. This is true, since the meter is defined as the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. And a second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the Caesium 133 atom.

Therefore, measuring the speed of light is in a sense meaningless. What we want to prove however, is that to do experiments you don t require cutting edge equipment, rather the desire to experiment and imagination. This also means that we can focus on other issues, such as errors, inconsistencies and the method itself. This is because we already know the end result of the experiment.

Experimental method and results:

For this experiment we require two things, chocolate and a microwave. First we must check the frequency of the microwaves emitted by the magnetron. The microwave used in this experiment uses a = 2.45 GHz microwaves.

Another important issue is the chocolate. In our measurements we used cheap Tesco everyday value chocolate . Apart from brand the kind of chocolate is also important. In our experiment we used both milk and dark chocolate.

I theorized that since dark chocolate would be more difficult to melt it would produce more accurate measurements, however this was not the case.

The next step is removing the revolving plate from the microwave, since we want the chocolate bar to be stationary.

After putting the chocolate in the microwave oven, heat up 15-30 seconds, depending on the power output of the microwave oven.

Next comes the core of the experiment, the measurements. Simply measure the distance between points A and B as shown in Diagram 1. Note that the melted Diagram 1. may be in different positions.

By measuring the distance between the hot spots we find the half-wavelength of the microwave radiation, which is in fact light. This is because microwaves use standing waves to heat up food.

We can get results for the speed of light by multiplying the distance measured times the frequency used by the microwave. In measuring the distance we have to be mindful that high precision is not necessary as it will not affect accuracy. This is because it is difficult to determine the exact location of the center of the melted spots. Due to this fact the estimated error in measuring the distance is over 2 cm, which means an error of over 17% in the measurement of the speed of light.

This resource was uploaded by: Anand