Measure the speed of light using Milky Way Stars®

Nothing travels faster than light – it only takes 8 minutes for it to reach the Earth from the nearest star, the Sun, which is 150 million kilometres away. Now anyone can measure this speed – with chocolate stars and a microwave oven! The experiment is described on a new Institute of Physics web resource for teachers about fun physics demonstrations, inspired by the Physics on Stage 2 event.

The only equipment you need for this experiment is a microwave, a ruler and chocolate, cheese or any other food that melts. Remove the turntable from the microwave and replace with chocolate on a plate (so the plate does not rotate), and heat until it just starts to melt – about 20 seconds, depending on the power of the oven. There will be some melted hot spots and some cold solid spots in the chocolate. The distance between the hot spots is half the wavelength of the microwaves, and the frequency of the microwaves will be printed on the back of the oven. The speed of light is equal to the wavelength multiplied by the frequency of an electromagnetic wave (microwaves and visible light are both examples of electromagnetic waves). So from this simple experiment, and some easy maths, you can work out the speed of light from Milky Way Magic Stars®!

The resource describes this and many more wacky, weird and most of all fun physics demonstrations, which were presented at Physics on Stage 2, a Europe-wide teachers’ event held last spring in the Netherlands.

“Measuring the speed of light by melting chocolate is just one of hundreds of physics experiments you can do at home”, said Dr Kerry Parker, a teacher and co-author of the poster. “As UK representatives at Physics on Stage 2 we had such a rich experience that we wanted to share our favourite experiments with other teachers. By putting the information on the Web, the wonderful ideas will not be forgotten.”