The speed of light and marshmallows

The speed of light and marshmallows

Demonstration

By Ernest Ventura

Equipment Involved:

A) microwave oven

B) marshmallows or any other microwavable food that melts easily

C) microwavable container

D) ruler

Time Requirements:

>1 minute to set up equipments

>1 minute to perform demonstration

References:

1. About.com

Measure the Speed of Light with Chocolate & a Microwave by Joseph Andersen

http://physics.about.com/cs/opticsexperiments/a/290903.htm

2. Finding the Speed of Light with Marshmallows by Robert H. Stauffer

http://www.physics.umd.edu/ripe/icpe/newsletters/n34/marshmal.htm

Description:

This project demonstrates how to verify the speed of light using a microwave oven and marshmallows

Procedure:

1) Remove the turntable from the microwave oven so we can measure the hotspots or antinodes of the microwave.

2) Microwave the marshmallow for about 20 seconds. Just enough time to see 4-6 spots where it begins to melt.

3) Measure the distance between the melted spots. This is half the wavelength of the microwaves generated inside the oven while operating.

How it works?

When you turn on your microwave oven, electrical circuits inside start generating microwaves. These waves bounce back and forth between the walls of the oven, the size of which is chosen so that the peaks and troughs of the reflected waves line up with the incoming waves and form a “standing wave”.

A full wave is shaped like a “sine function”. The distance between the maximum displacements of the wave is one half the wavelength.

The electromagnetic field inside the microwave behaves in simple harmonic motion. At the antinodes where the vibrations are greatest, you will see the greatest heating, while at the nodes, the heat is not as much.

Thus, the distance between the melted regions is equal to the distance between the antinodes or equal to half the wavelength

Repeatability:

Results are consistent when using the same microwave oven and melting the same food. Instances that gives a different measure for the quantity “half-wavelength”:

A) when using the same microwave but melting different food.

b) When melting the same food but using different microwave oven. This is probably due to the different specifications by different manufacturers.

Evaluation:

Complexity: the speed of light is very complex. What’s going on inside the oven while operating is also very complicated because we really don’t see microwaves. How the melted spots in the marshmallows and the distance between them represents half the wavelength of the microwave is also not so easy to understand. This demonstration is very easy given that things work well. This is undoubtedly one of the if not the easiest way to approximate the value c (speed of light).

Repeatability: This experiment should be consistent because the only possible human error that can alter the results is measuring the distance between the melted spots. The microwave oven usually works the same every time so the approximated value of c given by this experiment is either consistently inaccurate or consistently close.

Efficiency: Microwave oven can be found in almost every household. Marshmallows, chocolates, or even cheese can even be eaten after the experiment is done. There is no other way that I can think of to approximate the vale of c any easier, faster, and less expensive than this.

Safety Factor: there is a probably unnecessary but recommended precaution of placing a half glass of water in the microwave – if there is insufficient material in a microwave, you can blow the internal fuses, rendering the microwave inoperable. However, as the microwave then had to heat the water as well, the melting process took longer.

Interesting: First I was so amazed of “pi”, then there was Euler’s number. Now I have c. These three constants of the universe are amazing. Not only c is a finite value, it is a universal constant and a speed limit.

Physics-related: Light, optics and modern (contemporary) physics

Overall quality: 10/10

Formulas Involved: speed of light = wavelength * frequency (c=λ*f)