Finding the speed of light with a microwave - Science Experiment

Reason For Testing:

A reason someone might want to test the speed of light in their home is to make something more interactive and engaging as well as testing science theories themselves. If for some unusual reason the speed of light were to become unstable then you could test it in your kitchen and become a science genius.

Research:

The research involves some key concepts:

What is a wave?

Webster's dictionary defines a wave as "a disturbance or variation that transfers energy progressively from point to point in a medium and that may take the form of a variation of pressure, electric or magnetic intensity, electric potential, or temperature."

What is an electro-magnetic wave?

Electro-magnetic waves are radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge.

There is a range of frequencies in electromagnetic waves from visible light (low frequency) throught to gamma rays (high frequency. Light is only a tiny section of the electromagnetic spectrum. Microwaves have their own spectrum of electromagnetic waves (see Figure 2).

Electromagnetics waves can travel through vacuums (stuff with no matter) which means they don’t need an external medium. This is different to sound waves as sound waves are mechanical waves which means they need water or air to travel through.

For this experiment we need to find the frequency of the microwave because this frequency can be used to calculate the speed of light. If we can find the distance between the waves (the wave length) and figure out how many waves pass every second (frequency), then we can calculate how far light travels every second and therefore we can get an approximate measurement of the speed of light.

Note: Hertz (Hz) and Megahertz (MHz) are  units of measurement for wave frequencies.

Also, frequencies are invertedly proportional to wavelength so long wavelengths have a short frequency and short waves have a high frequency.

To test the speed of light I tested some of the physical properties of waves - wavelength, frequency and interference.

The interference is the electromagnetic waves bouncing off the surface of the edge of the microwave in combination with the new waves that are being created. Some are also lost in the process which also create interference. These lost waves can be heard through my radio which was near the microwave at the time.

The interference can be seen as hotspots and coldspots in the microwave. This is why microwaves have rotating platters, to spread the heat evenly.  Each cold spot (the part of the food that isn’t cooked) is equal to half a wavelength (see Figure 1 for more details). If we take out the rotating platter we can find the hot spots and therefore find the wavelength

We can find the size of the wave length by finding the distance between the uncooked portions of the food (Figure 1).  If we multiply that by two we get the full wave length of the microwave.

We have to cook the food just right so that some bits have solidify. The egg white will cook fastest in the hot areas (See Figure 1).

I will be testing egg whites in the microwave as these are relatively easy to identify the wavelength of this material.

 Figure 1

Microwave

Frequency x Wavelength (metres) = Speed Of Wave

Aim:

To find the speed of light

To use equipment found at home to measure the speed of light.

 Hypothesis:

If light is one form of electro-magnetic radiation and microwaves produce electro-magnetic radiation, then we should be able to measure the speed of light approximately using a microwave.

Equipment:

●        Microwave

●        Eggs (egg white) 3 - 6

●        Plate

●        Ruler

●        Calculator

Safety:

●        Oven Mitts

Information:

●        Frequency

Method:

 1. Find frequency of microwave oven

Mine was 2450MHz which seems to be a standard for microwave ovens but they do vary.

2. Remove rotating platter from microwave.

This is to stop heat from spreading evenly which would cancel out hot spots.

3.  Crack an egg and pour the egg whites in the middle of the plate.

Egg white shows the wavelengths well. Alternatively you can use bread with butter or chocolate to test as well.

4. Place plate in center of oven.

5. Cook materials.

30 seconds in the microwave seems to show the hotspots well.

6. Measure the space between the cooked and uncooked material to find the wave length.

The uncooked space in between is equal to half a wavelength.

7. Test multiple times.

8. Record results.

Calculate:

9. Frequency (MHz) x Wave Length = Speed Of Light

Results:

Eggs Test	Average Length 1/2 Wave (cm)	Speed of Light  (m/s)	Accuracy
Test 1	6.25	306250000	97.89%
Test 2	6	294000000	98.07%
Test 3	5.75	281750000	93.98%
Average Result From Tests (m / s)	6	294000000	98.07%
Actual Speed Of Light m / s	6.11821345cm	299792458	100%

M/s= metres per second

 Calculations:

Discussion:

●      I think that this experiment was a fair test.

Some of the difficulties I encountered arose in measuring the wavelength accurately with a ruler. This could affect the results a lot because small changes in measurement are big when multiplied by 2450 MHz.

I felt that after three tests I didn’t need to do any more. I was getting effectively the same results every time and as it turned out the measurements were quite accurate.  I averaged the results to obtain a measurement.

Conclusion:

I consider like my hypothesis was correct. The average result/calculations was only off by about 1.93% which is very close considering I used household items and products to obtain a measurement of the speed of light.

If you were to get more accurate with your measurement then you could probably measure the speed of light better - marginal differences have big effects. This project is good because it shows us that things in the home that surround us can be used to measure the speed of light.

Bibliography:

(2008, October 5). Measuring the speed of light with chocolate and a microwave oven. Morning Coffee Physics. Retrieved from http://morningcoffeephysics.com/measuring-the-speed-of-light-with-chocolate-and-a-microwave-oven/

Measure the speed of light with a chocolate bar [Video]. (n.d.). Retrieved from http://www.youtube.com/watch?v=9O2Keu6o3i0

Olson, A., & Hood N. (2007, November/December). Measuring the Speed of 'Light' with a Microwave Oven. Measuring the Speed of 'Light' with a Microwave Oven. Retrieved June 2, 2012, from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p056.shtml

Smith, C. (Director). (2009, September). Measuring the speed of light with a microwave [Video]. Retrieved from http://www.youtube.com/watch?v=cH9uHjJuANI

Tran, T. (2009). Guide to science fair. NIWA Wellington Regional Science & Technology Fair. Retrieved from http://www.sciencefair.org.nz/files/A%20Student%20Guide%20to%20the%20Science%20Fair1%20V3.pdf