Microwave Speed of Light Science Project

[Eabelaye]

My 9 year old son completed his project and collected the data for the Microwave Speed of Light Project. We are stumped on getting to a conclusion. Can someone help us understand how to use the data we collected to get to a conclusion? Is there some type of formula we need to use?

[deleted-249560]

The background section of the project explained the relationship between frequency, wavelength and the speed of a wave. When you did the experiment, you measured the wavelength of the microwaves by measuring the distance between the cooked spots on the egg.

The frequency (f), wavelength (λ, and wave speed (v) are related by the equation: v = f*λ. Since you know the frequency from the label on the microwave and the wavelength from what you measured, you can calculate the wave speed which is also the speed of light.

In this case since the speed of light is also something you can look up, if your math does pan out, post your data here and maybe we can help you figure out what happened.

Howard

[Eabelaye]

When we measured the egg we got the following measurements:
Test 1: 8 centimeters
Test 2: 9 centimeters
Test 3: 9 centimeters
I multiplied each one by the microwave frequency which was:
2450x8=19,600
2450x9=22,050
2450x9=22,050

How do I make a conclusion based on this data?

[rmarz]

Eabelaye The measured distance between the bubbles (on average) is 1/2 the full wavelength of the 2450 MHz magnetron of the microwave. The full wavelength of that frequency is about 12.2 cm (0.122 meters). If you multiply 2,450,000,000 (frequency of the magnetron in Hz) times 0.122 (wavelength) you get 298,000 meters/sec, the velocity of light. It would seem your measurement is a little off, because you would see the spacing at around 6 cm instead of the 8 and 9 cm you observed. I'm sure your microwave is 2450 MHz, so perhaps your measurement observation is off. Your figures calculate to 196,000 and 220,500 meters per second. Too slow for the actual velocity of light.

Rick Marz

[deleted-249560]

Eabelaye, this same question has come up before and the other student got data with the opposite effect (spots too close together). In fact, if you look around on the internet you'll find variants of this project that advocate using chocolate bars instead of egg white - but it's the same idea. Many people ask why they see 7 or 8cm between the spots.

Your measurements seem to turn up pretty frequently. As the project summary and the math shows, you should have expected to measure 6cm between the cooked spots. When this question came up in February (https://www.sciencebuddies.org/science- ... hp?t=14213), that student got measurements *smaller* than 6cm. I tried it then, and saw spots between 7cm and 9cm most frequently - measured with a machinist's vernier caliper. The question was: why?

My theory was that the wave stirrer in our microwave was messing up the measurement. The procedure suggests that you have a microwave with a turntable (removable) that helps keep hotspots from making your food cook unevenly. The oven in our kitchen is an older one that doesn't have a turntable, but has a reflective metal fan that's designed to prevent hotspots by bouncing the waves all over the oven. I found that I could get different results for this test by moving the plate of egg white to different areas. I then found a microwave *without* a wave stirrer and tried it. In that case, I got the 6cm measurement.

If your son measured accurately, then the data is what it is. That happens sometimes in science. In a lab you would be figuring out what caused the results you got and making changes to your procedure, equipment, materials, and trying again. He could write up the results as he got them and explain the error, or maybe try the experiment with the neighbor's microwave. I also like the idea of using chocolate - it doesn't change the results, but you can make s'mores afterwards. Just put the chocolate on a graham cracker and microwave until it just begins to melt in a few spots. Measure, write down the data, then melt it more and enjoy a well-earned snack.

Howard

[bradleyshanrock-solberg]

Agree with Howard on all points.

Data that does not get the expected result is not unusual in science, and is often more interesting. Your conclusions will tend to revolve around explaining what you saw. Spend a little time on the following thoughts, and if you can answer all three questions when a science fair Judge looks at your project, you will show good understanding of both your experiment and the scientific method.

1. What do you think is the likely reason for what you saw?
2. How would you construct an experiment to prove your explanation is correct?
3. How would you change the experimental procedure to avoid having this problem occur in future?