Materials:
Microwaves use a type of radiation called, you guessed it, microwave radiation. It is an electromagnetic wave just like visible light. You can learn more about radiation here. But basically, microwaves and everything else move in a sinusoidal shape that
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l | m l s
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The high points are called peaks and the low points are called troughs. There are several things used to describe this type of wave. One is amplitude. That is the height, represented by the dashed vertical red line. Another is wavelength, the length of one complete "wave", and one wavelength is underlined in the above picture. Wavelength is commonly represented by a lambda. The last is the frequency (represented by a nu). Frequency is the number of times a wave passes a certain point in a certain amount of time. If that time is measured in seconds, the unit for frequency is Hertz (Hz) which is 1/seconds.
All sinusoidal waves can be described with these properties I just described. There are several equations to relate these. The one we are interested in right now is frequency*wavelength = speed. Think about why this makes sense. Speed is distance traveled over time. So take a certain point on the wave, and see how long it takes to travel a certain distance. Frequency is number of times a certain point is passed in one second. Wavelength is the length. So frequency times wavelength is length of one "wave" times number of times it traveled that length over time. In other words, distance over time.
The two melted spots in your chocolate and your marshmallows represent two points on the plane in the center of the wave (like the blue l and s). So the distance between them is half a wavelength. As I said above, your microwave probably has a frequency of 2.45 gigahertz (which is 2.45 x 10^9 hertz), but feel free to verify that for your particular model. Can you know figure out how to calculate the speed of light?
Here it is:
(length between 2 melted spots IN METERS *2) * (2.45 x 10^9 herz) = the speed of light
wavelength * frequency = speed
For example, when I did it I had 0.065 m * 2 * 2.45x10^9 = 3.19x10^8 m/s. Not bad.
Why did the units have to be in meters and hertz instead of centimeters and gigahertz? Simply because speed in normally measured in meters/second so we wanted to make sure our units cancelled out properly. The actual speed of light is 3 x 10^8 m/s. Well, strictly speaking it's 299,792,458 m/s but we are definitely not getting that level of accuracy here. We microwaved both the chocolate and the marshmallows so we could have two data points. Which one was closer, and how accurate were your results?
Now hopefully your marshmallows and chocolate didn't cool while you were doing all these calculations. If they did heat them up again, and eat them with the graham crackers. So you can now tell all you friends you measured the speed of light with a s'more.
- Chocolate
- Marshmallows
- Microwave (you will need to know the frequency. If you can't find it the norm is 2.45 GHz)
- Ruler
- Something to do calculations on
- Graham Crackers
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| The red circles are the melted spots. |
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| Image courtesy of Null Hypothesis |
Microwave it for a bit, until there are 2 melted patches. 20 seconds should work. Now remove it from the microwave and use your ruler to measure between the two melted spots. Spread the marshmallows out on a plate and repeat.
s
k | e t
o | s k h
o | o i i
l | m l s
e
t g
h n
i
The high points are called peaks and the low points are called troughs. There are several things used to describe this type of wave. One is amplitude. That is the height, represented by the dashed vertical red line. Another is wavelength, the length of one complete "wave", and one wavelength is underlined in the above picture. Wavelength is commonly represented by a lambda. The last is the frequency (represented by a nu). Frequency is the number of times a wave passes a certain point in a certain amount of time. If that time is measured in seconds, the unit for frequency is Hertz (Hz) which is 1/seconds.
All sinusoidal waves can be described with these properties I just described. There are several equations to relate these. The one we are interested in right now is frequency*wavelength = speed. Think about why this makes sense. Speed is distance traveled over time. So take a certain point on the wave, and see how long it takes to travel a certain distance. Frequency is number of times a certain point is passed in one second. Wavelength is the length. So frequency times wavelength is length of one "wave" times number of times it traveled that length over time. In other words, distance over time.
The two melted spots in your chocolate and your marshmallows represent two points on the plane in the center of the wave (like the blue l and s). So the distance between them is half a wavelength. As I said above, your microwave probably has a frequency of 2.45 gigahertz (which is 2.45 x 10^9 hertz), but feel free to verify that for your particular model. Can you know figure out how to calculate the speed of light?
Here it is:
(length between 2 melted spots IN METERS *2) * (2.45 x 10^9 herz) = the speed of light
wavelength * frequency = speed
For example, when I did it I had 0.065 m * 2 * 2.45x10^9 = 3.19x10^8 m/s. Not bad.
Why did the units have to be in meters and hertz instead of centimeters and gigahertz? Simply because speed in normally measured in meters/second so we wanted to make sure our units cancelled out properly. The actual speed of light is 3 x 10^8 m/s. Well, strictly speaking it's 299,792,458 m/s but we are definitely not getting that level of accuracy here. We microwaved both the chocolate and the marshmallows so we could have two data points. Which one was closer, and how accurate were your results?
Now hopefully your marshmallows and chocolate didn't cool while you were doing all these calculations. If they did heat them up again, and eat them with the graham crackers. So you can now tell all you friends you measured the speed of light with a s'more.
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