You will need:
- A bar of chocolate
- Microwave
- Ruler & calculator
- A plate and potentially a flat bottom dish too
- Adult help
- BTW: if you don’t have chocolate you can also use cheese slices
Remove the microwave turntable and then ring with wheels from the microwave.
Place your chocolate bar on a ceramic plate and put this into the microwave. You might find that adding a flat plastic dish will help raise the plate above the turntable motor.
NB: Don’t use metal or metal-rimmed plates inside your microwave!
Run the microwave for around 20 seconds and then look to see if there are any melted spots on the chocolate bar.
Repeat until you get melted spots but don’t go so far as to burn the chocolate!
Be careful at this point, the chocolate is hot!
Use a ruler to measure the distance between the middle of two adjacent melted spots of chocolate. You should find that there are several places to take this measurement and so you could take the average between different melted spot pairs.
What you have measured is 1/2 the wavelength of light! Read below to work out the speed of light using chocolate and a little bit of mathematics.
Don’t let the chocolate go to waste 🙂
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What is going on?
The speed of light in a vacuum, also known as c, is a universal physical constant that scientist use in many calculations (including the famous E=mc2). Its exact value is defined as 299,792,458 metres per second. To work out the speed of light using chocolate, we need to work out the wavelength of the microwaves inside. Once we know this we can use the following formula to work it out;
c =λf
where
c = speed of light
λ = the wavelength of light, usually measured in meters
f = the frequency at which light waves moves (hertz)
Different microwaves have different power levels, however if your microwave is a standard model it should have a frequency of 2.45 gigahertz. This means that the microwaves inside move up and down 2.45 billion times per second.
To work out the speed of light using chocolate and a microwave,
-
- Firstly, multiply the distance between the melted spots on the chocolate bar by two. The reason for this is that the distance between the two melted spots was 1/2 a wavelength and need to get the full wavelength. See the image again here;
Assuming your microwave is running at 2.45 gigahertz, multiply that number by 2,450,000,000 (2.45 gigahertz expressed as hertz ). Remember, 1 Gigahertz is a measure of frequency equivalent to one thousand million (109) cycles per second i.e 1 billion. 1 hertz just means one cycle of the wave. If you’re not sure of the frequency of your microwave, check your microwave manual - This answer works in centimetres per second so you’ve got one more step. To get an answer in metres per second, divide this answer by 100.
- Firstly, multiply the distance between the melted spots on the chocolate bar by two. The reason for this is that the distance between the two melted spots was 1/2 a wavelength and need to get the full wavelength. See the image again here;
In summary, the speed of light in chocolate (for this microwave) is calculated as follows:
c = distance between two melted spots of chocolate x 2 x 2450000000 / 100
What answer do you get for c? Was it close? In our example above we measured an average of 6.2 cm between each melted spot of chocolate and so our calculation ends up being 303,800,000 metres per second which isn’t exactly 299,792,458 metres per second but it’s not too bad either. Plus, we get to each the chocolate afterwards!
Variables to test
- Does it matter where you place the chocolate within the microwave?
- What if the chocolate is higher or lower within the microwave?
- What happens if the chocolate is spinning on the turntable during the activity? Why?
- Try different microwave types, does this matter?
- Try doing this with cheese slices, is it easier to measure?
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The standing wave is moving up and down. The point of maximum energy is the antinode. The node has no energy. I don’t think you visual diagram is correct. The point of melting is the antinode. The result of your calculation is, of course, correct, but you are measuring the distance between the antinodes, not the nodes.
Yep, you’re right! Graphic design off and it got missed. Thanks!