# Fun Physics you can do at home.

Gold Member

## Main Question or Discussion Point

The first one I got from a book by New Scientist.

For the first experiment you need a microwave oven, a chocolate bar and a ruler.
You can use these to find the speed of light ($$c\ =\ 2.99792458\ \times\ 10^{8}\ m\ s^{-1}$$). Take the rotating tray out your microwave oven and place the chocolate bare inside and turn it on. You should start to see hot spots appear on the chocolate bar, this is because the microwaves don't heat evenly if it isn't rotating. Take the chocolate bar out the microwave oven and use your ruler to measure the distance between 2 hot spots, then look in your microwave oven user manual to find the frequency of the wave. Finally use the equation v=f$$\lambda$$ and you should have a value close to the speed of light. (If not you can still eat the chocolate).

The second experiment is more dangerous. You need a metal fuel can, a fire or BBQ, a pole to pick up the fuel can and what ever you feel you need to keep your self safe (gloves, goggles etc). You put some water in the can but not enough to make it so heavy you can't lift it easily, you then put it on the fire with the cap off/open. When the water boils lift the can off with the pole, then close the cap (using gloves) and stand well back. As the can cools down the pressure in the can drops and the weight of the atmosphere with begin to crush the can.
(This experiment can be quite dangerous so do it sensibly, don't try it inside)

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The first one I got from a book by New Scientist.

For the first experiment you need a microwave oven, a chocolate bar and a ruler.
You can use these to find the speed of light ($$c\ =\ 2.99792458\ \times\ 10^{8}\ m\ s^{-1}$$). Take the rotating tray out your microwave oven and place the chocolate bare inside and turn it on. You should start to see hot spots appear on the chocolate bar, this is because the microwaves don't heat evenly if it isn't rotating. Take the chocolate bar out the microwave oven and use your ruler to measure the distance between 2 hot spots, then look in your microwave oven user manual to find the frequency of the wave. Finally use the equation v=f$$\lambda$$ and you should have a value close to the speed of light. (If not you can still eat the chocolate).
Okay, so then the distance between the spots is the wavelength? If it is a microwave then surely it must be emitting microwaves, therefor the all microwaves must have a similar frequency. If so we would expect the spots to be between 1mm - 300mm? Have you tried this by any chance? I know my chocolate isn't worth risking

dst
Use marshmallows, chocolate is just too precious

We actually did this in class. And yes, it works but it's a bit silly considering that c must already have been known to create the microwave. Like measuring a thermometer against a thermometer.

Gold Member
Well the book i got it from said it works. My microwave has the rotating plate built into the back of it so the food is still and the emitters move, so when I put my chocolate in it all just melted :rofl: As for the second one I have tryed that, but its hard to get it off the fire and close the lid.

Use marshmallows, chocolate is just too precious

We actually did this in class. And yes, it works but it's a bit silly considering that c must already have been known to create the microwave. Like measuring a thermometer against a thermometer.
Well then could we not do the same thing with the sun and UV rays? If we knew the frequency of that then we could determine the speed of light. The problem I guess is that it would depend on what degree of accuracy you used, though I am perfectly aware this isn't how it would be calculated usually.

I think that the distance between two spots won't be the wavelength: you have standing waves in the microwave, so that the distance between two nodes would be fractions of the wavelength depending on the mode...

Gold Member
Well the chocolate may be pointless but you can eat it at the end, but the fuel can one is much better. It gives you a good idea how much the earth atmosphere weighs.