# The question of the century

1. Nov 13, 2004

### sigma

Hi! See if you can answer this:

Yesterday me and my friend measured the frequency of a microwave owen. Our experiment indicated 2300 MHz while the "right" answer, found on a sign on the back of the apparatus, showed 2450 Mhz. Our error hence: ~6%.

I find this pretty impressive, as I hope you do too, concidering the equipment we used:
a ruler and some marshmallows

The question is therefore:
How does one measure the frequenzy of a microwave owen using a ruler and marshmallows?
Let's see if somone can figure out how we did this!

Cheers

2. Nov 13, 2004

### Staff: Mentor

Usually this fun experiment is used to determine the speed of light using a micowave, marshmallows, and a ruler. But, if you assume the speed of light, you can measure the frequency.

What you actually measure is the distance between melted marshmallows, which is the distance between the anti-nodes of the microwaves, and thus is half the wavelength. Use the wave equation ($c = \lambda \nu$) to find the frequency.

Good fun!

3. Nov 13, 2004

### sigma

Aww. So soon. Okay you were right. Congrats!
We were lucky because the wavelenght was almost precisly half the distance between the walls, I assume this made the resultant wave more articulated.

We also noticed that the marshmallows got hot in a sort of "checkboard pattern". This led us to the conclusion that a wave of identical wavelength must be traveling from the back of the owen, interfering with the perpendicular wave to form the pattern. As far as we know, there's just one whatever they're called (it's a sort of wide-beam electron cannon, right?) in the owen. Can somone explain this?

4. Nov 13, 2004

### Staff: Mentor

Someone actually brought this up a few days ago - I hadn't heard of it before.

5. Nov 13, 2004

### sigma

Well I read about wave interference in microwave owens on a webpage and found the marshmallow thingo some place else. The precision of it was way better than expected, or perhaps we were just lucky?