Changing Microwave Wavelengths?
Most recent answer: 01/11/2013
Q:
I have just completed a science fair project about different power settings of a microwave. I was wondering if the wavelength of the microwaves changes depending on the power setting, or if the way the microwave heats things up is different depending on the setting. I used the defrost setting, the normal setting, and the popcorn setting in my experiment. I microwaved egg whites, measured the distance between "hot spots" and multiplied it by 2 to find the wavelength. I got that the defrost setting had microwaves with a wavelength 0f 14.6, while the popcorn setting had microwaves with wavelengths of 17.2, regular had 17. I have no explanation for why this happened. I thought the popcorn setting would have the shortest wavelength because it would be the most powerful...Or is that not the case? Any help would be greatly appreciated!
- Elizabeth (age 14)
Virginia, USA
- Elizabeth (age 14)
Virginia, USA
A:
I'm very surprised that you found a wavelength that depends on microwave power in this nice experiment. The magnetron tubes in a standard microwave oven simply cycle on and off for different fractions of the time to give the different power levels, but while on they run at the same level. So even if somehow the magnetron frequency depended on how much power it was putting out, the frequency would be the same while it was putting out power.
Now, for a fixed frequency, the wavelength depends on the dielectric constant, so it can change a little as the material cooks. Maybe that give give slightly different values depending on how rapidly the material cooks, which depends on power setting. That still sounds unlikely to give the effect you saw.
Here's another possibility. Imagine putting a thin string of egg white along the direction the wave propagates. Your method will work well for that. Now tilt the direction of the string. You have to go farther down that tilted string to get from one hot spot to the next, so it will make the wavelength look longer than it really is. If between different runs slightly different pans etc. are used, then not only will the absolute measure of the wavelength come out off a little, so will the comparisons. Maybe that's what's up.
p.s. Those wavelengths you give are missing the units. I guess they're cm?
Now, for a fixed frequency, the wavelength depends on the dielectric constant, so it can change a little as the material cooks. Maybe that give give slightly different values depending on how rapidly the material cooks, which depends on power setting. That still sounds unlikely to give the effect you saw.
Here's another possibility. Imagine putting a thin string of egg white along the direction the wave propagates. Your method will work well for that. Now tilt the direction of the string. You have to go farther down that tilted string to get from one hot spot to the next, so it will make the wavelength look longer than it really is. If between different runs slightly different pans etc. are used, then not only will the absolute measure of the wavelength come out off a little, so will the comparisons. Maybe that's what's up.
p.s. Those wavelengths you give are missing the units. I guess they're cm?
(published on 01/11/2013)