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Q & A: calculating wavelengths

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Most recent answer: 10/22/2007
Q:
I have two questions. 1. What is the wavelength for an FM radio signal if the number on the dial reads 102.5 MHz? 2. What is the wavelength of a radar signal that has a frequency of 33 GHz? Will you please explain how you get this answer? Thank You.
- Thomas Lee (age 15)
Gilmor Academy, Gates Mills, OH
A:
We're not going to do your homework for you, but we will say that the oscillation frequency, the wave speed, and the wavelength are related.

The oscillation frequency is the reciprocal of the amount of time it takes between one crest of the wave to go past and the next crest to go past. The wavelength is the distance between these crests. Distance divided by time is speed.

So speed = Frequency*Wavelength. You need to know what the speed of a FM radio wave is, and the speed of a radar signal. You can usually approximate that with the speed of light, but the speed of light in materials (air, for example) will be just a smidge less than the speed of light in vacuum.

MHz means millions of cycles per second.
GHz means thousands of millions of cycles per second ("billions" to Americans -- the Brits may use different words).

Tom

(published on 10/22/2007)

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