Homework Help: Chemistry

Posted by Frank on Monday, February 27, 2012 at 12:41am.

I'm having a difficult time with the Conversion Units in my equation.

Attempting to answer this question:

My cell phone has an antenna about 10.00cm long. If this is one quarter of the wavelength of the radiation, at what frequency in Megahertz does it operate? Note that cell phones, like radio, transmit sounds via electromagnetic waves which travel at the speed of light or 3x108m/s.

I know f=v/l, but Ii am having a difficult time in getting to an answer in MegaHertz.

Chemistry - DrBob222, Monday, February 27, 2012 at 1:01am
c = speed of light = 3.00E8 m/s
f = freq is in Hz
w = wavelength in meters.
c = fw

1/4 wavelength = 10.0 cm so 1 w = 40 cm = 0.400m
f = c/w = 3.00E8/0.4 = 7.50E8 Hz.
Now you convert to the unit you want.
7.50E8 Hz x (1 MHz/10^6 Hz) = ?
Chemistry - Frank, Monday, February 27, 2012 at 6:01am
Dr Bob,
Thanks for the help with the conversion. I was missing the solution on two fronts. One was the wavelength factor and the other was the MegaHertz.

Do you know where I can find more information on "wavelength of the radiation" ? There is not a lot of specific detail in my text book.
Thanks again.
Chemistry - DrBob222, Monday, February 27, 2012 at 2:27pm
No I don't, other than the obvious of using google.com. The c = fw thing I remember from freshman physics many long years ago but I've used it thousands of times. If you know that it will take you a long way in frequency/wavelength problems.

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