Homework Help: chem

Posted by lyne on Friday, January 2, 2009 at 8:45pm.

a certain substance strongly absorbs infrared light having a wavelength of 3.75痠. what is the frequency of this light in hertz?

i know that i have to use the equation c = frequency x wavelength and that c = 2.998 x 10^8 m/s. how do i convert that to 痠/s?

I think the answer will be 7.99 x 10^13, how do i find the units?

chem - DrBob222, Friday, January 2, 2009 at 9:09pm
You don't.
Use c = f x wavelength and convert 3.76 micrometers (wavelength) to meters (wavelength).
1 micrometer = 1 x 10^-6 meters
chem - Damon, Friday, January 2, 2009 at 9:09pm
The wavelength is NOT 3.75 meters
3.75 * 10^- something

distance = rate * time
so
time = distance/rate
time for one wave length to pass you =
3.75 * 10^-something/3*10^8
number that pass per second = frequency = 1/that time
so
frequency = 3*10^8/3.75*10^-something
= .8 * 10^(8+something) cycles/second or Hertz
= 8 * 10^(9+somthing)
if 9 + something = 13
then something is 4
so that original wave was 3.75*10^-4 meters long
chem -correction - Damon, Friday, January 2, 2009 at 9:12pm
= .8 * 10^(8+something) cycles/second or Hertz
= 8 * 10^(7+somthing)
if 7 + something = 13
then something is 6
so that original wave was 3.75*10^-6 meters long
chem - DrBob222, Friday, January 2, 2009 at 9:18pm
Yes, 3.75 micrometers (the old 3.75 microns) is in the infrared region. The O-H stretching frequency is about 2.75 microns so this is just slightly above that in microns.
chem - Damon, Friday, January 2, 2009 at 9:32pm
I was not about to guess micrometers was intended because the wavelength seemed long for visible light.
chem - Damon, Friday, January 2, 2009 at 9:36pm
Oh, it said infrared. I need to read more carefully.
chem - DrBob222, Friday, January 2, 2009 at 9:40pm
Right. It said infrared and it also said micrometers. The student had a computer that will make the micro symbol but mine won't do that. Damon, you're a great help on this board. I hope you continue to help.

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