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Wavelength, Frequency, and Planck's Constant 
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#1
Nov305, 03:08 PM

P: 484

1) What is the wavelength (in meters) of an electromagnetic wave of frequency 2812571875.00MHz?
Example: 1.11e5 LAMBDA = c/v =(3.00*10^8 m/s)/(2812571875.00MHz*10^6 Hz/MHz) = 1.07E7 m?? _________________________________________________________________ 2) What is the wavelength (in meters) of an electromagnetic wave of frequency 7084.00MHz? LAMBDA = c/v =(3.00*10^8 m/s)/(7084.00MHz*10^6 Hz/MHz) = 4.23E1 m?? _________________________________________________________________ 3) How much energy is carried by a mole of photons with frequency 704.00MHz? Give your answer in kilojoules per mole, Example: 1.11e5 Careful with your conventions. E = hv =(6.626*10^34)*(704.00MHz*10^6 Hz/MHz) = 4.665E25 J 4.665E25 J(1 kJ/10^3 J)* (6.02*10^23 photons/1mol) = 2.81E4 kJ/mol?? _________________________________________________________________ Did I express my answers with the right significant digits and calculations? Thanks. 


#2
Nov305, 03:53 PM

PF Gold
P: 7,120

Yes, the significant digits look correct and the calculations seem correct although I don't have a calculator around at the moment.



#3
Nov305, 05:03 PM

Mentor
P: 7,319

You are given a lot of signifiant digits in your problem, why did you only use 3 for c? Is that c to 3 digits? There are about 8 digits of c available, why not use them?



#4
Nov305, 05:06 PM

PF Gold
P: 7,120

Wavelength, Frequency, and Planck's Constant



#5
Nov305, 06:06 PM

Sci Advisor
HW Helper
P: 1,326

You should have (1 kJ/10^3J), using your equation as written, you would get 281 kJ/mol 


#6
Nov405, 05:17 AM

P: 484

For #2, it is 4.23E2 m?
For the constant c, my textbook gives the value in 8 decimal places, but it says that it is mostly rounded off to 3.00*10^8 and it uses this rounded off version in examples. 


#7
Nov405, 05:21 PM

Sci Advisor
HW Helper
P: 1,326

Nice job on #2 !! Try solving your questions, more than one way. Then you will be able to catch things like this on your own.
If they use the rounded off version of c in their examples, for practical purposes, you probably can use it as well. If you're in doubt, ask your teacher first before handing in those questions.. 


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