# Wavelength, Frequency, and Planck's Constant

by Soaring Crane
Tags: constant, frequency, planck, wavelength
 P: 484 1) What is the wavelength (in meters) of an electromagnetic wave of frequency 2812571875.00MHz? Example: 1.11e-5 LAMBDA = c/v =(3.00*10^8 m/s)/(2812571875.00MHz*10^6 Hz/MHz) = 1.07E-7 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) = 4.23E-1 m?? _________________________________________________________________ 3) How much energy is carried by a mole of photons with frequency 704.00MHz? Give your answer in kilojoules per mole, Example: 1.11e-5 Careful with your conventions. E = hv =(6.626*10^-34)*(704.00MHz*10^6 Hz/MHz) = 4.665E-25 J 4.665E-25 J(1 kJ/10^-3 J)* (6.02*10^23 photons/1mol) = 2.81E-4 kJ/mol?? _________________________________________________________________ Did I express my answers with the right significant digits and calculations? Thanks.
 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.
 Mentor P: 7,320 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?
PF Gold
P: 7,120
Wavelength, Frequency, and Planck's Constant

 Quote by Integral 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?
I suppose its because he's using a text book and I bet he might get the answers wrong (as far as grading is concerned) if he starts using different sources for the numbers.
HW Helper
P: 1,326
 Quote by Soaring Crane 1) What is the wavelength (in meters) of an electromagnetic wave of frequency 2812571875.00MHz? Example: 1.11e-5 LAMBDA = c/v =(3.00*10^8 m/s)/(2812571875.00MHz*10^6 Hz/MHz) = 1.07E-7 m??
If your text does give constant c to more significant digits, I would use them as Integral suggests. If you are not given speed of light in your text, you can use any valid source such as NIST (national institute of standards & technology). An equally correct answer to this part is 107nm. If your question does not specify units for your answers, both solutions are good.

 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) = 4.23E-1 m??
I would check this again, especially your decimal place.

 3) How much energy is carried by a mole of photons with frequency 704.00MHz? Give your answer in kilojoules per mole, Example: 1.11e-5 Careful with your conventions. E = hv =(6.626*10^-34)*(704.00MHz*10^6 Hz/MHz) = 4.665E-25 J 4.665E-25 J(1 kJ/10^-3 J)* (6.02*10^23 photons/1mol) = 2.81E-4 kJ/mol??