Find wavelength of a quantum of electromagnetic radiation


by trivk96
Tags: electromagnetic, quantum, radiation, wavelength
trivk96
trivk96 is offline
#1
Mar26-12, 08:03 PM
P: 47
1. The problem statement, all variables and given/known data
A quantum of electromagnetic radiation has
an energy of 0.877 keV.
What is its wavelength? The speed of light
is 2.99792 10
8 m/s, and Plancks constant
is 6.62607 10−34J s.
Answer in units of nm


2. Relevant equations
E=hf
v=fλ
... λ=v/(E/h)

3. The attempt at a solution

When i solved, i got 1.413728e-9 nm... I have checked my units. can some just help and point me in the right direction
Phys.Org News Partner Science news on Phys.org
SensaBubble: It's a bubble, but not as we know it (w/ video)
The hemihelix: Scientists discover a new shape using rubber bands (w/ video)
Microbes provide insights into evolution of human language
Dickfore
Dickfore is offline
#2
Mar26-12, 08:29 PM
P: 3,015
v is usually written as c when one speaks of the speed of light in vacuum. Also, the double fraction reduces to:
[tex]
\frac{c}{\frac{E}{h}} = \frac{h \, c}{E}
[/tex]
For this answer, you need to know the conversion factor between an electron-volt (eV) and a joule as energy units. Do you know it?
trivk96
trivk96 is offline
#3
Mar26-12, 08:32 PM
P: 47
Quote Quote by Dickfore View Post
v is usually written as c when one speaks of the speed of light in vacuum. Also, the double fraction reduces to:
[tex]
\frac{c}{\frac{E}{h}} = \frac{h \, c}{E}
[/tex]
For this answer, you need to know the conversion factor between an electron-volt (eV) and a joule as energy units. Do you know it?

Yes i did convert it but i still got it wrong

Dickfore
Dickfore is offline
#4
Mar26-12, 08:33 PM
P: 3,015

Find wavelength of a quantum of electromagnetic radiation


how did you convert it, and what did you get?
trivk96
trivk96 is offline
#5
Mar26-12, 08:36 PM
P: 47
I did it again and i got 1.414E-8 ... and i think that is in meters. Am i right??

so that means that the answer is14.14nm
_______________________________________________________________________ _

I used plancks constant in eV's. Its on the ap equation sheet
Dickfore
Dickfore is offline
#6
Mar26-12, 08:41 PM
P: 3,015
I didn't get that. What did you get for the energy in joules?
trivk96
trivk96 is offline
#7
Mar26-12, 08:45 PM
P: 47
1.405109518e-16 J
Dickfore
Dickfore is offline
#8
Mar26-12, 08:51 PM
P: 3,015
This is correct. Now:
[tex]
\frac{h \, c}{E} = \frac{6.626 \times 10^{-34} \, \mathrm{J} \cdot \mathrm{s} \times 2.998 \times 10^8 \, \mathrm{m} \cdot \mathrm{s}^{-1}}{1.4051 \times 10^{-16} \, \mathrm{J}}
[/tex]

The product and ratio of the mantissas, gives:
[tex]
\frac{6.626 \times 2.998}{1.4051} = 14.14
[/tex]
The exponents sum up to [itex]-34 + 8 - (-16) = -10[/itex]. You may read off the units from the above fraction fairly easily.

What should the answer be in scientific form?
trivk96
trivk96 is offline
#9
Mar26-12, 08:58 PM
P: 47
so in nm, it would be 1.414
Dickfore
Dickfore is offline
#10
Mar26-12, 09:03 PM
P: 3,015
yes, except that you need to use as many significant figures, as there are in variable with the least number of significant figures given in the problem. Fundamental constants are usually known to a lot of significant figures.
trivk96
trivk96 is offline
#11
Mar26-12, 09:21 PM
P: 47
Thank You


Register to reply

Related Discussions
Heat is electromagnetic radiation OR heat is __spread by__ electromagnetic radiation? Classical Physics 2
Max wavelength of CMB radiation Cosmology 4
Electromagnetic Induction vs. Electromagnetic Radiation Classical Physics 17
Wavelength of an Electromagnetic wave General Physics 4
Wavelength of electromagnetic radiation Chemistry 2