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Calculating energy in cm-1

The question is to calculate the energy of a laser light and give the answer in cm-1.

The wavelength = 541.4 nm.

Would I use

Energy = 1/λ = 1/541.4 x 10^-7 cm = 1/5.414 x 10^5 = 18470.6 cm-1

OR

Energy = 2Π/λ = 1.161 x 10^-5 cm-1

Or am I going about this completely wrong?:s-smilie:
Original post by Naami
The question is to calculate the energy of a laser light and give the answer in cm-1.

The wavelength = 541.4 nm.

Would I use

Energy = 1/λ = 1/541.4 x 10^-7 cm = 1/5.414 x 10^5 = 18470.6 cm-1

OR

Energy = 2Π/λ = 1.161 x 10^-5 cm-1

Or am I going about this completely wrong?:s-smilie:


Sorry, I'm a bit confused. Why is the energy in cm-1? :confused:
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Naami
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Original post by margalo
Sorry, I'm a bit confused. Why is the energy in cm-1? :confused:


The question just states they want it in that unit :/
Original post by Naami
The question just states they want it in that unit :/


Right, I just googled it.
The question is probably referring to the wavenumber
or (angular)

From Wikipedia:
"For electromagnetic radiation in vacuum, wavenumber is proportional to frequency and to photon energy. Because of this, wavenumbers are used as a unit of energy in spectroscopy. In the SI units, wavenumber is expressed in units of reciprocal meters (m−1), but in spectroscopy it is usual to give wavenumbers in reciprocal centimeters (cm−1). The angular wavenumber is expressed in radians per meter (rad·m−1)."

Have a look at this article: http://en.wikipedia.org/wiki/Wavenumber

So, I guess your first answer is the correct one.
I hope this helps.

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