# Energy lost by EM radiation per cm in air?

Hey all, is there a formula that can calculate the energy losy by a photon travelling through air at 1 atm per meter given frequency? Any help apreciated.

## Answers and Replies

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russ_watters
Mentor
Photons do not lose energy when traveling - they are what they are.

However, a photon may be absorbed and cease to exist.

jtbell
Mentor
Do you have a particular frequency range in mind? (radio, visible, X-ray, gamma-ray, ...?)

sophiecentaur
Science Advisor
Gold Member
If you google "atmospheric absorption" you may find out what you want. Your question is too unspecific for us to help you more.
Perhaps you are not concerned with a single photon?

However, a photon may be absorbed and cease to exist.
Yea, but wouldnt it be absorbed and reemitted at lower energy on average a certain number of times or would that be too capricious to be used?

Do you have a particular frequency range in mind? (radio, visible, X-ray, gamma-ray, ...?)
Yea, microwave/radio

sophiecentaur
Science Advisor
Gold Member
Yea, microwave/radio
So you are interested in radio wave propagation. There is loads of information about that and I recommend that you google appropriately to get some background and to find out the actual questions that need answering for your problem.
The attenuation of the atmosphere varies wildly over the microwave region and also with water content. There isn't a number of formula that you can just plug into and get a reliable answer. There is a lot of Statistics involved. But there are many graphs (google Images) which could give you a clue about what to expect.

NotASmurf
Thanks :)

davenn
Science Advisor
Gold Member
2019 Award
Hey all, is there a formula that can calculate the energy losy by a photon travelling through air at 1 atm per meter given frequency? Any help apreciated.
as you have been told ... forget about individual atoms ... that's irrelevant

ohhh and for the calc's below, anything less than a few 10's of metres is also going to be irrelevant
as you would be dealing with near field effects which is isn't going to be helpful to you

if you want to learn more on that google RF propagation, near field and far field

............................ Yea, microwave/radio
OK that is relatively straightforward and is used all the time for us doing pathloss calculations between radio transmit and receive sites
say example microwave links
have a look at this site and it tells you all about FSPL ... Free Space Path Loss
http://www.radio-electronics.com/info/propagation/path-loss/free-space-formula-equation.php

This will serve well for line of sight paths and for frequencies up into the mid freq microwave bands ~ 10 GHz
after 10GHz. there are additional significant atmospheric problems to deal with

cheers
Dave

NotASmurf
Thanks :)

sophiecentaur
Science Advisor
Gold Member
You should try to find stuff on 'Link Budgets". That takes everything into account; transmit power, feeder loss, antenna gain, path loss, spreading loss, etc etc and can give you a Carrier to noise ratio for the demodulated signal. Just what a chap needs. Path loss on its own is not actually a lot of use for designing a practical system.

davenn
Science Advisor
Gold Member
2019 Award
You should try to find stuff on 'Link Budgets". That takes everything into account; transmit power, feeder loss, antenna gain, path loss, spreading loss, etc etc and can give you a Carrier to noise ratio for the demodulated signal. Just what a chap needs. Path loss on its own is not actually a lot of use for designing a practical system.
the 2 popular ones are Radio Mobile and UKW Tools
I have used UKW tools for many years for my activities on 1296MHz and up to 24GHz

it takes all those factors into account

Dave

sophiecentaur