How Many Photons Are Reaching Your Radio When Listening to 100 MHz FM Station?

In summary, the small number of radio photons that reach our ears per second is due to the radio signal's power and the distance of our receiver from the antenna.
  • #1
clarkandlarry
20
1

Homework Statement



If electromagnetic radiation is made up of quanta, why don't we detect the discrete packages of energy, for example, when listening to the radio?

Homework Equations



N/A

The Attempt at a Solution



Does it have anything to do with the type of wavelengths or the lengths of the wavelengths?
 
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  • #2
What exactly do you mean by detect?
 
  • #3
Hi clarkandlarry! :smile:
clarkandlarry said:
If electromagnetic radiation is made up of quanta, why don't we detect the discrete packages of energy, for example, when listening to the radio?

Does it have anything to do with the type of wavelengths or the lengths of the wavelengths?

No.

Hint: compare with similar problems:

Why don't we detect individual photons with our eyes?

Why don't we detect individual electrons with an ammeter? :smile:
 
  • #4
So it is because the lengths of the wavelengths are so small our ears are unable to detect the packets of energy?
and what exactly do you mean by the "types" of wavelengths?
 
  • #5
clarkandlarry said:
... what exactly do you mean by the "types" of wavelengths?

Why are you asking us? You introduced that phrase in your initial post.
 
  • #6
im asking that because i don't know what 'types' of wavelengths there are
 
  • #7
Surely it has something to do with the fact that your ears are designed to detect pressure fluctuations and your eyes are designed to detect E/M waves (over a VERY limited frequency range), and the two generally don't mix? We humans can't see individual photons since it takes at least two or three photons to trigger the nerve impulse in the retina.
 
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  • #8
There are a whole range of wavelengths for light, going from the very small [tex]\lambda=(roughly)\ 10^{-8}m[/tex] to the very large [tex]\lambda=1m[/tex] all with a corresponding frequency and energy. The same is true for sound waves, although the relationship between frequency wavelength and energy is not as straight forward.
 
  • #9
clarkandlarry said:
im asking that because i don't know what 'types' of wavelengths there are

The wavelength of electromagnetic waves could theoretically be any length whatsoever, i.e. anything between 0 meters and infinity meters. For radio waves, it will be in a narrower range corresponding to radio wave frequencies.

But that's not really relevant to this problem.

This has more to do with how often individual radio-wave quanta are received by a typical radio.
 
  • #10
Ask yourself this question: just how many photons are reaching your radio every second when you listen to your favorite station? You have an equation for the energy of a single photon in terms of its frequency. So pick a convenient radio frequency, say, 100 MHz (i.e., "100 on your FM dial") and calculate the energy of a single photon.

Now consider the power of the radio signal being sent out. For a typical commercial station, this can easily be 10 kW. So how many 100-MHz radio photons is the station's antenna emitting every second?

Pick some reasonable distance of your receiver from the antenna, for instance, 10 km. Assume the radiation of this photons is distributed equally in all directions ("isotropic emission") and figure out how many photons are crossing a 1 square meter area on a 10 km. sphere each second. (This is the "intensity" of the radio signal at your receiver). For convenience, you could take this as the number of radio photons you are intercepting every second. Does one photon more or less matter much compared to that number? If it does, you can "detect" the individual quanta of radio energy. If not,...
 

What is electromagnetic radiation?

Electromagnetic radiation is a form of energy that is produced by the movement of electrically charged particles. It is characterized by electric and magnetic fields that oscillate at right angles to each other and travel through space at the speed of light.

What are the different types of electromagnetic radiation?

The different types of electromagnetic radiation are radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. They are all part of the electromagnetic spectrum and differ in their wavelengths and frequencies.

How does electromagnetic radiation interact with matter?

When electromagnetic radiation encounters matter, it can be absorbed, reflected, or transmitted. The interaction depends on the properties of the material, as well as the wavelength and intensity of the radiation.

What are the health effects of exposure to electromagnetic radiation?

Exposure to high levels of electromagnetic radiation, such as X-rays and gamma rays, can be harmful to living organisms. However, the levels of electromagnetic radiation emitted from everyday sources, such as cell phones and Wi-Fi, are not considered to be harmful.

How is electromagnetic radiation used in everyday life?

Electromagnetic radiation has a wide range of applications in everyday life. Radio waves are used for communication, microwaves for cooking, infrared radiation for remote controls, visible light for vision, and X-rays for medical imaging. It is also used in technologies such as radar, GPS, and Wi-Fi.

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