# Electromagnetic Radiation

Thread Starter

#### nanobyte

Joined May 26, 2004
120
I know that visible light is a form of electromagnetic radiation. It is made of photons. A photon is a packet of energy release by an electron when it is returning to a lower enery level or orbital after previously recieving the equivalent amount of energy that makes up the photon. My question is what are the other forms of radiations (radio waves, microwaves, x-rays, etc.) are made of? Are they made of photons too, but just with different amounts of energy?

#### recca02

Joined Apr 2, 2007
1,214
yes,
it is a packet of energy for all wavelengths of radiation radio waves,microwaves, etc.
the energy of which is given by:
E=h*frequency of radiation.

h is Planck's constant.

Thread Starter

#### nanobyte

Joined May 26, 2004
120
So for example the photon of a x-ray would have more energy than the photon of visible light?

#### omnispace

Joined Jul 25, 2007
27
That's correct. The energy increases as the frequency increases and the wavelength decreases. So in order of increasing frequency we have:

Radio waves
Microwaves
Infrared
Visible Light
Ultraviolet
X-Rays
Gamma rays

These are all made of photons, but with different energy levels.

#### recca02

Joined Apr 2, 2007
1,214
and we all know how dangerous uv rays, x-rays and gamma rays are because of their high energies.

#### beenthere

Joined Apr 20, 2004
15,819
A lot of less-energetic photons can do damage, too. Microwave and strong radio frequency sources are pretty harmful.

#### recca02

Joined Apr 2, 2007
1,214
one example which makes clear that photons of different frequency have different energies
is the existence of threshold frequency of wave required for the photoelectric effect.
this effect is one reason IIRC which proved that wave theory alone is not sufficient.

#### Dave

Joined Nov 17, 2003
6,970
A lot of less-energetic photons can do damage, too. Microwave and strong radio frequency sources are pretty harmful.
Typically when people think about the danger associated with EM radiation they think of the ionising capabilities of the EM radiation, and RF and microwaves are non-ionising. That said RF and microwave can be dangerous to certain parts of the body, for example the eyes, because the heating effect induced by RF or microwaves cannot be dissipated quick enough by the blood flowing from the eyes hence causing (often significant) damage.

Dave

#### jonkopp

Joined Jan 17, 2008
15
So, when you're taught antenna and wave prorogation theory, why don't they just say that the antenna is emitting photons? I've gotten into arguments with instructors that were die-hard set on the notion that the radiated RF was electrons being transmitted. You'd think this could be spelled out a lot clearer in the curriculum being taught.

#### jonkopp

Joined Jan 17, 2008
15
Another question.

If the wave length of the signal is measured as the completion of one full cycle of alternating states, then why is the measurement made perpendicular to the direction of travel? Wouldn't this be wave width?

For example, the length of a wip antenna determines it's wavelength, but the direction of transmission is most strong perpendicular from the antenna(donut shaped). So for practical purposes you're measuring the wavelength of the signal traveling perpendicular from the antenna, but it's the perpendicular measurement that determines the wavelength.

A better example might be the relationship with the measurement of the Fresnel zone radius for line of site communications. The width of the allowable transmitted path is strongly affected by the wavelength.

What dimension of the wave is being measured here? Are the photons' fields expanding and collapsing, and what we're measuring is more along the lines of a spherical radius alternating is strength? Then why would lower frequencies, with less excitation of the photon, create a larger field than higher frequencies?

#### uzair

Joined Dec 26, 2007
110
Typically when people think about the danger associated with EM radiation they think of the ionising capabilities of the EM radiation, and RF and microwaves are non-ionising. That said RF and microwave can be dangerous to certain parts of the body, for example the eyes, because the heating effect induced by RF or microwaves cannot be dissipated quick enough by the blood flowing from the eyes hence causing (often significant) damage.

Dave
For this matter, a medical guy should also give his opinion!
The radiations of any type (if in excess) can be injurious to health.It is specially dangerous for skin and eyes.It can damage RBC's (Red Blood Cells).In other cells, it usually targets the genetic material, the chromosomes, thus causing changes in it, called mutations.Infact all genetics experiments employ X-Rays for getting "Mutants".

#### scubasteve_911

Joined Dec 27, 2007
1,203
I'm confused, isn't there two models for light? One based upon photon emission and another based upon electromagnetic radiation?

I seem to recall that the two models do not agree, but both are functional.

Steve

#### uzair

Joined Dec 26, 2007
110
Yes there is a wave-particle duality in the case of light.The photons move so fast that they just appear to be a radiation of certain wavelength and energy.de-Broglie's hypothesis explains it

Wavelength= h/mv

#### Dave

Joined Nov 17, 2003
6,970
Yes there is a wave-particle duality in the case of light.The photons move so fast that they just appear to be a radiation of certain wavelength and energy.de-Broglie's hypothesis explains it

Wavelength= h/mv
To quote a chapter I wrote a while back on dielectric heating:

Electromagnetic radiation exhibits both wave properties and particle properties at the same time due to the principle of wave-particle duality. The wave characteristics are more apparent when electromagnetic radiation is measured over relatively large timescales and larger distances, and the particle characteristics are more evident when measuring small timescales on the microscopic level.
For the wave model you need to know:

$$c = f$$$$\lambda$$

And for the particle model you need to know:

$$E = hf$$

c = velocity of propagation in medium (typ. the speed of light if a vacuum)
f = wave frequency
h = Plancks constant
E = Energy in single photon at frequency f

Dave

#### Dave

Joined Nov 17, 2003
6,970
If the wave length of the signal is measured as the completion of one full cycle of alternating states, then why is the measurement made perpendicular to the direction of travel? Wouldn't this be wave width?

For example, the length of a wip antenna determines it's wavelength, but the direction of transmission is most strong perpendicular from the antenna(donut shaped). So for practical purposes you're measuring the wavelength of the signal traveling perpendicular from the antenna, but it's the perpendicular measurement that determines the wavelength.
Can you be a little clearer?

Electromagnetic radiation (EM waves if you like) are defined as transverse, oscillatory, self-propagating wave in space comprised of orthogonal electric and magnetic-field components. Consider a plane wave, if the wave propagates into the z-direction, the E-field is in the x-direction and the H-field is in the y-direction (dependant on perspective). You measure the wavelength in the z-direction and E/H-field magnitudes in the x/y-direction.

Dave

#### thingmaker3

Joined May 16, 2005
5,084
one example which makes clear that photons of different frequency have different energies
is the existence of threshold frequency of wave required for the photoelectric effect.
this effect is one reason IIRC which proved that wave theory alone is not sufficient.
I was reading James Burke just this afternoon... "On the other hand, sometimes light acts as if it were made up of particles. This was first noticed in1873, when a telegraph operator at the transatlantic terminal on the Irish Atlantic coast saw that his equipment was giving off electric current according to the amount of sunlight coming through the window. The more sun, the more current. In the evening no current was present at all. It turned out that the light was hitting selenium metal resistors, so the selenium was obviously giving off electricity in response to light."

Burke then relates German experiments in the 1880's where color of light was shown to have no effect, only the intensity.

Some wild-haired guy named "Albert" proposed that one could count the photons or measure the frequency, but not do both at the same time.

#### Dave

Joined Nov 17, 2003
6,970
Some wild-haired guy named "Albert" proposed that one could count the photons or measure the frequency, but not do both at the same time.
Sounds like Heisenberg, but wasn't that position and velocity.

Dave

#### beenthere

Joined Apr 20, 2004
15,819
I believe that Albert noted that the photoelectric effect was discontinuous, as if individual particles were exciting individual electrons, instead of a smooth effect from even illumination.