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The Electromagnetic Spectrum





designervibe02
Quote:
You actually know more about it than you may think! The electromagnetic (EM) spectrum is just a name that scientists give a bunch of types of radiation when they want to talk about them as a group. Radiation is energy that travels and spreads out as it goes-- visible light that comes from a lamp in your house and radio waves that come from a radio station are two types of electromagnetic radiation. Other examples of EM radiation are microwaves, infrared and ultraviolet light, X-rays and gamma-rays. Hotter, more energetic objects and events create higher energy radiation than cool objects. Only extremely hot objects or particles moving at very high velocities can create high-energy radiation like X-rays and gamma-rays.

Here are the different types of radiation in the EM spectrum, in order from lowest energy to highest:

Radio

Radio: Yes, this is the same kind of energy that radio stations emit into the air for your boom box to capture and turn into your favorite Mozart, Madonna, or Justin Timberlake tunes. But radio waves are also emitted by other things ... such as stars and gases in space. You may not be able to dance to what these objects emit, but you can use it to learn what they are made of.

Microwave

Microwaves: They will cook your popcorn in just a few minutes! Microwaves in space are used by astronomers to learn about the structure of nearby galaxies, and our own Milky Way!

Infrared to UV

Infrared: Our skin emits infrared light, which is why we can be seen in the dark by someone using night vision goggles. In space, IR light maps the dust between stars.

Visible: Yes, this is the part that our eyes see. Visible radiation is emitted by everything from fireflies to light bulbs to stars ... also by fast-moving particles hitting other particles.

Ultraviolet: We know that the Sun is a source of ultraviolet (or UV) radiation, because it is the UV rays that cause our skin to burn! Stars and other "hot" objects in space emit UV radiation.

X-ray

X-rays: Your doctor uses them to look at your bones and your dentist to look at your teeth. Hot gases in the Universe also emit X-rays .

Gamma-ray

Gamma-rays: Radioactive materials (some natural and others made by man in things like nuclear power plants) can emit gamma-rays. Big particle accelerators that scientists use to help them understand what matter is made of can sometimes generate gamma-rays. But the biggest gamma-ray generator of all is the Universe! It makes gamma radiation in all kinds of ways.
ocalhoun
designervibe02 wrote:

Microwave

Microwaves: They will cook your popcorn in just a few minutes! Microwaves in space are used by astronomers to learn about the structure of nearby galaxies, and our own Milky Way!

Microwave frequencies are also often used for wireless communications between distant points... including between the Earth and various satellites.
Also, most radars use various microwave frequencies.

You could have saved a lot of trouble and just posted something like this though:
Dennise
But is the beginning of the radio wave part of the EM spectrum (i.e. the low frequencies/long wavelengths) really arbitrary? Is there some 'magic' low frequency at which EM waves produce what is sometimes called "action at a distance"? Probably not.

Instead, the defined beginning of the radio waves part of the EM spectrum is likely simply a practical matter based on antenna lengths in this part on the spectrum.

Anybody know?
ocalhoun
The beginning of the EM spectrum is 0hz... (DC, or stationary magnetic field)

And the next step would be 0.0000{infinite number of 0's}0001hz... There's no theoretical reason why you couldn't have a electromagnetic signal that oscillates every (say) 4 trillion years.

The usable EM spectrum is limited by our technology. Our oscillators and RF components are limited in the frequencies they can handle. (By size, by power requirements, and by temperature tolerance.)

There may be an upper limit to the frequencies as well; eventually, the wavelength might become too small to exist... I'll leave that to the quantum physics experts to decide.
Bikerman
There are also more practical considerations.
Low frequency=long distance (as a general rule). Hence LW radio has a much greater range than MW or SW. Very energetic (high frequency) radiation is quickly absorbed - which is why you can shield a microwave oven pretty easily.
ocalhoun
Bikerman wrote:

Low frequency=long distance (as a general rule). Hence LW radio has a much greater range than MW or SW. Very energetic (high frequency) radiation is quickly absorbed - which is why you can shield a microwave oven pretty easily.

... In a vacuum, high-frequency and low-frequency signals of the same power should have about equal range... (Though not equal data-carrying capacity.)

Low frequency is better at penetrating objects in the way though, so it does give longer range when there's stuff in the way.
Bikerman
We were talking about radio. There is ALWAYS something in the way. Even air can absorb the higher frequencies - particularly if it is humid.
ocalhoun
Bikerman wrote:
There is ALWAYS something in the way.

(except in communications between spacecraft)
Bikerman
ocalhoun wrote:
Bikerman wrote:
There is ALWAYS something in the way.

(except in communications between spacecraft)
Even then. Local space is full of junk, and solar-system space has quite a lot of 'stuff' (mainly gasses) in it. Our spacecraft (with the exception of the Voyager craft) operate in pretty low orbit and there is still a significant amount of 'stuff' around. Of course any attenuation of the signal is bound to be MUCH less.
chatrack
Hi,
I some books, EM spectrum starts in AC waves. Wonder why our
technology can not receive LW EM. I think we need to break the
conventional mehods of LC tank circuits or PLL methods.
Bikerman
chatrack wrote:
Hi,
I some books, EM spectrum starts in AC waves.
Get a better textbook then.
Quote:
Wonder why our technology can not receive LW EM.
Ever heard of long-wave radio?
Quote:
I think we need to break the conventional mehods of LC tank circuits or PLL methods.
I don't understand what you are saying. Why should we 'break' phase locked circuits and what does that even mean?
saratdear
Quote:

Infrared: Our skin emits infrared light, which is why we can be seen in the dark by someone using night vision goggles.

Can anybody confirm this? This was news to me!
Bikerman
EVERYTHING emits radiation. The temperature of the 'thing' determines what wavelength of radiation is emitted - the hotter something is, the shorter the wavelength of the emitted radiation.


We typically radiate about 1000 Watts of energy continuously. Normally the surroundings radiate about 900 Watts back at us, so we only have to burn food to make up the extra 100 Watts.
Because of our temperature, the radiation emitted is in the infra-red, so the quote is quite correct.
taytay
designervibe02 wrote:

Visible: Yes, this is the part that our eyes see. Visible radiation is emitted by everything from fireflies to light bulbs to stars ... also by fast-moving particles hitting other particles.


Light is also used for digital communication. I.e., Fiber Optics. and FioS! I wish I had fios Sad My internet is so dang slow here, meanwhile the neighborhood next to me has fios! evil verizon.
Bikerman
taytay wrote:
designervibe02 wrote:

Visible: Yes, this is the part that our eyes see. Visible radiation is emitted by everything from fireflies to light bulbs to stars ... also by fast-moving particles hitting other particles.


Light is also used for digital communication. I.e., Fiber Optics. and FioS! I wish I had fios Sad My internet is so dang slow here, meanwhile the neighborhood next to me has fios! evil verizon.

That is unlikely to be a result of the cable alone. 2MB plus is a pretty reasonable speed, unless you are doing a lot of very large data transfers, and that is easily possible over copper wire. It depends on things like your distance from the local telephone exchange (the greater the distance the slower the speed has to be), the number of people sharing the same connection (called the 'contention' rate), and the willingness of the telco to put new equipment in place.
saratdear
Bikerman wrote:

We typically radiate about 1000 Watts of energy continuously. Normally the surroundings radiate about 900 Watts back at us, so we only have to burn food to make up the extra 100 Watts.
Because of our temperature, the radiation emitted is in the infra-red, so the quote is quite correct.

Thank you for the explanation. And now for an absurd question - is it possible to harvest the power our body is emitting?
Bikerman
saratdear wrote:
Bikerman wrote:

We typically radiate about 1000 Watts of energy continuously. Normally the surroundings radiate about 900 Watts back at us, so we only have to burn food to make up the extra 100 Watts.
Because of our temperature, the radiation emitted is in the infra-red, so the quote is quite correct.

Thank you for the explanation. And now for an absurd question - is it possible to harvest the power our body is emitting?

Yes - watch the matix Smile
No, seriously, it isn't really practical. You have to put energy in (food) to get energy out (heat) and it is a terribly inefficient way of converting one type of energy into another..You would be better to run an old inefficient electric heater Smile
saratdear
Bikerman wrote:
saratdear wrote:
Bikerman wrote:

We typically radiate about 1000 Watts of energy continuously. Normally the surroundings radiate about 900 Watts back at us, so we only have to burn food to make up the extra 100 Watts.
Because of our temperature, the radiation emitted is in the infra-red, so the quote is quite correct.

Thank you for the explanation. And now for an absurd question - is it possible to harvest the power our body is emitting?

Yes - watch the matix Smile
No, seriously, it isn't really practical. You have to put energy in (food) to get energy out (heat) and it is a terribly inefficient way of converting one type of energy into another..You would be better to run an old inefficient electric heater Smile

Somehow, I never got a chance to watch that movie. Smile
Thanks for the explanation anyway.
ocalhoun
Bikerman wrote:

Yes - watch the matix Smile
No, seriously, it isn't really practical. You have to put energy in (food) to get energy out (heat) and it is a terribly inefficient way of converting one type of energy into another..You would be better to run an old inefficient electric heater Smile

... Or for performing the same energy transformation (chemical to heat), burn the food.

/heartily agree about the flawed science of the matrix
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