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Author Topic: Radioactive Microwaves?!?!  (Read 6800 times)

Offline stana

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Radioactive Microwaves?!?!
« on: 25/11/2007 15:49:26 »
Hey me and a freind were talking about sat navs..and he said that radioactive beams were used to get information from space into my sat nav system

He also said micro waves use radation to cook my food

and that televisions use radiation to show me my chanels

Is this true!?

If it is, if i use my sat nav or microwave every day, does this mean the amount of radiation over a period of time will kill me?


 

another_someone

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Radioactive Microwaves?!?!
« Reply #1 on: 25/11/2007 16:08:55 »
Radioactive and radiation are two different things.  Something that is radioactive is a thing that emits radiation, it is not the radiation itself (more commonly, it is considered radioactive if it emits nuclear radiation, although technically you could argue that a light bulb is radioactive since it emits light radiation).

Radiation is a very broad term (technically one might say that to talk about a beam of radiation is an oxymoron, but it is now a commonly used term and has taken on meaning).

Technically, radiation is the act of radiating from a source, that is, to spread out from a source (this use is still used in biology, when a species may radiate into new habitats).

In physics, radiation usually refers to the transmission of energy over a distance (originally, I assume it referred to the radiating of energy, i.e. the spreading out of energy - hence my reference to a beam of radiation being an oxymoron).  The form and nature of that energy can be very wide, and so the effects of that energy can be very varied.  The energy can be harmful in nature, or it can be totally harmless in nature, but it still amounts to radiation.

Radio waves, beta radiation (which are electrons), alpha radiation (which are helium nuclei), light, X-rays, and even sound, are all forms of radiation.

Theoretically, too much of any radiation will harm you - you can be killed by too much sound energy, but that does not mean you should lock yourself in a sound proof box to protect yourself from the harmful effects of too much sound.
 

Offline techmind

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Radioactive Microwaves?!?!
« Reply #2 on: 26/11/2007 14:06:51 »
Hey me and a freind were talking about sat navs..and he said that radioactive beams were used to get information from space into my sat nav system

He also said micro waves use radation to cook my food

and that televisions use radiation to show me my chanels

Is this true!?

If it is, if i use my sat nav or microwave every day, does this mean the amount of radiation over a period of time will kill me?
As another_someone has already said, "radiation" is something of a catch-all term and is not especially useful.
For practical discussions (within science) we sub-divide into:-
- "ionising radiation" (which is conventional "radioactive" (nuclear) radiation; alpha, beta, gamma, plus X-rays) which can cause cell-damage even at low intensities. Damage due to ionising radiation is significantly cumulative - limits are set on total dose over given period (hours, days, years).
- "non-ionising radiation" is radiowaves, microwaves, infra-red, visible, ultraviolet - and is primarily only harmful if too intense, causing physical heating of the body. There is no cumulative effect to non-ionising radiation - the health limits are based purely on the likely heating effects during the exposure itself. It's a bit like saying that if you put your hand in boiling water you'll cause immediate damage, but if instead you kept your hand in warm water all day it wouldn't harm.

Sat-nav uses microwave signals at a few GHz. The signals are transmitted towards the earth and received by the handheld GPS unit. The signals are incredibly weak. The handheld unit doesn't transmit (emit) anything. Not harmful. I don't know what the satellite transmitter power is, but we're looking at something like 50watts spread over the entire earths' disc (they're not "beamed" to any specific GPS receiver).
(By comparison, the sun's visible and infra-red radiation amounts to almost 1000W per square metre of the earth's surface.)

A microwave oven (usually at 2.45GHz) uses similar frequencies to sat-nav, but pumps 600-800Watts of energy into a small box. A small amount of microwave energy leaks from the edges of the door seal, but not much.

A handheld mobile telephone transmits at 900MHz or 1800MHz (0.9 or 1.8GHz) and is one of the stronger sources of radiowaves (non-ionising radiation) you are likely to encounter in everyday life. Even at full power (which it will rarely use) a phone only emits around 0.25W of radio energy - which is less than a torch-bulb puts out in visible and infra-red light.

Terrestrial (conventional) television transmitters emit radiowaves at 470-850MHz (0.47-0.85GHz). Depending on the area, it'll be from a 50W transmitter for a local town repeater to 50000W for a big regional transmitter. But when you're a sensible distance away the power is still spread out so thinly that it's not harmful. They would not allow an engineer to work on the tower close to the transmitting aerial itself while it was operating however.


« Last Edit: 26/11/2007 14:29:09 by techmind »
 

lyner

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Radioactive Microwaves?!?!
« Reply #3 on: 26/11/2007 15:36:01 »
The biggest helping of 'radiation' you get, on a daily basis, is from the good old Sun. 'Full on' to your body at mid day you are getting at least 0.5kW, altogether. Most of it is around the visible region and infra red but there's a whole range of frequencies.  And it's all free. Where would we be without it?
 

Offline Pumblechook

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Radioactive Microwaves?!?!
« Reply #4 on: 07/12/2007 22:51:51 »
I am worried that the electricity coming into our house is radioactive coz some of it comes from nuclear stations.
 

lyner

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Radioactive Microwaves?!?!
« Reply #5 on: 07/12/2007 23:00:31 »
electricity doesn't care where it came from. It's a bit like money, that way.
 

Offline techmind

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Radioactive Microwaves?!?!
« Reply #6 on: 07/12/2007 23:04:46 »
I am worried that the electricity coming into our house is radioactive coz some of it comes from nuclear stations.
I hope you're leg-pulling...?  ;)

It is not physically possible for electricity (electrons) to be radioactive. Radioactivity comes from decaying atomic nuclei; since electrons are not nuclei they cannot undergo that sort of decay.

In any case, the particular electrons in your wires in your home can never travel further than a local loop of a mile or so from your home... there is a closed circuit from your house (and all the neighbours') to the local substation, through the windings of the transformer, and back through the other wire to your house. The AC current just oscillates back and forth in the wire. The energy from the power station is coupled into your local wiring via magnetic coupling in the sub-station transformer. There is no continuous wire from your house to any power station.

I leave it as a exercise for someone else to work out whether the electrons even get as far as the substation in each 50Hz cycle.  ::)
« Last Edit: 07/12/2007 23:07:35 by techmind »
 

Offline Pumblechook

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Radioactive Microwaves?!?!
« Reply #7 on: 08/12/2007 10:30:48 »
It was a wind-up.

I don't think individual electrons travel very far at all.  They are continually leaving and re-joining atoms in the conductor. 
 

lyner

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Radioactive Microwaves?!?!
« Reply #8 on: 08/12/2007 10:55:07 »
The drift velocity of conduction electrons is only a few mm per second!
 

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Radioactive Microwaves?!?!
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