Why magnetic feilds are not dangerous for health but ELCTROMAgnetic fields are

[Arslan]

Why magnetic fields from magnet r slenoid are not dangerous but if we have an antenna radiating elctromagnetic fields is dangerous?

 

[Studiot]

The electromagnetic fields radiating from an antenna are alternating fields.

The magnetic field emanating from a solenoid is static.

To present a danger the field has to interact either with the atoms of your body or an attached piece of metal (eg a ring). (other than as a straight forward magnet) Only alternating fields can do this. Furthermore the interaction depends upon the frequency of the field alternation, some some frequencies are more dangerous than others.

This is not to say that an extreme static field might not present a danger, but normally encountered ones are OK.

 

[ZapperZ]

Why magnetic fields from magnet r slenoid are not dangerous but if we have an antenna radiating elctromagnetic fields is dangerous?

Where do you get the idea that the latter is dangerous?

Zz.

 

[dabi]

A static magnetic field does not transport any energy, whereas electromagnetic fields do.
The danger comes from the absorption of this energy by molecules which get destroyed,
think of UV-radiation and skin cancer.

 

[ZapperZ]

A static magnetic field does not transport any energy, whereas electromagnetic fields do.
The danger comes from the absorption of this energy by molecules which get destroyed,
think of UV-radiation and skin cancer.

Where does one encounter a "UV" antenna?

Zz.

 

[dabi]

Where does one encounter a "UV" antenna?

Zz.

This was an example of electromagnatic fields, that are really harmful.
The energy emitted by antennas is much to weak to give any direct
indication for health threats.

 

[ZapperZ]

This was an example of electromagnatic fields, that are really harmful.
The energy emitted by antennas is much to weak to give any direct
indication for health threats.
[PLAIN]http://xa.ly/gGd[/QUOTE]

You do remember the original question, don't you?

Why magnetic fields from magnet r slenoid are not dangerous but if we have an antenna radiating elctromagnetic fields is dangerous?

Zz.

 

[Arslan]

Where do you get the idea that the latter is dangerous?

Zz.

They are really dangerous. Microwave Consists of waveguide that radiate microwaves into oven and cock food too.

 

[ZapperZ]

They are really dangerous. Microwave Consists of waveguide that radiate microwaves into oven and cock food too.

Then why aren't you getting cooked now? After all, there are microwaves around you.

Zz.

 

[sophiecentaur]

Isn't it just a matter of how much power is in the em fields?
If non-ionising em fields were harmless, whatever, then there would be no records of people getting fried in front of transmitting antennae and there would be no health and safety problems. The legal exposure limits are there for a reason.

 

[NobodySpecial]

Where do you get the idea that the latter is dangerous?

From the big warning notices, the fence and the number of lockouts and sign-offs I have to get before I climb upto the feed horn.

The poster didn't say that RF antennea around them are dangerous, they just asked why you don't want to put your head inside a KW radar but you can put your head inside a 4T MRI

 

[ZapperZ]

From the big warning notices, the fence and the number of lockouts and sign-offs I have to get before I climb upto the feed horn.

Are you sure those notices are not predominantly for high voltage?

The poster didn't say that RF antennea around them are dangerous, they just asked why you don't want to put your head inside a KW radar but you can put your head inside a 4T MRI

You got all that from "... an antenna radiating elctromagnetic fields is dangerous..."? I could also interpret it as being 1 mile away from a radio transmitter. Where is the danger there?

The original premise is VERY vague. It is why I asked for the OP to clarify how he/she concluded that something is "dangerous". You made way too many assumption of what he/she meant.

Zz.

 

[NobodySpecial]

Are you sure those notices are not predominantly for high voltage?

That and the risks of the incredibly weak gravity field when I'm 30m up in the air ;-)

I know there is a natural reaction against Wifi/cellphone is killing our children type hysteria - but there is a valid question.
There are books full of legislated safe field limits for all kinds of RF transmitters across orders of magnitudes in frequency yet I've never seen anything more than occasional research papers on the effects of extreme magnetic fields.
That and the odd anecdote of chemists who got headaches while looking into NMRs

But the answer from studiot is partly correct, that only if you move in a B field do you get an induced current, although there are enough moving charges in a body that you would think there would be some chemical effect

 

[Studiot]

There are also indirect means whereby both magnetic and electromagentic fields can be dangerous, if they are alternating.

A colleague once lost a finger, cooked by induction in his ring, from a radar beam.

 

[ZapperZ]

And I think people here are beginning to express the point that I had in mind in the very beginning, but was hoping that the OP him/herself would be the one who gets it.

To claim that something is "dangerous" requires an analysis of how "strong" something is, and at what frequency. An "antenna" emitting EM signal is not automatically dangerous. To agree with the original post and go right into explaining why it is so is highly irresponsible, because it automatically validates such a faulty claim.

Zz.

 

[mrspeedybob]

I think it's a matter of intensity for both magnetic and electromagnetic fields.

The body makes a lousy antenna, but given a strong enough em field even a lousy antenna will be enough to collect a dangerous amount of energy. The strength of alternating field needed to cause harm will be different depending on the frequency and on the details of the particular person exposed, but I would bet that any frequency at sufficient amplitude would be hazardous.

Concerning static magnetic fields, I have no trouble imagining a field so strong that your blood moving through it would have sufficient current induced to undergo electrolysis. Vapor in your blood stream is not a good thing.

So basically there is no difference. They can both be harmful in sufficient quantities. For that matter almost anything can be harmful into large a quantity. Water, oxygen, exercise, sex, you name it...

 

[Studiot]

An "antenna" emitting EM signal is not automatically dangerous.

I'm sorry, but I have to respectfully disagree with you.

Anything capable of causing significant physical harm to a human can be classified as dangerous.

It is not necessary for it to ever have done so, just that it possesses the capability. Many things in our lives and environment are thus dangerous. Life is full of danger. That is why we all have to learn how to avoid or control the danger.

 

[arydberg]

I once heard of a guy who got exposed to a radar beam. He complained about feeling tired, sat down and died. The autopsy said his insides were cooked. I think the exposure limits are set by how much heat is produced by the beam.

 

[ZapperZ]

I'm sorry, but I have to respectfully disagree with you.

Anything capable of causing significant physical harm to a human can be classified as dangerous.

It is not necessary for it to ever have done so, just that it possesses the capability. Many things in our lives and environment are thus dangerous. Life is full of danger. That is why we all have to learn how to avoid or control the danger.

Then you're saying that a flashlight emitting light is a "dangerous" source of EM radiation.

Zz.

 

[Studiot]

Then you're saying that a flashlight emitting light is a "dangerous" source of EM radiation.

In principle, yes. If you shine it directly into a driver's eyes, you could temporarily blind him and cause a fatal accident.

The test is, 'Is is capable of...?'

not

'Is it likely that..?' or 'Would it be stupid or a misuse...?'

 

[ZapperZ]

In principle, yes. If you shine it directly into a driver's eyes, you could temporarily blind him and cause a fatal accident.

But this isn't the criteria of what the OP wants, is it? It is the same irrelevant fact that these things have high voltage sources. Is that what the OP is really using as a criteria for being "dangerous"?

This thread has gone off the deep end. Rather than take this opportunity to EDUCATE someone to think of what one considers to be "dangerous", and why, it has turned into "let's go to the ridiculous extent of labeling everything as being dangerous and be done with that". This is no longer physics. It should be posted in the psychology forum (if we have one), because we can't treat paranoia here.

Zz.

 

[sophiecentaur]

I agree - this has got out of hand.
There are two known harmful effects of em radiation, with high enough exposure. One is ionisation - which produces damage to the DNA and the other is heating - which can damage tissue, once the temperature is high enough to affect the enzymes in cells.
You need sufficiently high levels of exposure for any significant harm to occur, just as you need to fall from a great enough height to damage yourself.
If the frequency involved is low enough - or zero, the effects seems to be much much less, for a given value of field.

 

[Arslan]

what about transformers, Are dangerous for health...they have varying magnetic fields

 

[sophiecentaur]

And where does the biggest field occur? Do you ever sit in the middle of a transformer?

 

[Arslan]

220Vrms is enough to induce 2Vrms or 3Vrms upto 15 meter. And step down transformers have much higher voltages than 220Vrms.

But i think transformers have magnetic fields only

 

[sophiecentaur]

Induce 2V into what? You would need to specify the field in V/m (or probably in T - which would require to know the current through the transformer) and the size of the 'receiving' structure. Also, the impedance of the measuring device would be relevant.

You say transformers have magnetic fields only. That's true in practical terms because the radiation resistance of an object much less than 1m across is vanishingly small at the wavelength associated with 50Hz. The E field is, of course, very small.

btw, I have no feelings either way about the health hazards of low (mains) frequency fields. Their effects fall into the same categories as the health issues associated with organic foods and the effectiveness of Homeopathy; I am not aware of much hard evidence to support the 'crank' (nuthin personal, guv, you understand) views about any of them.