antennas (and communication via gravity)

[biggs]

hi

i have a question about antennas (and an unrelated question about gravity)

 

Question 1

does the length of an antenna have to take into account the amplitude? (ive no idea what the amplitude of a standard broadcast radio wave is) if the antenna was smaller than the amplitude, it would not be able to pick up the entire wave, so information would not be recieved, is this right?

so if an emp from say a nuke went off, would all electronic devices within range break, or only those with a conductor in the circuit long enough to recieve the full magnitude of the amplitude of the emp?

 

Question 2

anyway, second unrelated question. err after i read http://www.scienceforums.net/forums/showthread.php?t=14262 , i thought of an idea but it's dependant if gravity has a speed or not... so does it? the posts dont really seem to answer anything and some contradict each other. by speed, i mean the effect gravity has on nearby mass, so for example

 

if our sun, for no apparent reason exploded into a ultra mega super nova and all of the mass was turned into energy, it would take around 8 minutes for us on earth to realise we're about to be burnt to oblivion, but before the rather intense light reaches us, will earth continue to orbit around the virtual sun? or would we wander off in a tangent since the sun is no more...... ?

 

the idea that the earth would continue to orbit nothing doesnt seem very logical to me but that fact that gravity is instantaneous doesnt seem very logical to me either ..... because

 

if it was, then wouldnt we be able to communicate faster than the speed of light through gravity? for example, lets say there are two celestial masses and they are 10 light minutes away. Each, relative to each other, are not moving. if i was to move one over a bit, the gravity change would be noticed on the other, before the light from the first reached the second to tell that the planet had moved. instant communication??

[biggs]

hmm, after a bit of thinking, i realised that if you were to move a celestial body over a bit, you'd have to eject a fair bit of matter out the other way, which would probably negate the displacement of gravity.

if this is the case, then instead of moving, lets use the matter turns into energy idea, so i have a giant machine that turns planets into energy, then back into planets ... you could get a bit of binary digits through

[Klaynos]

Question 1: it has to be around n wavelengths to get a good reception from a perticular broad cast I belive, it might be n/2 wavelenths though... I think in most cases they attempt to set up a standing wave along the arial...

 

As for the EMP effect I'm unsure.

 

Question 2: if the sun vanished in an instant the earth would continue to orbit it for around 8 mins, the effective release from it's orbit would happen at the same time we see the sun disappear...

[mmalluck]

Question 1:

 

The length of an antenna has everything to do with the wavelength it recieves and nothing to do with the amplitude of that wave.

 

EMPs play on the fact that any piece of metal can be considered an antenna. The most hazardus to silicon semiconductors are the metal traces on the circuit boards themselves. Each copper trace can be seen as an antenna and given the right frequency create a voltage potential. Silicon doesn't like excessivly high voltages and often fuses., destroying the circuit. The trick is getting the right frequency of radio energy.

 

Nuclear weapons make massive radio burst when detonated in the upper atmosphere. These radio burst cover a large range of radio frequenies and make them an effective emp device.

 

Question 2: Gravity affect move at the speed of light.

[GeminiinimeG]

Wait a minute. LEts just say this guys are right. If the sun exploded, and gravity would leave us at the same time that we saw the sun destroyed, wouldnt we be stuck permenently looking at the same image because wed be going away from the blast, or at least time would seem to slows down to us?

[insane_alien]

no gemini no we wouldn't. light always goes at c relative to the observer no matterhow fast you go.

[GeminiinimeG]

So its all relative =D meaning different places in universe perceive things differently, quite scary aint it

[insane_alien]

nope not scary at all.