Question

What makes an antenna produce and recieve EM waves (radio waves especially)? what is the property of the antenna , that enables these processes?

Answer 1

Accelerated charged emits an EM wave..

Answer 2

Charges when accelerated produce EM waves..
so basically antenna is just a conductor in which we apply voltage and the accelerate charges at a particular frequency..

does that mean any wire with AC current produces EM waves.. ? YES..
but usually the Ac frequency is TOO low.. (50 or 60hz)
where as for Radio waves u need about 3 khz minimum!

Answer 3

then if the AC is too low,,,what are other alternatives>
?

Answer 4

what you mean?

i just said normally why from wires we don't get EM waves.. cause the ac currents we use is at lower frequency.. not enough to produces radio waves

on the other hand if u want to produce one, all u need is high frequency waves.. and a conductor

Answer 5

ohk!

Answer 6

but ,, while passing AC thru a circuit , the charges are oscillated rite? ,, so it means chrages are accelerated,,,, but accelerated charges MUST emit EM waves,,,,but y doesnt it happen?

Answer 7

even though the frequency is low........

Answer 8

i just told u.. the frequency is TOOO low.. 50hz or 60hz is too low a frequency to produce detectable Em waves!

Answer 9

ohk,,,so theres a fixed lower limit for it to be a EM wave?

Answer 10

u take a string tied to one end..

and then take the other end.. and u move it up and DOWN.. and lets say.. u take one day to move it up.. and one day to move it down

so does that make a wave? no right? :D :D
u need some min frequency ya?

Answer 11

not really... i don't think its that simple.. but its just easy to think it that way :P

Answer 12

then maxwells rule that ALL accelerated charges emit EM eaves isnt true always....?

Answer 13

strictly speaking.. any charge u accelerate at any rate.. it should and will produce EM waves.. but how detectable it is.. and all.. depends on the frequency!

Answer 14

ok,,,,so ina normal AC circuits ,EM waves are produced,,but very faint to be detected ,,,?

Answer 15

so we just neglect it..

but when we talk about AC transmission in power lines and cables, we do consider EM radiation losses .. and they try to minimize it and all!

Answer 16

but in simple ac circuits.. yea its just too weak to detect thats it!

Answer 17

i think a bigggg technical answer is on its way
Saeed must be burning his keyboard.. lets wait for it :D

Answer 18

There is a sender which produces magnetic waves and propagates them in space. It usually happens by electric dipoles - an electron and a proton while oscillating along each other make an electric field and upon which, according to Faraday' law, a magnetic field will be produced and it is then perpendicular to the electric field. a combination of both electric and magnetic fields would produce magnetic waves. An antenna is one in which electrons have the capability of interacting with the received EM waves. It would cause electron to oscillate ....

Answer 19

ok...that is cleared,,,,one more thing,,,,Why is it that ----" TO RADIATE SIGNALS WITH HIGH EFFICIENCY , THE ANTENNAS SHUD HAVE SIZE COMPARABLE TO THE WAVELENGTH OF THE SIGNAL?

Answer 20

well.. to do proper justice to that subject.. u need to understand antennas in detail.. :P..

Answer 21

unless someone can come up with a clever analogy to understand it

Answer 22

its gotta do something with resonance

Answer 23

ok....fine.,,,,i just asked it ,, because in texbook it was mentioned that THIS was one of the reasons why signals are modulated,,,,,bcos u cant make antennas very long

Answer 24

,,What is an example of Ground wave?

Answer 25

mobile phone signals ? radio signals.?