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Physicsissuef
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How does antenna transmits electromagnetic waves? For example radio antenna. How does the antenna produces moving electromagnetic waves?
DaleSpam said:The antenna is a conductor, so charges are free to move inside the antenna. You apply a voltage, charges move, you apply an opposite voltage, charges move the other way.
Physicsissuef said:But what makes them travel?
If I move faster the dipole, will I create bigger frequency? (which is logical, I think so)Troels said:The simple fact that charges in (accelerated) motion *do* radiate electromagnetic waves. Oscilating motion between two ends of a copper wire is such motion.
This is a feature not easily quantified and many textbooks have whole chapters dedicated to describing this effect alone. However I was able to find this wiki-article on a http://en.wikipedia.org/wiki/Dipole_radiation#Dipole_radiation" what mostly cover the important conclusions and features a nice animation of the electric field
Why the electromagnetic waves are partially reflected? When they encounter an interface, I think that there is process called absorption, so the electrons release the excess of energy in form of radiant energy, shouldn't that all energy be reflected?wikipedia said:When encountering an interface, the waves are partially reflected and partially transmitted through.
Physicsissuef said:Why the electromagnetic waves are partially reflected? When they encounter an interface, I think that there is process called absorption, so the electrons release the excess of energy in form of radiant energy, shouldn't that all energy be reflected?
In the sentence it says like, touching no matter what interface, it will partially reflect and partially transmit the waves. So it matter, what is the material of the interface, right?rbj said:if you have a wave traveling along a "string" and somewhere in the middle of that taut string, it changes to 1/4 inch nylon rope (the two are spliced together, then is pulled tight). when the wave is incident upon the splice, some of it will transmit through and some will be reflected.
now replace the 1/4 inch nylon rope with a massive brick wall. here, very little is transmitted and all of it is reflected.
it's because of a change of characteristic impedance of medium.
Physicsissuef said:In the sentence it says like, touching no matter what interface, it will partially reflect and partially transmit the waves. So it matter, what is the material of the interface, right?
I understand, thank you very much.rbj said:the stuff on the other side of the interface has to be different. a different density and/or a different stiffness or compressibility. if you have an interface of some kinda Jello on one side and it's the same Jello on the other side, all of the incident wave will be transmitted.
unnamedplayer said:I'd like to ask a related question. I understand that the transmitter outputs a voltage as a function of time (which creates an electric field) thus causing a flow of charge or current (creating the magnetic field) and these two fields travel down the antenna, but why don't they stop once they reached the end of the antenna. How do they get blasted into space?
Any insight would be greatly appreciated!
Physicsissuef said:How does antenna transmits electromagnetic waves? For example radio antenna. How does the antenna produces moving electromagnetic waves?
unnamedplayer said:I'd like to ask a related question. I understand that the transmitter outputs a voltage as a function of time (which creates an electric field) thus causing a flow of charge or current (creating the magnetic field) and these two fields travel down the antenna, but why don't they stop once they reached the end of the antenna. How do they get blasted into space?
Any insight would be greatly appreciated!
An antenna is made up of conductive materials, such as metal, that are designed to resonate at specific frequencies. When an alternating current is applied to the antenna, it causes the electrons in the conductive material to move back and forth, creating an electromagnetic field around the antenna. This electromagnetic field then radiates outwards as electromagnetic waves.
The frequency at which an antenna resonates is directly related to the wavelength of the electromagnetic waves it transmits. The length and shape of the antenna determine its resonant frequency, which in turn determines the frequency of the electromagnetic waves it emits. Higher frequencies result in shorter wavelengths and vice versa.
Generally, the size of an antenna is directly proportional to the wavelength of the electromagnetic waves it can transmit. This means that larger antennas are capable of transmitting longer wavelengths and therefore lower frequencies, while smaller antennas are better suited for higher frequencies.
Yes, an antenna can transmit multiple frequencies simultaneously. This is achieved by using a technique called frequency multiplexing, where different frequencies are combined and transmitted together. This allows for more efficient use of the electromagnetic spectrum.
Yes, there are several factors that can affect the efficiency of antenna transmission. These include the design and size of the antenna, the material it is made of, the surrounding environment (such as buildings or other obstructions), and interference from other electronic devices. Proper placement and tuning of the antenna can also greatly impact its efficiency.