EM waves, Light, radio and all that.

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I find EM waves very intriguing. But i get more confused and new questions pop up in my head every time i read something about it. I have a few basic questions.

1. Wavelength: As wavelength is distance between two peaks, how can we measure this distance in cm, meter etc. as physically there are no peaks (Earlier my impression was EM wave is a physical invisible line in air travelling like a sine wave which has the amplitude, wavelength of that given EM wave.)

2. As EM wave is generated when current changes, does this mean all AC current carrying wires in our day-to-day life radiate EM waves?

3. Radio antenna: As current needs to flow to create magnetic fields which generates electric field and hence EM wave. How does it take place in antenna as it does not seem to be closed loop to be able to carry current?

Please try to explain in simplest terms possible. Even though i know definitions of technical terms i fail to relate them to real world phenomena.
So a website link to video or animation would be very helpful to clear my confusion.

Thanks
 

Answers and Replies

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1. An oscilloscope generates a moving spot which moves fast enough to be able to resolve the wave of the electric component after amplification and display an analogy of it on a phosphor. We can then calculate the distance between peaks knowing the frequency and the speed of travel in space.
2. Yes.
3. Nor does the secondary winding of a transformer, yet the voltage is there even if there is no load connected to it. The ratio of voltage to current in an antenna is its characteristic impedance and for best power transfer to its load it has to be matched but whether correctly matched or not a current flows so long as there is a resistive or other loop provided by the load. In transmitting aerials the aerial has to match the impedance of free space for maximum power transfer but even a mismatched aerial will transfer some power into free space.
 

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