Hertz calculating velocity of radio waves (1 Viewer)

[allstarr69]

Hertz was able to calculate the velocity of the waves by reflecting the generated waves off a metal sheet and measuring the wavelength of the standing wave set up by interference.

I dont understand the "standing wave" and intereference bit... can anyone explain exacly how Hertz was able to calculate velocity?

thanks

 

[helper]

Interference is when two waves superimpose.

If two waves superimpose in such a way as their zero points (nodes) are always at the same point the wave will appear to stay still. The centre will vibrate but there will be points that are always zero. This is a standing wave.
Look at a guitar string you will see it. It is what all musical instruments work on.
Same as what Michelson and Morley used, also Bragg.

So by observing the superpositioning, he would know the extra distance the reflected wave had travelled and its wavelength.

 

[Steven12]

I though hertz measured the wavelength by observing the interference pattern by connecting the current loop to the induction coil and place it 45 degrees to the transmitter

 

[mazza_728]

hertz measured the speed of radio waves and showed that, like light, they travelled at c. thus proving maxwell's theories! u dont need to know how he did it.. that is off the course, just know he used standing waves and interference, that is enough! but dont worry about it.. they wont ask you it.

 

[acmilan]

haha now that you said they wont they probably will ask you it.

 

[Shuter]

haha now that you said they wont they probably will ask you it.

I thought he did it something like this:

Reflecting plate 1              [transmitter]
\
 |_______[receiver]
/ \           /
    \        /
      \    /
  ___\/____
 Second Reflecting plate.

So the waves go form the transmitter, and some get reflected directly from the reflector plate 1 strait to the receiver. Others will reflect from reflector plate 1, onto reflector plate 2 and then onto the receiver. By studying the interfearance patterns on the receiver, and knowing the difference in the amount of distance travelled between reflector1-receiver compared to reflector1-reflector2-receiver, it was thus possible to determine what speed the light was travelling at.

 

[helper]

u dont need to know how he did it.. that is off the course

You need to be able to outline his experiment.

I.E. Diagram of setup plus basic steps like Shuter said

 

[CharlieB]

he already knew f from the frequency of the electricity and by working out the wavelength from the interference pattern, he was able to work out c. (c= f x lambda)

 

[allstarr69]

so he wants c. He knows frequency and he works out wavelength by reflecting the electromagnetic waves off a metal sheet at 45 degrees and measuring the standing wave set up by interference.
Is that all they want?


Also does anyone know exacly what Einsteins contribution was to the quantum theory? Im getting alot of different responses to this question...

 

[ashtor]

why is it that in Jacaranda they say that the induciton coil was connected to the reciever with a wire or sumthin?

 

[allstarr69]

i see what you mean lol - "to measure this wavelength, Hertz connected both the trasmittter and the detector loop with a length of wire"

Can someone explain this?

 

[helper]

In Jacaranda they have both methods. The reflection method is on p194

In the wire method, he had current travelling along the wire and radio waves. As these arrive at different times there was an interferance pattern set up, which allowed him to determine the wavelength.

 

[Jase]

Also does anyone know exacly what Einsteins contribution was to the quantum theory? Im getting alot of different responses to this question...

Although Planck had introduced the idea of quantised packets of energy in Black Body radiation, he had none-the-less assumed light to be a wave. Einstein's studies on the photoelectric effect led to the proposal that light is a packet of particles called photons. By observing the energy and frequencies required to remove photoelectrons from a material, Einstein showed that there is a minimum frequency for the effect, and that the energy possesed by each released photon is given by Planck's quanta theory. (E = hf) This led to further discoveries and questionings on the nature of light and particles which is the basis of modern quantum theory.