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Hertz's Experiments (1 Viewer)

1729

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How did Hertz measure the speed of radio waves? Different sources say different things however they all said the frequency of the wave was known due to the experimental setup:

1. He allowed radio waves to reach the receiver via two different paths: one direct and one after reflecting off a metallic surface. This produced an interference pattern near the receiver which was studied to find wavelength.

2. He reflected the radio waves with 90 degree incidence angle off a flat plate to produce a standing wave and then he moved the receiver along the wave and calculated half the wavelength as the distance between nodes or antinodes.

3. He used diffraction to produce a resulting waveform which was studied to find wavelength.

Which of these is correct? Why are there so many different versions?
 

sida1049

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Experimental setups (1) and (2) are equivalent. They're describing the same thing but with slightly different words.

I'm not sure about (3); I can't verify it online, and it sounds incorrect.
 

1729

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Experimental setups (1) and (2) are equivalent. They're describing the same thing but with slightly different words.

I'm not sure about (3); I can't verify it online, and it sounds incorrect.
How are 1 and 2 equivalent?

1: speed-of-radio-waves.png

2: 006e.gif

Also, does (1) produce a standing wave? Don't you need two waves of the same frequency interfering while travelling in opposite directions?
 

sida1049

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How are 1 and 2 equivalent?

1: View attachment 34532

2: View attachment 34531

Also, does (1) produce a standing wave? Don't you need two waves of the same frequency interfering while travelling in opposite directions?
Ahh, I see the problem now; I visualised (2) as (1). When I did HSC physics, I was taught that Hertz's experimental setup was (1). And you're absolutely right; you do need two waves travelling in opposite directions to generate a standing wave.

It's entirely possible that (1) and (2) are experimental setups that Hertz constructed at some point, but I haven't dug far enough to check whether he actually did. I would recommend going with (1) to be safe.
 

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