How does the wavelength of a water wave affect diffraction?

In summary: It was interesting to note that the amount of light passing through the pinhole decreased as you went from a smaller to a wider aperture. This was due to the fact that the smaller aperture allowed more waves to pass through at once. However, the wider aperture allowed more waves to pass through and diffracted more.
  • #1
ranger275
17
0
If I send a single wave toward a corner won't it bend around the corner? If so, how does the wavelength of that single wave (is wavelength defined for a single wave?) effect how much it bends?

Every picture/illustration I have found on diffraction shows a series of lines (plane waves) approaching a gap and shows how the waves bend more if the gap is made smaller. What I haven't seen is a picture keeping the gap the same and changing the wavelength. I don't see how the distance between crests has anything to do with how much each crest bends as it leaves the gap.
 
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  • #2
What do you mean by a single wave? do you mean a single crest? If so than you have to understand that short wave packets such as your single crest wave can be Fourier expanded into a sum of multiple crest waves (Principle of superposition). Each component of that expansion will diffract according with its wavelength.
 
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  • #3
ranger275 said:
I don't see how the distance between crests has anything to do with how much each crest bends as it leaves the gap.

Interesting that it does, isn't it?
 
  • #4
ranger275 said:
If I send a single wave toward a corner won't it bend around the corner? If so, how does the wavelength of that single wave (is wavelength defined for a single wave?) effect how much it bends?

Every picture/illustration I have found on diffraction shows a series of lines (plane waves) approaching a gap and shows how the waves bend more if the gap is made smaller. What I haven't seen is a picture keeping the gap the same and changing the wavelength. I don't see how the distance between crests has anything to do with how much each crest bends as it leaves the gap.

What is the difference? If the geometry is described in units of 'a wavelength', the absolute size of things is not relevant. The scale of the picture that's drawn may alter but the angles don't, for a given ratio of gap to wavelength.
 
  • #5
ranger275 said:
What I haven't seen is a picture keeping the gap the same and changing the wavelength.

Here you go. This video shows changing the wavelength of a water wave through an aperture.

 
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  • #6
Drakkith said:
Here you go. This video shows changing the wavelength of a water wave through an aperture.



Great video! (Although some of the comments below it appear to be wrong.)
 
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  • #7
olivermsun said:
Great video! (Although some of the comments below it appear to be wrong.)

It's youtube. I'd be surprised if you didn't find a reference to hitler or nazis in the comments.
 
  • #8
One point that's easy to forget. If you go from a narrow to a wide aperture, for the same wavelength, you get more total energy passing through. The actual amount of energy flowing 'off axis' may not change significantly. It's just that more energy gets through and that energy goes in the forward direction.
You get very little light through a pinhole, compared with a porthole but the porthole is still diffracting some. The diffraction at the edges can be very relevant even when an object is very large. It must, for instance, be a consideration for Stealth designs, where they go to a lot of trouble to make sure that specular reflections are angled away from the horizontal - yet there will be some energy reflected (due to diffraction) right back at the transmitter, unless they eliminate / reduce it in some way.
 
  • #9
Thank you for all the comments. The video did clearly show the change in refraction as you changed wavelength.
 

1. What is diffraction?

Diffraction is the bending of waves around obstacles or through small openings. It occurs when a wave encounters an obstacle or an opening that is comparable in size to its wavelength.

2. How does the wavelength of a water wave affect diffraction?

The wavelength of a water wave is directly proportional to the amount of diffraction. This means that as the wavelength increases, the amount of diffraction also increases. This is because longer wavelengths have more energy and are able to bend around obstacles more easily.

3. What is the relationship between the size of the obstacle and the amount of diffraction?

The size of the obstacle is inversely proportional to the amount of diffraction. This means that as the size of the obstacle increases, the amount of diffraction decreases. This is because larger obstacles are able to block or absorb more of the wave's energy, resulting in less bending.

4. How does the amount of diffraction change with different types of water waves?

The amount of diffraction depends on the type of water wave. For example, ocean waves have longer wavelengths compared to ripples on a pond, so they will diffract more around obstacles. Additionally, the shape and depth of the water can also affect the amount of diffraction.

5. Can the wavelength of a water wave be controlled for diffraction experiments?

Yes, the wavelength of a water wave can be controlled in experiments by adjusting the source of the wave, such as the frequency of a wave generator. By changing the frequency, the wavelength of the water wave can be altered, resulting in varying amounts of diffraction.

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