What is the significance of a wave NOT changing its energy at diffraction?
3d 10h ago by piefed.blahaj.zone/u/akunohana in nostupidquestions from en.wikipedia.org
Diffraction is the deviation of waves from straight-line propagation due to an obstacle or through an aperture, without any change in their energy.
I am trying to read up on and understand diffraction. The example of a water wave under Occurrences was quite easy to understand, especially when contrasted with light waves (image below). However, aren't the water waves losing - and thus changing - their energy as they hit the narrow entrance by losing momentum? As I said, I do understand that the waves diffract from straight lines into curved lines, but the concept of not changing energy is hard to grasp.
What would diffracted light waves look like if they did change their energy at diffraction?
You're talking about perfect categories comparing them with the real world.
Diffraction from objects without the loss of energy doesn't exist, but allows us to solve a simpler equation paving a way to the understanding geometry of the phenomenon.
Real world diffraction is affected by the properties of the material, mostly characterized by linear dielectric permittivity. When you start taking it into account, suddenly the light starts to penetrate into the material, often inducing heat -- the primary source of the losses. Equations become messy, but it kinda allows you to calculate things with high precision.
When a physical wave loses forward momentum, it typically gains amplitude. This conserves the energy of the wave at a lower speed.
Light waves don't really lose speed, so loss of energy would be seen as a lower frequency.
Light waves don't really lose speed, so loss of energy would be seen as a lower frequency.
This is nonsense. To change the frequency, you need highly nonlinear medium (like Raman mechanism in Ethidium bromide) or herald the wave pack, which is not something you probably had in mind.
Hello red shift?
Oh right I forgot to mention another effect that could be observed at high velocities (thousands of km/as for visible light), escaping a gravitational well, or when you expand the space itself. Sorry.
Nonsense? To the contrary, this is the answer to OPs question "What would diffracted light waves look like if they did change their energy at diffraction?" The light waves would change frequency if they lost or gained energy as the amount of energy carried by a photon is directly proportional to it's electromagnetic frequency and is inversely proportional to it's wavelength. So, Photon plus or minus energy equals frequency and wavelength change. Sensible, no?
Nope. Photon energy and the energy of waves are different energies: connected, but not interchangeable.
What would diffracted light waves look like if they did change their energy at diffraction?
I guess the energy loss would be either absorbed into the diffraction medium, or reflected, so it would change colour - or maybe do a cool prism / pink floyd thing?
Sound could go through walls I guess. And there would be no reverberation.