Question

Question pertaining to Salisbury Screens and Energy Conservation

http://physics.stackexchange.com/questions/65605/salisbury-screens-and-energy-conservation

Answer 1

It appears that the energy "disappear" but the law of conservation of energy states that it can't be destructed. My guess is that the kinetic energy is transformed into potential energy. Or maybe it depends on the context of the waves where do the energy goes?

Answer 2

my first guess would be that the energy is converted to heat, but I don't see how that would happen.

Answer 3

there's no cancellation involved, it just moves it somewhere else. it's a bit misnomer

Answer 4

what do you mean by "it just moves it somewhere else"?

Answer 5

read about Young's double slit experiment

Answer 6

agreed with nin

Answer 7

I don't quite see how the double-slit experiment relates to a salisbury screen, could you explain it?

Answer 8

it gives you a little bit of a background and a way to understanding wave interference

Answer 9

salisbury screens aren't based on diffraction, are they?

Answer 10

I have studied this somewhat, but not extensively, but I don't quite understand how diffraction is involved.

Answer 11

light only gets redirected in an interference. more light shows up in some places and less in other places. think of how compact discs are read

Answer 12

yes, I know what diffraction and interference are. I don't know how diffraction relates to salisbury screens. Salisbury screens shift the phase of half the wave by 1/2 to cancel the wave. I don't see the diffraction there...

Answer 13

here

When the radar wave strikes the front surface of the dielectric, it is split into two waves.
One wave is reflected from the glossy surface screen. The second wave passes into the dielectric layer, is reflected from the metal surface, and passes back out of the dielectric into the air.
The extra distance the second wave travels causes it to be 180° out of phase with the first wave by the time it emerges from the dielectric surface
When the second wave reaches the surface, the two waves combine and cancel each other out due to the phenomenon of interference. Therefore there is no wave energy reflected back to the radar receiver.

there's no crucial difference in diffraction and interference that at least anyone can demonstrate.

Answer 14

so how does diffraction help people understand the problem better than interference?

Answer 15

from the description of a salisbury screen you gave it didn't seem like it was the same as a diffraction grating.

Answer 16

they key in salisbury screen is the interference, but the question was something along the lines of what happens to the energy when it "cancels" out, which I mentioned that there's no real cancelation.

Answer 17

so then the energy is moved where?

Answer 18

else where, if there's another reflector surrounding the whole system we would know.

Answer 19

sorry I don't understand this very well.

Answer 20

that just confused me more.

Answer 21

(shrugs)

Answer 22

because it didn't sound like there are slits on a salisbury screen

Answer 23

so the salisbury screen splits the waves into two parts then has them interfere destructively with each other, the diffraction grating splits the waves into an infinite number of parts and has them interfere both constructively and destructively at different places...
Don't quite see how those two are the same...

Answer 24

but the salisbury screen splits it into only two parts and doesn't change the direction, it just delays the wave. The diffraction grating does change the direction.

Answer 25

or the diffraction after the slits does

Answer 26

also, the amount of space for the wave to diffract is only a quarter of the wavelength, so it almost shouldn't diffract at all

Answer 27

even Feyman says that no one has been able to demonstrate the difference in diffraction and interference.

Answer 28

you've confused me. my brain hurts.

Answer 29

hehehe

Answer 30

I'm glad I'm not studying this kind of physics in college.

Answer 31

so then @AwkwardAvoidnceViking has the next question here - where is the energy moved to? there are no regions of constructive interference...

Answer 32

sounds like a worthwhile experiment. Maybe in college...

Answer 33

or maybe there's something we're not understanding...

Answer 34

it's usually the case for me… :D not understanding anything