# Wave Interference and Polarization

1. Jun 12, 2013

### jaumzaum

I'm studying wave interference and having trouble to understand some concepts. I would like to ask what would happen in the 2 situations below

Image 1
[Broken]

Image 2
[Broken]

Both waves are identical, have the same frequency, amplitude and velocity. They are polarized on the direction shown (first one oscilates going out of the screen, second one on the plane of the screen). At the red circle they interfere construtively (that means A.Cos(...) are equal). The waves have perpendicular propagation directions. What will be the amplitude on the red points?

I would say 2A for the first image and A √2 for the second. Is it right?

I'm asking because on the slit experiment (OEM interference) my book (and everybody) seems to treat constructive interference as 2A, ignoring the angle between the waves. Why is that?

Last edited by a moderator: May 6, 2017
2. Jun 12, 2013

### Redbelly98

Staff Emeritus
You're correct about the amplitudes. But I would not consider the second example to be constructive interference, I only associate that term if the waves are polarized in the same direction.

Or put another way, try to imagine setting up destructive interference (amplitude is zero) for your plane-polarized example. It can't be done.

Hope that helps.

3. Jun 12, 2013

### jaumzaum

I helps :)

You are right, I used "constructive" because I didn't have other world to use. The amplitude should range from A to A√2, so there will never be a destructive interference.

In the previous post I wrote OEM where I should have written EMW (in portuguese "onda elétromagnética), in english "electromagnetic wave"), sorry for that

Now come the second question. For the second wave we had to consider the angle between them because the wave was oscilating on the plave of the screen. An EMW has 2 fields (electic and magnetic) that are perpendicular to each other, so there will always be a component of one (or both) fields that will be on the plane of the screen. So in the double slit experiment, why they ignore the angle between the waves when they find the phase shift? Is it because the angle is too small?

4. Jun 15, 2013

### Redbelly98

Staff Emeritus
Yes, exactly.

(Sorry about the delay in responding.)