# Photoelectric Effect after Passing through Double Slit

1. Jul 14, 2011

### LightNg

Hi,
In a double slit experiment, shooting a photon will produce interference pattern on a screen.

Using a detector to detect which slit the photon passed through will destroy the interference pattern. The photon will pass through only 1 slit, and cause slit pattern on the screen.

The screen detects photon using photoelectric effect, but since the interference is destroyed, is the original frequency of the photon still in tact? I ask this because the photoelectric effect depends on the frequency of the photon.

2. Jul 14, 2011

### fznfire

By the law of conservation of energy, I think the frequency of the photon should be intact.

3. Jul 14, 2011

### ZapperZ

Staff Emeritus
You need to back up a bit and present a very important explanation. Why would the frequency of the photon be affected after it passes through the slits, be it both slits, or just one slit?

Zz.

4. Jul 14, 2011

### LightNg

If the interference pattern disappear, (as in the case of having a detector to detect which slit it pass through), and the photon exhibits particle property now, does the photon still have its frequency intact when it strikes the screen?

5. Jul 14, 2011

### ZapperZ

Staff Emeritus
As I had guessed, you are confusing the light INTENSITY with energy. Just because it "disappears" at a particular point doesn't mean that its frequency has changed!

Zz.

6. Jul 15, 2011

### Drakkith

Staff Emeritus
Hold on. You have misunderstood a key factor here. The interference PATTERN is the result of many photons detected over time. Each photon itself doesn't produce a pattern, only a detection. In the interference pattern, the high amplitude areas are simply areas that we detect the most photons at over time.

7. Jul 18, 2011

### LightNg

This is not about intensity with energy. It is about when the probability wave function collapse, does the frequency of the EM wave still intact? I suppose the answer is yes.

I am not sure if the probability wave has the same frequency as the EM wave, and how 1 affect another.

I know that one. I guess I need to phrase my question better.

8. Jul 18, 2011

### ZapperZ

Staff Emeritus
I have no idea what you just said here. What "collapse" are we talking about that somehow ALTERS the energy/frequency of the photon? In no part of the double slit (i.e. superposition of the PATH that a photon takes through the slit) is there ANY indication of a change in the photon's energy! Yet, you seem to indicate that there is one, especially at the location where the photon underwent a destructive interference. This is puzzling.

Zz.