# Two slit experiment at home and interference

1. Nov 21, 2014

### jimmylegss

Why is it possible to do this experiment at home and still see light as a wave? Isn't there loads of interference? Or does this have to do with wavelength? If you use a laserpen and 3 needles you can basicly do it at home without shielding off anything...

2. Nov 21, 2014

### ShayanJ

The reason is that those neat interference patterns can't be seen using any kind of light. The condition for interference to happen is that the two waves being interfered should be coherent. All of those other lights in the room don't satisfy this and so can't interfere in some way that disturbs your experiment. But two waves coming from a single point source, are indeed coherent. For extended sources, the source should be of special kind, which a laser is!

3. Nov 21, 2014

### jimmylegss

Im sorry, I did not phrase that very well.

I mean how can I observe and disturb that pattern? Since you can easily do this outside a vaccuum? Basicly I got a laser, shine it through 2 slits, and it shows a wave pattern. But how can i interfere and disturb that wave pattern and make them go through either one of the slits (and not see the wave pattern on the other side, just two blots of light).

4. Nov 21, 2014

### Staff: Mentor

You can't do that easily at home. The challenge is that you need detectors that will produce the necessary which-path information without absorbing the light (or you'll get no spot at all). Google around and you'll find some writeups of how it can be done with the resources of a (better than average) college physics lab.

5. Nov 21, 2014

### Staff: Mentor

Mount the slits firmly, then very carefully move a sharp edge like a razor blade behind them, so it blocks one of the slits.

6. Nov 21, 2014

### jimmylegss

haha no i meant interfering with the wave pattern before it hits the screen with both slits open.

7. Nov 21, 2014

### Staff: Mentor

8. Nov 21, 2014

### StevieTNZ

Last edited: Nov 21, 2014