Diffraction and Conservation Principle

[netrat]

CASE:-

In single slit experiment light from a source diffracts forming light and dark bands.

 

Question:-

Energy of light(from source) = sum of energies in all light bands ?

[swansont]

Not all of the light goes through the slit. But for all of the light that does, energy is conserved.

[Horza2002]

You don't get light and dark bands in a single slit experiment. You will only observe diffraction. To get the light and dark bands you need two slits so you can get interferance

[John Cuthber]

You don't get light and dark bands in a single slit experiment. You will only observe diffraction. To get the light and dark bands you need two slits so you can get interferance

 

 

What would your second guess be?

http://en.wikipedia.org/wiki/File:Diffraction1.png

[Horza2002]

How do you get an interferance pattern without interferance?

[swansont]

How do you get an interferance pattern without interferance?

 

The beam has a finite width. Any pair of rays within the beam have an opportunity to interfere, depending on the path length from their location in the slit to the screen.

[netrat]

You Do get the Light and Dark bands!

Im doing the experiment right now in my room and i clearly get the interference pattern on my wall.

 

Heres what I did:-

-Bought a Laser Pointer,

-bought two shaving razor blades.

-brought blades edges very close to each other.

-Fire lazer through small gap.

-WOW an interference Pattern!

 

 

Pattern is lot better than what it appears in the picture. I got a bad camera. LOL

Edited September 22, 2010 by zacinfinite

[Horza2002]

Arr yes, I was assuming only one photon was going through the slit at once...understand now!

 

Arr yes, I was assuming only one photon was going through the slit at once...understand now!

[netrat]

Arr yes, I was assuming only one photon was going through the slit at once...understand now!

 

Arr yes, I was assuming only one photon was going through the slit at once...understand now!

 

I believe, even if one photon passes through the slit, it will still show the interference pattern. because here wave nature of photon comes into picture and not the particle nature.

Edited September 22, 2010 by zacinfinite

[Horza2002]

Ok now im confused...if theres only one photon wave passing through the slit, how can it interfer with itself? I don't understand how a wave manages to interfer with itself...

[timo]

Pretty much the same way a water wave interferes with itself.

[netrat]

We are used to macroscopic world, seeing discrete particles. Particles behaving in Newtonian physics and Relativistic physics.

Think in terms of quantum mechanics.

Everything that exists, matter or energy has particle nature (as matter, and you can count them) and wave nature ( you cannot count wave)

 

When a single photon passes through a small gap [gap size should be near to wave length of particle], it acts as a wave of energy and not as a single countable particle.

Hence diffracting to different waves (of same wavelength) and thus interfering with each other.

 

A photon actually is a quanta (packet) of energy.

It could be Imagined as a ball containing energy in classical physics.

But here it is imagined as a stream of wave ( frequency representing energy of wave)

 

So my friend this is wonderful world of Chaos where matter has both particle and wave nature and energy also has matter and wave nature.

 

Another interesting fact:-

You can see interference in more massive particles.

Actually in everything you see.

 

Matter is just concentration of huge amount of energy. So matter has very high frequency.

Electron is a particle and shows interference. Even one electron shows interference. It has been done in laboratory.

 

So moral of the story is, if you throw a stone with very high speed through a narrow slit, it will show interference.

You May conclude that stone will appear beyond the slit as many stones of different masses, stone at the center being most massive and rest decreasing in mass as you move away from center.

 

!!!!!But that is not the case!!!!!!!!

 

Each time you throw the stone, The whole stone will appear beyond the slit in random places.

If each time you note the position of the stone, and after many such experiments you overlay the positions, you will see a clear interference pattern!

 

Conclusion:-

Bright spots are High probability areas [High probability of appearance of stone] and dark are lowest.

Edited September 23, 2010 by zacinfinite

[Horza2002]

I understand about interferance, diffraction and splitting in general (i.e. the double split experiment), I couldn't see how it managed to interfer with itself is all.

[IM Egdall]

Imagine a beam of light on the left going through a slit, then hitting a screen on the right. Say you make the slit narrower and narrower. Now the narrower the slit, the more accurately you know the location of the light at the slit. But as you narrow the slit, the diffraction pattern on the screen gets wider and wider. This means that where the light from the slit is going becomes less and less certain. In other words, the better we know the location of the light (at the slit), the less we know its direction. This is Heisenberg's Uncertainty Principle in action.

Edited September 23, 2010 by I ME

[Horza2002]

ARRRR thanks I ME that makes perfect sence to me now!