Why does Diffraction work?

[Obnoxious]

Why is it that when you shine laser beam through the double slit, you get a whole bunch of dots?

[RedAlert]

I think he is referring to the double-slit experiment in quantum physics?

 

If so, we really don't know why light behaves like that when it goes through the slits. If we put a detecting device, it suddenly, magically, behaves once again like normal light. Once the detecting device is gone (or turned off), the light again behaves queerly.

 

However, that does not stop us from theorising. Some people say light can also travel in waves sometimes. This property of light is also known as the wave-particle duality. So in certain cases, like waves, light interferes with itself. That is why in the double slit experiment, lots of bars are formed.

 

I am not a great expert in quantum physics, but I am sure there are a lot of people here who can tell you other theories, or expand on the one I have briefly explained above.

[Asimov Pupil]

well the diffraction grating is so small that the wave of light hits the openning and is acts as another source except there are so many that it produces multiple dotswith destructive and constructive interference

[popjinx]

Light has been proven to act as a particle (http://www.britannica.com/nobel/micro/465_57.html) and as a wave, which was discoverd by Young through his famous double slit experiment. This experiment proved that light is infact a wave, an electromagnetic wave to be exact. Light waves have the same destructive and constructive properties as do sound waves. The reason you see a diffraction pattern is simply due to these properties. The light spots you see are due to constructive interference (light waves meet in phase) and the dark spots you see are due to destructive interference (light waves meet out of phase). The number of light and dark spots are created by a type of lense called diffraction grating (this how CD's work! http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio/95x6.htm .) Diffraction grating is a set of many parallel slits that disperse light according to the slit width-the smaller the slit width the more light that is dispersed and the farther apart the dark spots apear. So, by changing the slit widths, you can change the pattern of light and dark spots accordingly. I hope this helps!!

[5614]

Light waves have the same destructive and constructive properties as do sound waves.

Remember that light is a transverse wave carried by photons whereas a sound wave is longitudinal and carried by any medium... they are not quite the same thing.

[popjinx]

That is true, sound waves need a medium (air) to propigate through, where as light waves do not, they are propigated by their inherent electic and magnetic fields. I am sorry for any confusion.

[5614]

No confusion, I was just pointing something out. Air can travel through liquids or solids as well, in fact it travels worst through air out of nearly all other mediums!

 

Air can travel through any medium above a critical density... air having a low density is not amazing at 'conducting' sound but it is sufficient.

[popjinx]

Yes, I know...I was just citing air as an example of a medium. Thanks for keeping me on my toes!

[Primarygun]

Why is it that when you shine laser beam through the double slit, you get a whole bunch of dots?

The screen may burn if it is a thin paper, lol. Energy at the region with the colour of that laser are given more energy.

[swansont]

The screen may burn if it is a thin paper, lol. Energy at the region with the colour of that laser are given more energy.

 

The spot size depends on the slit size and distance to the screen, and much of the beam may be lost because it hits the solid part of the grating.