is light particle or waves??!!

yess that's a big question.. long long time ago scientist confused whether light is a particle or a wave.. soo by the end of the 18th centuries Thomas Young set out an experiment to proof that light is a wave..

the experiment is using a light as the source, the double slit and the screen for observe the fringes.

the light is shield around. the double slit is placed at least one meter from the source and the screen place several meters from the slit. the experiment was taken in dark room. there are 3 important factors:

1. the slits are millimeter in width
2. the slits are about a millimeter apart
3. the slits and the screen is about several a meter

this experiment was for conclude that light has waves properties. to proof the fact that light showed interferences effects to conclude light traveled as a wave. this is achieved in the experiment by passing a single beam of laser light through the two slits. a the light passes trough, it is diffracted so it spread to the screen.

• determining λ

there are equation to determine wavelength, λ.

λ=ax/D

where:
λ:wavelength
a:slit separation
x:fringe separation
D:slit to screen distance

this equation derived from:

there are 2 ray made triangle (S1CX and S2CX). using phytagoras to write the expression:

S₁C² = S₁X² + CX² = D² + (x + a/2)²

S₂C² = S₂Y² + CY² = D² – (x – a/2)²

Subtracting it

S₁C² - S₂C² = (x + a/2)² - (x – a/2)²

We can write it like this:

(S₁C + S₂C)(S₁C – S₂C) = (x + a/2 + x – a/2)(x + a/2 – x + a/2) = 2ax

Now both equation very similar in length, so we can write like this:

S₁C + S₂C = 2D

This differences equal to one wavelength, λ:

S₁C - S₂C = λ

Substituting gives:

2D λ = 2ax

Then à λ = ax/D

this is the video about two slits experiment

http://www.youtube.com/watch?v=FeCV27-mk0I&feature=related

this is it about what is a light.. hope you understand it.

Thanks