Double Slit Experiment

Isaac Newton (yes, that guy who discovered gravity through apples*) believed that light was a particle as it traveled in straight lines. Although many of Newton's contemporaries said light behaved as a wave. This is one of the experiments that shows the wave nature of light.

• Laser
• Old CD
• A thin wire, can be taken from an electrical wire
• Two small magnets
• Blades from two sharpeners
• Stand for the CD (I am using a book case, picture attached)
• Screen, white sheet of paper can also be used

On the CD, on one side attach the two magnets diametrically, on the either side of the hole in the center. On the reverse side, we can tape the thin wire. Now place the two sharpener blades such that the wire is in between and there is a very small gap between the wire and the blades. Viola! Slits made.

(The reason I am using a magnet to hold the blades, instead of tape or glue is that, the distance can be varied and changed conveniently)

You can refer to the video to understand this process better.

Now we take the contraption made in the previous step and hold it using the stand, which in my case is a book set. We level the laser at the same level as the slits. At a distance of about 2-3 metres, away from the slits, attach the screen, in our case a white sheet of paper to the wall.

You can refer to the video to check my set up

Fire the lasers!

This is going to get sciency.

There are two parts to this. First why is the projection, so wide instead of a single dot. The reason is the Uncertainty Principle due to which, when the light is just passing through the slit ie between the wire and blade, the uncertainty in the position of light is low, thus the uncertainty in the momentum of light increases and instead of the light landing on one defined spot, the room for error increases and the light can now land on a bigger area giving us the wide projection.

Second, why is the projection not smooth, but broken into these dots. This is because light is a wave! When light passes through both of those slits, two waves pass through those slits, thus wave interference is bound to take place. Wherever the light is bright, constructive wave interference take place and wherever it is dark destructive wave interference takes place. Refer to the attached animation, created by me, to better understand it.