Video · + 3 min read
Introduction
Alright so today we will discuss an experiment that initiated a movement that leads up to the crazy, yet awesome, idea of light having a dual-nature: The Double-Slit Experiment.
Ready to begin?
Who?
Can you guess who conducted this astounding experiment?
The Purpose?
Thomas Young, a brilliant lad like yourself, conducted this experiment in the year of 1801. Through this, he wanted to demonstrate that light can have the properties of a wave (which was radical, as Issac Newton already convinced most of the world that light has the properties of a particle).
Ready to move on?
How?
The experiment itself has a simple construction. All you need is:
1.) A source of light (sunlight works too!)
2.) Two flat surfaces/screens. One should have two small vertical slits while the other has nothing done to it. (while same size is nice, it is not 100% necessary)
3.) (preferable for visibility/not completely necessary) A container to place the surfaces/screens.
Note: A cardboard box (or any opaque container with a dark open space/black body inside when closed) can suffice for both 2 and 3!
To perform this experiment, you need to place the surface/screen with the two vertical slits parallel to the other screen with some distance (12 inches should be ok at the very least). Make sure that they stay parallel and that the surface/screen with slits is above/on top of the other screen. Then, shine your light source through the two slits and look inside!
If you have a cardboard box (or any opaque container with a dark open space/black body inside when closed) you can make a two vertical slits on just one side of the box, close the box, shine the light source, and look through, since the opposite side can work as the other screen.
Ready to move on?
What is Happening?
Through this experiment, as you may notice, you will see something that looks like waves on the spot at which the light is being shone on the second (no-slit) surface/screen. What is this? Well this is a three step process that is occuring.
First is that the light is shining towards the first surface/screen (with slits) and its light waves have no interference. It just travels to the screen untouched.
Second is the moment that the light waves pass through the two slits, they are "divided" into two separate waves.
Third is that while the two waves are traveling to the second surface/screen they interfere with each other and what you can see on the second surface/screen is the interference pattern (which looks like a wave!)
Think of it like this, imagine that you are sitting next to (or in front of) a pond and you decided to make waves by tapping the water with a paddle with one hand. Now you only see one set of waves traveling with no interference. However, now you decide to simultaneously make waves by tapping the water with another paddle in your other hand. Now you have two sets of waves traveling at the same time and they collide, making an intereference pattern (and a bunch of new sets of waves)!
Here's a nice diagram with a visual explanation (for all you visual learners!)
Ready to move on?
Why is this Only True if Light had Wave-Like Properties?
If light had properties of only particles, instead of seeing a wave-like interference pattern, we would see two solid spots that are approximately the same size as our slits.
Here's a nice visual explanation (for all you visual learners!)
Ready to move on?
Concluding Remarks
Eventually, by the work that followed Young's by August Fresnel, James Clark, James Maxwell, and Heinrich Hertz, the idea of light having wave-like properties was accepted. Thus light has a property called "wave-particle duality" (also called the dual nature of light).
Alright, so this lesson didn't really get into the hard quantum-mechanical applications and implications, however that is for you to dive into if you really are ambitious (it is difficult stuff to cover in one lesson so I skipped it). OR if you want, you can look at my lesson on photons which does have the quantum-mechanical fun! I hope you understood the basics and I hope this was enjoyable!