I'm Tech Adams. Welcome to my laboratories where we explore science
through technology and technology through science
today we're going to be looking at an at home experiment that you can do
that proves one of the fundamental properties of light that it behaves like
a wave
In the late 1700s one of the oldest
questions a science had yet to be proven experimentally
what exactly is light? Isaac Newton and others had proposed that light was a
particle
while Robert Hook and Christiaan Huygens held the belief that light was a wave
while the evidences seemed to point more towards the wave theory
the particle theory was more popular because Isaac Newton
was better known. In 1803 Thomas Young presented the results at his now famous
experiment to the Royal Society of London
in his experiment Young passed an control beam of sunlight through a card with two
slits and observed the light falling on the wall behind
Rather than seeing two pools of light which would've been consistent with a
particle theory
he observed wave interference bands, identical bans to what would have been
seen if waves of water had passed through a similar device
Young proved beyond any doubt that light behave like a wave. His theory would
remain widely unchallenged until the early 20th century when Albert Einstein
used the experimental data collected by Max Planck and Heinrich Hertz
to prove that sometimes light also behaves like a particle
Einstein's conclusion led us to the modern view of the nature
like called wave-particle duality which counter-intuitively
views it as both. The cool thing about any valid scientific experiment is that it's
reproducible -
others can follow the same procedure and get the same results. The cool thing
about the double slit experiment
is that it's reproducible at home. to do this experiment you'll need four things
scissors, electrical tape, a laser pointer and very thin wire -
32 gauge works well. Warning lasers are cool but can be dangerous
Class III lasers like the laser pointer that am using can cause damage to the eye or
to a camera under direct exposure
never look directly into a laser beam during operation
if you're using a laser with an output power greater than 5 milliwatts be sure
to be wearing appropriate eye protection in accordance with state
or national regulations. to build your own double slit apparatus
start by cutting two small strips of electrical tape and place them over the
lasers opening
leaving a relatively small gap. Shine the laser on a white surface
and notice with the spot looks like. Next carefully place a small strand of
wire across the opening
and hold it in place on each end with a piece of tape, keeping the wire straight as
possible
now carefully place two pieces of tape on either side the wire over the opening
getting the tape as close as you can to the wire without touching, it could take
a couple of tries to get this part right
And that's it
turn off all the lights and shine the laser on a white surface
notice how it used to be a single line is now dozens of vertical lines
diminishing in brightness the further away from the center as they go
unfortunately some lines that are actually visible
are not bright enough to appear on camera. Laser-light as a good substitute for sunlight.
Normal light sources radiate in concentric circles from the light source
making it a curve wave front that strikes a service nearby
but at a great distance like that between the Earth and the Sun the
curvature
the circle so small that it's like it's traveling as a group of parallel lines
Laser light also travels in a more parallel path which is what allows it to
travel much greater distance than the light from a flashlight
this straight wave front allows the double slit experiment to work. when the
straight wave front strikes double slit each
opening acts like its own light source and the radiation continues forward with
a more circular front
the two wave fronts interfere with each other creating the pattern of light and
dark spots on the far surface
using the same laser pointer method with a little bit of electrical tape, wire,
time, and patience you can also explore single slit diffraction
multi slit diffraction and component vector independence
in diffraction. This is what science is all about: repeatable experiments that
generate measurable results that lead to conclusions about the world around us
Is it possible to explain what's going on here if flight is only a particle
No! On the other hand their experiments they can only be explained if light is
behaving like a particle
which is why wave particle duality is the current theory about how light works
But in 1803 when this experiment was first conducted
all the data that they could generate pointed towards the wave-like properties
of light
and not its particle nature. It wouldn't be for another 100 years and the geniuses
of people like Planck
Einstein, and Heisnenberg that the theory would not be proven wrong
but proven incomplete. how many other modern theories will suffer the same
fate?
Who knows! But until we're able to collect more information by building
better and more accurate experiments based on what we already do know
will never find out. For Tech Laboratories, I'm Tech Adam, saying keep thinking
and thanks for watching. Have a question about today's episode? WAIT STOP
I forgot something cool!
see all these little dots around the main center beam in a laser pointer
Those are coming from interference generated by the particles actually generating the
photons
inside the laser diode. Pretty cool, right?
As I was saying before I interrupted myself, Have a question about today's
episode?
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