Thomas Youngs House

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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? Ask it in the comments or on Facebook and Twitter, and subscribe for more weekly science and technology videos.