There are two interesting cases to talk about. Many waves are even simpler than that - the magnitude of the combined oscillation is simply the sum of both waves. When these two wave collide with, they add up to form a single disturbance. Now, imagine two identical waves travelling through space. It's a nice video that should teach you the basics of waves. I added a video from Veritasium's channel that talks about waves. For our purposes, we should consider a simple case where these waves are periodic in time. In the case of sound waves, for example, this "field" is the air-pressure around us - sound waves are simply disturbances to the air pressure that travel through space. We all know what waves are from our everyday lives, but what are they, really? and it's beautiful! One of my favorite wave phenomena are related to wave interference, which lead to interference patterns. Once you study what waves are, you begin to see them everywhere. In my opinion, it helps you develop intuition and see the world differently. This makes the study of waves an extremely important part of the education of physicists. Whether it's the waves on the surface of a pond or a vibrating string which are usually described by Newtons laws, light, which is an electromagnetic wave, gravity waves described by Einsteins theory, or miniature particles described by wave mechanics (aka Quantum Mechanics) - they all share many similar properties. There are many universalities to these theories, but my favorite is that they can all describe waves. You start with the basics - mechanics (Newton and his buddies from the 18th century), and gradually move towards the 19th century where you learn about electro-magnetism (Maxwell and such) and eventually you get to Quantum Mechanics and Einsteins relativity. So interference patterns look cool, but so are many other things!! why should we study them?Īs a physicist you get to study how things work. If you find physics interesting I suggest you read through (at least the introduction part!) before you skip to the pictures and videos and how-to's! * This instructable can seem a bit technical, so feel free to ask me stuff! I will also teach you how to use your laser to measure tiny objects, like the width of your hair!! It's super easy! I determine the wire to be 0.47 mm diameter from this measurement - right where the calipers put it.Long story short: You will learn how to observe interference patterns at home (using the cheapest laser point you got). I set the pointer and wire up much further from the wall (28.5 1 foot tiles - right across the big room) and could see 26 fringes (you lose count near the middle but can extrapolate by counting what you can: I see 9 peaks on 14 squares, and N peaks on just over 40. Measured diameter was 0.46 - 0.49 mm (often wire is not perfectly circular. I just repeated this slightly more carefully with a wire I had at home. With stuff you have lying around your office. With a bit of care you can do even better. And you can see quite easily see all the way out to the 20th peak if we assume you can center these peaks better than 1/4 of their spacing (really that is not hard) your accuracy will be better than 2% ($\frac$). For greater control over the measurement, you could rotate the graph paper until you exactly found an integer number of blobs between your lines the angle would give you some "fine tuning" of the measurement. You can get quite good accuracy with this method, assuming that you have a known wavelength for your laser pointer. In the above case, I calculate that $d = 0.69 mm$ diameter - indeed, it was a pretty thin wire I had lying around (somewhat smaller than 1 mm). The equation for the peak spacing is given from basic straight slit diffraction: for wire thickness $d$, distance to the screen $D$, wavelength $\lambda$, the spacing $w$ between peaks is given byĪnd so the thickness of the wire can be deduced from And if you can't bend your wire, or you don't have enough to stack it up, that doesn't matter either. By increasing the distance, and in particular by increasing the distance until you get an integer number of peaks falling on an integer number of squares on your grid, you can get almost any accuracy you want with things you already have lying around. I count slightly less than 10 peaks for 3 squares on my paper (1/4" squares), with a green laser pointer (wavelength 532 nm) at a distance of about 2.5 m from the screen.įrom this you can calculate the thickness of the wire. The point is that I can see a series of "blobs" that correspond to diffraction peaks from light that goes around my wire. exposure could have been better, and I could have put a beam stop in in order to avoid the overexposure of the central beam.) You will see the following diffraction pattern: Laser pointer, wire, screen at known distance.
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