Have a look at what is happening to the right of the slits. The experiment is named after the guy who first carried it out – Young’s double slit experiment. What happens if there are two or more slits? We’ll end up with two or more diffracting waves, which we might expect to interfere with one another.īelow is a simulation of diffraction through two slits. So far we’ve only considered the case of a single slit or gap for the wave to pass through. The video below shows how you can use this method to work out how wavefronts are altered by a slit.ĭiffraction Through Two Slits Young’s Experiment For example – if you dropped a number of pebbles in a straight line, all in one go at exactly the same time, a straight (in science-speak plane) wavefront would be created. These wavelets superimpose and interfere to form more complicated wavefronts. A wavelet can be described as a circular wave much like the ripple you would get from dropping a small pebble into a pond. Huygens argued that a wavefront could be modelled as a series of wavelets. One way to explain diffraction is to use a mathematical method invented by 17th century physicist Christiaan Huygens. When the gap size is smaller than the wavelength (top movie), more diffraction occurs and the waves spread out greatly – the wavefronts are almost semicircular. When the gap width is larger than the wavelength (bottom movie), the wave passes through the gap and does not spread out much on the other side. slit is narrower than the wavelength Gap width = two wavelengths i.e. When the size of the gap changes, how does this change the diffraction of the wave? When does maximum diffraction occur? (Think about your previous findings on the diffraction of sound around an obstacle). The difference between the movies is the size of the gap. This is shown in the two animations below. Since different colors diffract by different amounts, white light seen through a diffraction grating will spread out into its component colors as shown in this YouTube of incandescent and florescent diffraction.Diffraction also occurs when a wave passes through a gap (or slit) in a barrier. A diffraction grating is a piece of glass or plastic with a series of very small grooves, each of which acts like a slit.Why is the light pattern complicated instead of a simple spot? What is the difference in the light pattern between the single slits and the double slits? Finally the laser is shone through a series of double slits. Then the laser is shone through single openings of different sizes. The first is a square opening, the second a hexagonal opening. A red laser beam is shone through several different small openings. Notice that the plane waves on the right spread out into a circle on the left after passing through the small opening. You are looking down onto the surface of a tray of water. Here water waves travel through an opening about the same size as the wavelength and change their direction. Likewise sunsets are orange because when the sun is on the horizon the path the light travels to reach us passes through more atmosphere and even more violet/blue is removed. The sun looks a little more yellow than it really is because the violet/blue part of the spectrum has been removed (scattered out in other directions). Violet and a little blue light is scattered but since our eyes are not as sensitive to violet we see the blue. The sky is blue because clusters of nitrogen and oxygen molecules (which make up most of the atmosphere) have resonances at the same frequency of violet light. The wave is first absorbed and then re-emitted in all directions (or sometimes perpendicular to the incident direction). Scatteringis a similar phenomenon that occurs when a wave interacts with an object that has a resonance frequency the same as the wave frequency. We only notice diffraction when the opening or object is close to the size of the wavelength, so to see diffraction of light it needs to pass through a much smaller opening than a doorway.
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