![]() ![]() The second member of Team Light is next to press the buzzer. “That is one point each!” Round 2: Wave or Particle? Diffraction also makes sure that you hear your parent’s voice calling you for dinner even when playing behind a corner ( Figure 1D) and that ticket holders at a concert can hear the music quite well, even if they are sitting behind a pillar. A person speaking really quietly at one spot under the huge domed roof can be heard on the other side of the dome because sounds of higher frequency (like the ones produced while whispering) cling to the surface of the dome and travel longer distances than those produced while talking normally. Paul’s Cathedral, London, and New York City’s Grand Central Station work the same way. For example, traffic noise can reach houses even if they are behind a barrier ( Figure 1C). Interference is what makes noise-canceling headphones work.” Team Sound goes on to explain that sound diffraction can enable sounds to travel in unexpected directions. “When sound waves experience interference, the same thing happens. “But sound is a wave, too!” shouts their captain. Just then, Team Sound presses their buzzer! This can happen on the surface of a CD: white light hits the thin lines on the CD’s surface and they act like a prism, splitting light in multiple colors as it bounces off” ( Figure 1B). Diffraction can also be observed if waves are forced to pass through, or bounce against, very small openings. Diffraction allows us to see sun rays even when the sun is hidden by a cloud. “ Diffraction is observed when a wave encounters an obstacle and bends around it. Team Light’s second member sits up proudly. “Can you tell us more about diffraction?” “That is so interesting!” says the referee. This happens because diffraction transforms the doorway into a source of sound itself (photograph credits: A, B ). (D) Sound can also “go around a corner,” even when line of sight is blocked. This “leakage” of sound is a common problem when designing barriers for motorways, which is solved by adding hat-shaped elements on top of the barrier: these trap the long wavelengths and therefore make the barrier more effective. (C) Sound diffraction can cause traffic noise to make it past a barrier, because the wavelength of the low-frequency noise is bigger than the barrier. (B) Diffraction on the surface of a CD.Figure 1 - (A) Interference pattern over the thin film of a soap bubble.In bubbles, constructive interference happens between the waves reflected from the outside surface and those reflected from the inner surface, so that each color (i.e., each wavelength) appears very strong in some places and very dim close by ( Figure 1A).” Interference is what makes soap bubbles and peacock feathers look so colorful. When peaks meet up with troughs, the peaks and troughs cancel out, creating a smaller wave and dimmer light. He showed that when the peaks of two waves line up, they add together, creating a bigger wave and brighter light. A scientist named Thomas Young demonstrated this really well in a famous experiment called the “ two slit experiment”. Interference happens when two waves meet in the same space and affect each other. Wavelength is the distance between one peak in the wave and the next. ![]() Team Light replies, “Light travels as a wave, with high peaks and low troughs just like waves on the ocean. She then asks, “Could you please explain what those words mean?” “Correct!” says the referee, giving Team Light a point. Looking around proudly, the captain adds, “This means we can experience interference or diffraction.” Team Light is the first to hit the buzzer. The referee introduces the rules: teams score points by telling the audience about things that make their topic special. On the right is “Team Sound,” wearing DJ hats and t-shirts with musical notes. On the left side is “Team Light,” wearing t-shirts with an image of a lightbulb. There are two teams of three people each, sitting at desks facing each other, with a referee in between them. Imagine being in the audience at a TV studio, waiting for a quiz show to start. The future of shaping and designing sound is in the making! Maybe someday, sound experts will even teach something to light experts! We will tell you about acoustic metamaterials, an emerging technology that is quickly becoming part of our loudspeakers, our shows, our cars, our public spaces, and our hospitals-all the places where we want control over sound and noise. So, why do we not have lenses or displays for sound? Or do we? This article will tell the story of how sound technology is catching up with light technology. Light and sound are very similar: they are both waves, and they both have particles associated with them. Lenses and holograms are part of our everyday lives. The science of light manipulation started with the ancient Greeks, so we have had many years to develop it. ![]()
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