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Waves, Light and Sound
Quick questions on Sound waves: N(A)-Level Physics waves
3short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is sound as a longitudinal wave?Show answer
Sound is made when something vibrates, such as a speaker cone or a guitar string. The vibration pushes the nearby particles back and forth, and they pass the disturbance on. This makes sound a longitudinal wave: the particles vibrate along the same direction the wave travels, creating regions where particles are squashed together and regions where they are spread out.
What is sound needs a medium?Show answer
Because sound travels by making particles vibrate, it needs a material (a solid, liquid or gas) to travel through. It cannot travel through a vacuum, because there are no particles to vibrate. This is why there is no sound in space, and why a ringing bell in a jar goes silent as the air is pumped out.
What are echoes?Show answer
An echo is sound that has reflected off a hard surface and come back to the listener. Because the sound travels to the surface and back, the total distance is twice the distance to the surface. Using speed distance time, you can find a distance from the echo time, remembering to halve the total for a round trip.
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