University:
Boston University
Course:
CAS PY 105 | Physics 1
Academic year:

2024
Views:

119

Pages:

3
Author:

rias1s1zo5uq9

Superposition of Sound waves First show them the demo: Demo consists of two speakers hooked up to signal generator and amplifier. Set speakers several meters apart, and play a signal through them of a sine wave at a single frequency. Then tell students to walk the distance between the speakers. Ask them what they hear, if they hear anything funny. What’s going on? See if they can tell you. How much they can tell you depends on how much they already know about sounds and waves. - How does sound travel through the air? o By waves, sounds waves - How do the waves move through the air, I mean, air is pretty empty, it’s not like the string used to make the telephones you made, or the slinky itself? o Hopefully they’ll get that the particles in the air move it. - What does a sound wave look like, transverse or longitudinal? (show examples with slinky) o Longitudinal, or maybe they don’t know. - Longitudinal waves are also sometimes called pressure waves, why do you think that is? o They propagate by differences in pressure along a distance (again show the slinky and which areas represent high pressure and which represent low pressure) - What causes high and low pressure regions in the air? o The position of the particles in the air, moving back and forth - What does this have to do with what we heard from the demo, you’re probably asking? o Let’s find out. First let’s follow one particle within the applet and see its motion. o It looks like a wave, doesn’t it? Someone come draw what it’s doing on the board Kinda looks like this: Wow, so that actually kind of looks like a transverse wave, cool. - So if that’s going on due to the sound that’s coming out of both speakers, that are facing one another, what happens when the sound meets? o The waves run into each other. o This is called superposition of waves - And what have you already learned about what happened when two wave pulses traveling the opposite directions run into each other? o When the hit each other they add – wave gets bigger - What effect does that have on the sound if those are two sound waves? o Sound gets louder – this is called constructive interference - So what do you think would happen if a peak from this wave traveling to the right hits a trough of this wave traveling to the left? o If they still add the same way, you’re adding –1 to 1, get 0 - What does that mean for the sound? o There is no sound!! – this is called destructive interference - View superposition applet: o just instead of the waves passing through you, you’re passing through the waves as you walk