Lecture20 - In the last couple of lectures we discussed...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: In the last couple of lectures we discussed waves on a string these are transverse waves, in which the molecules in the string oscillate up and down as the wave moves horizontally Sound is also a wave but its a longitudinal wave, in which molecules move back and forth along the direction of wave motion: Lecture 20: Sound Waves High pressure Small displacement Low pressure Large displacement High pressure Small displacement We can describe the sound wave either in terms of the pressure at a given point: or in terms of how much the air molecules have moved from their normal positions: The pressure and position amplitudes are related by p x , t ( 29 = + - ( 29 y x , t ( 29 = - + 2 = - ( 29 p max = BkA Note that here the displacement variable y is in the same direction as x Speed of Sound We found earlier that the speed of waves on a string is The velocity of any mechanical wave has a similar form What is the elastic property of a gas? Its the fractional change in volume for a given change in pressure v = Elastic property of string Inertial property of string B = - / Bulk modulus Now we need to find an inertial property for a gas This is the density So the speed of sound in a gas is: The same expression also works to find the speed of sound in a liquid The expression for a solid is similar: v = About 330m/s for air at 1atm and 20 o C v = / = Youngs modulus About 6000m/s for iron Intensity Weve already discussed the power transmitted by a wave now well see how much power is transmitted by a sound wave...
View Full Document

Page1 / 16

Lecture20 - In the last couple of lectures we discussed...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online