Two strings, one thick and the other thin, areconnected to form one long string. A wavetravels along the string and passes the pointwhere the two strings are connected. Whichof the following changes at that point:A. FrequencyB. PeriodC. Wavelength

Sound waves

Longitudinal Speed of sound

Sound waves Velocity of sound in

air at 20o is 343 m/s

Helium is lighter than air

Velocity of sound in

helium at 20o is 972 m/s

Hzmsmvf 343

1/343

Hzmsmvf 972

1/972

Sound tend to travel faster in liquids and solids (the molecules are closer together).

The velocity of sound in airvin air = 343 m/s

The velocity of sound in liquidvin water = 1490 m/s

The velocity of sound in a solidvin Aluminum = 5100m/s

Cool experiment – make a milkshake!

Why do we not hear collisions and explosions from outer space?

In a vacuum there are not any molecules –Without molecules we cannot have a pressure wave

–Sound cannot travel through a vacuum.

Sound in a vacuum Demo

JOHN 14:27Peace I leave with you, my peace I give to you: not as the world gives, give I to you. Let not your heart be troubled, neither let it be afraid.

Intensity of soundIntensity depends on __________

and the _____________ from the source.

24 rPower

AreaPowerI

PowerDistance

Spherical Waves / Plane Waves

Decibel Scale

Zero decibels refers to the threshold of hearing

 

 

log (10x) = x log 10 = x

10logx=x

log(ab)=log a + log b

log(a/b)=log a - log b

Decibel Scale

Zero decibels refers to the threshold of hearing

 

 

At a rock concert a meter placed at 2 m in front of a loudspeaker measures 130 dB. What is the power output of

the speaker?

At a rock concert a meter placed at 2 m in front of a loudspeaker measures 130 dB. How far away do I need to stand to be at a safer level of 90 dB?

If you increase the intensity by a factor of 1000, add ____ to the

decibel level.a) 3 dBb) 10 dBc) 20 dBd) 30 dBe) 60 dB

If you increase the intensity by a factor of 2, add ____ to the

decibel level.a) 3 dBb) 10 dBc) 20 dBd) 30 dBe) 60 dB

Can you detect a 3dB difference (50% loss)

http://www.phys.unsw.edu.au/jw/hearing.html

Other Decibel Scales

Weighting dBm dBV dB SPL dBFV

Q15-2

Consider music from a radio. If I turn up the volumeso that the sound level is 20 dB louder, by what factorhas the intensity increased?

(a) 10(b) 20(c) 100

Q15-3

When I sit one meter from a radio, the sound level is80 dB. How far from the radio should I sit to reducethe sound level to 60 dB?

(a) 3 m(b) 10 m(c) 30 m(d) 100 m(e) 300 m