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$\bullet$ (a) If the amplitude in a sound wave is doubled, by whatfactor does the intensity of the wave increase? (b) By what fac-tor must the amplitude of a sound wave be increased in orderto increase the intensity by a factor of 9$?$

a) the intensity is increased by a factor four.b) the amplitude must be increased by a factor three.

Physics 101 Mechanics

Chapter 12

Mechanical Waves and Sound

Periodic Motion

Mechanical Waves

Sound and Hearing

Rutgers, The State University of New Jersey

Simon Fraser University

University of Sheffield

University of Winnipeg

Lectures

08:15

In physics, sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound above 20 kHz is known as ultrasound and has different physical properties from sound below 20 kHz. Sound waves below 20 Hz are called infrasound. Different species have different hearing ranges. In terms of frequency, the range of ultrasound, infrasound and other upper limits is called the ultrasound.

04:49

In physics, a traveling wave is a wave that propogates without a constant shape, but rather one that changes shape as it moves. In other words, its shape changes as a function of time.

01:55

(a) If the amplitude in a …

01:01

If the amplitude of a soun…

01:43

(II) If the amplitude of a…

01:03

If the pressure amplitude …

02:28

If the intensity of a soun…

When two light waves, both…

03:01

A certain sound source is …

02:00

02:13

03:45

The intensity of a sound w…

04:28

A certain sound level is i…

01:35

Two waves having the inten…

So for part, we know that the intensity equals a power divided by an area. So it's similar to, I would say, um I guess an energy flux per second. Um, but based on this, we know that the intensity is going to be directly proportional to the amplitude squared. So we can say that and the intensity sub one divided by the intensity sub two is going to be equal to a sub one squared, divided by a sub two squared. Now we know that Ace of two equals twice that of a CE of one. And so we can say that ice of one divided by ice up to will simply be equal to a sub one divided by two times a ce of one squared. And so we know that ice up to is going to be equal to four times I sub one. So if the amplitude is doubled, the intensity is quadrupled and this will be your answer for party for part B. They want the intensity to be increased by a factor of nine. So for part B ah, I sub one divided by ice up to rather sorry, this would be your answer for party and then for part B. I suborned by bicep to this would equal a sub one squared, divided by a sub two squared. And we know that I said to needs to equal nine times ice of one. So essentially a sub one divided by a sub too squared will equal nine rather one over nine, because again it ice up to is 99 times greater, and I support it. And so we find that Ace up two squared will equal nine times a sub one squared, which means that a sub two equals three times a so won. This will be your answer for a part B. So if you want to increase the intensity by a factor of nine, you're going tohave to triple triple the amplitude. That is the end of the solution. Thank you for watching

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