00:01
As we know, sound waves are divided into three categories that cover different frequency ranges.
00:08
Audible wave lie within the range of sensitivity of human ear that can generate it in a variety of ways, such as by musical instruments, human voices, or loudspeakers.
00:21
Second is, infrasonic waves have frequencies below the audible range.
00:27
Elephants can use infrasonic waves to communicate with one another even when separated by many kilometers third is ultrasonic waves have frequencies above the audible range you may have used a silent whistle to retrieve your dog dogs easily have the ultrasonic sound this whistle amids although human can't detect it at all.
00:57
Ultrasonic wave are also used in medical imaging.
01:02
As we know, the harmonic position function is given by s of x of t is equal to s max times cost kx minus omega where s max is equal to a is the amplitude of the maximum position of the element relative to equilibrium, k is equal to 2 pi by lambda is the wave number and omega is 2 pi by t is equal to 2 pi new is the angular frequency.
01:47
Now as we know the variation in the gas pressure delta p measured from the equilibrium value is also periodic with the same wave number and angular frequency as for the displacement which is given by delta p is equal to delta p max sign k x minus omega t where delta p max is equal to b s max k is equal to ro v omega s max is the pressure amplitude or the maximum change in pressure from the equilibrium value as we know that the power is the rate at which the piston is doing work on the element at any instant of time is given by power is equal to f times b of x vector also we can express the power as delta pi times b s over b t i is equal to ro v omega square a s square max sine square k x minus omega t as we know the intensity of wave i is defined as the power per unit area which is the energy transported by the wave transfer through a unit area perpendicular to the direction of the travel of the wave, where i0 is equal to 1 into 10 to 10 to power minus 12, what per meter square is the reference intensity.
04:22
Now, the intensity i is average power divided by a.
04:32
Let's put the equations over here.
04:34
So we can write 1 half ro omega square s square max times v.
04:45
That will be equivalent to delta p max square upon 2 row v.
04:58
That is my intensity i.
05:05
Also we know that for the spherical wave, the intensity is given by i is equal to average.
05:20
Power divided by 4 pi r squared because the waves are spherical over here at no we should define the sound level concept the sound level beta is convenient to use a logarithmic scale so beta is equal to 10 log i over i 0 as we know the sound of a vehicle's horn changing as the vehicle moves past you.
06:01
The frequency of the sound you hear as the vehicle approaches you is higher than the frequency you hear as it moves away from it...