00:01
Okay, so we know that for a point a, three meters away from a source of sound, okay, the intensity, sound intensity level, okay, it's 53 decibels.
00:22
So we want to know what is the intensity at this point a.
00:26
So we know that intensity and sound intensity are related by this relationship, okay, and thence the algorithm of e times e zero.
00:45
Remember this is a number, a fixed number.
00:51
Okay, so if we rearrange for this, for this intensity, that is actually the value we want to find, we know.
00:59
That is going to be 10 times beta divided by 10 times the intensity 0, which is 10 to the minus 12 watts per square meter.
01:19
Okay, so we just use this data to find that the intensity is 10 times beta, that has 53.
01:30
Divided by 10 and multiplied by 10 to the minus 12 watts per meter square.
01:39
And if you do these calculations, you are going to find that this is 1 .99 times 10 to the minus 7.
01:49
Okay, watts per square meter.
01:53
And you can just approximate this to 2.
01:57
And this is the result for the a part.
02:05
Okay, so for the b part, we want to know what is the distance for the intensity to be one -fourth of the intensity at the point a.
02:20
So we know that the relationship between distance and intensity is given by this equation that the radio of intensities is the radio the square radio of distances okay so we rearrange we know that this is going to be true and that the first distance or distance say is going to be three meters and we want to know which which one is the second distance for which this is true.
03:00
Okay, so we can just rearrange for r2, so we find that r2 is going to be r1 times the radio, the square root of the radio of the intensities.
03:18
Okay, so we just use the data we know here...