physics 101

1. Wave and Oscillations
Sound Waves
Physics 101
LO4

2.  You are standing 10 meters away from a House that is
under construction the sound intensity level from
where you are is 70dB.
Intensity
10 meters
1

3.  What is the sound intensity of the construction?
 Hint: I (dB)b=10log10[I/I0]
b(dB)=intensity level
I0=1x10-12 W/m2 (is a constant)
I=?
 Answer: version a)I/I0=10-12(1070/10)
I=10-4 W/m2
version b) 70=10log10[10-4/10-12]
I=10-4 W/m2
Question 1a)

4.  How much power is the construction radiating?
 Hint: use the formula P=I4(pi)r2
 Answer:
P=10-44(pi)102
P=0.126W
Question 1b)

5.  What would the sound intensity and sound intensity
level(dB) be if you doubled the distance?
 Hint:
 Answer: I=P/(4(pi)r2)
I=0.126/(4(pi)202)
Sound intensity I=2.51x10-5
b = 0dB+ 10log((2.51x10-5)/(10-12))=55.29
Sound intensity leveldB=55.3
Question 1c)

6.  How many houses under construction can you add to
equal 90dB?
 Answer: b(90)-b(70)=20dB
I/I0=107
I’/Io=109
log10(I’/I)=2
I’/I=102
I’=10^2I
100 times more construction to meet the 90dB of sound
intensity.
Question 1d)