Phys 101 Learning Object

1. Physics 101 Learning Object
Sound Intensity Multiple Choice Question
You are working for the Canadian Radio-television and Telecommunications Commission
(CRTC) and have received recent complaints from TV watchers that a recent ad played
on the air has been too loud. According to the CRTC guidelines, ads should not exceed
80.0 decibels. You decide to investigate this claim:
Q1. Upon investigating, you find that the sound intensity of the ad is 1.5*10-4
W/m2
.
What is the sound intensity of the ad in decibels?
A. 79.2 dB
B. 81.8 dB
C. 80.0 dB
D. 77.3 dB
E. 82.5 dB
Circle one: The ad violates/does not violate the CRTC guidelines.
Q2. In a seperate claim, an ad is measured to be 78.0 dB. What is the sound intensity
of this ad measured in W/m2
?
A. 6.9*10-4
W/m2
B. 3.6*10-5
W/m2
C. 6.3*10-5
W/m2
D. 7.1*10-4
W/m2
E. 5.8*10-5
W/m2
Circle one: The sound intensity of this ad is lower/higher/same compared to the first ad
Do the results make sense?

2. Solutions
Q1. Upon investigating, you find that the sound intensity of the ad is 1.5*10-4
W/m2
.
What is the sound intensity of the ad in decibels?
β = 0dB + 10log(I/I0)
= 0dB + 10log(1.5*10-4
Wm-2
/10-12
Wm-2
)
= 81.8 dB
A. 79.2 dB
B. 81.8 dB
C. 80.0 dB
D. 77.3 dB
E. 82.5 dB
As 81.8 dB exceeds 80.0 dB, the CRTC guideline is violated.
Circle one: The ad violates/does not violate the CRTC guidelines.
Q2. In a seperate claim, an ad is measured to be 78.0 dB. What is the sound intensity
of this ad measured in W/m2
?
β = 0dB + 10log(I/I0)
78.0 = 10log(I/10-12
Wm-2
)
log(I/10-12
Wm-2
) = 7.8
(I/10-12
Wm-2
) = 107.8
I = 6.3*10-5
W/m2
A. 6.9*10-4
W/m2
B. 3.6*10-5
W/m2
C. 6.3*10-5
W/m2
D. 7.1*10-4
W/m2

3. E. 5.8*10-5
W/m2
6.3*10-5
W/m2
< 1.5*10-4
W/m2
Circle one: The sound intensity of this ad is lower/higher/same compared to the first ad
Do the results make sense?
Yes, if the measured sound intensity in decibels is lower, then the sound intensity
measured in W/m2
should also be lower.