The document discusses the perception of sound intensity, using a scenario of a crying baby on an airplane at 95 dB. It includes calculations on how distance affects perceived loudness and questions about sound reduction using noise-canceling headphones. It provides clicker questions with multiple-choice answers related to the impact of distance and noise cancellation on sound perception.

1. Sound: Power and Intensity
Real World Applications
PHYS 101 LO4
Timothy Cheng

2. Context
• You are flying home for the summer. As you
board the airplane, you discover there is a
crying baby onboard. The crying baby
averages 95 dB 10 cm away. Assume the noise
is radiated isotropically within the plane.
• Note: The human ear perceives 10 dB increase
as 2 times as loud and 10 dB decrease as half
as loud.

3. Part A
• How far do you need to sit away from the
crying baby to make the noise seem to be
as loud as sitting 0.1 meter away?
Given:

4. Clicker Question
• Choose the closest answer:
a) 10 m
b) 20 m
c) 30 m
d) 40 m
e) 50 m

5. Clicker Question
• Choose the closest answer:
a) 10 m
b) 20 m
c) 30 m
d) 40 m
e) 50 m

6. Solution A: Explanation Part 1
• First solve for total Power radiated by baby:

7. Solution A: Explanation Part 2
• Understand the relationship between change
in dB and perceived change in loudness.

8. Part B
• You happen to have a pair of Bose QC25
reduces noise by 15 dB via its latest noise
cancellation technology. Wearing this pair of
headphone, how far can you sit while the
sound is ¼ as loud as sitting 0.1 meter away?

9. Clicker Question
a) 17.8 cm
b) 17.9 cm
c) 22.8 cm
d) 27.8 cm
e) 27.9 cm

10. Clicker Question
a) 17.8 cm
b) 17.9 cm
c) 22.8 cm
d) 27.8 cm
e) 27.9 cm

11. Solution B: Explanation