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Physics 1240
Homework 8 solutions
Brief solutions to homework set #8. Your numbers will be diﬀerent, but the idea is the same.
I’m just using sample numbers here.
1. 1. When I sing into a microphone, suppose I produce a sound intensity level (SIL) of 30 dB.
If you can sing at 50 dB, what is the ratio of our produced sound intensities (yours divided
by mine)?
For each (additive) increase of 10 dB, the intensity ratio increases (multiplies) by a factor of
10. Here there is an increase of 20 dB, so your sound intensity is 100 times larger than mine.
2. Let’s turn around the previous problem. Suppose that you and I are having a singing contest,
and you produce a sound intensity (measured in W/ m
2
) about 6.3 times greater than mine.
How many dB louder than me are you singing?
Check the table in the book to convert between sound intensity ratios and decibels for ratios
less than 10. Looking in the table, I see that an intensity ratio of 6.3 corresponds to an 8 dB
increase.
3. If the amplitude of a sound wave is quadrupled, by what factor will the intensity increase?
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This note was uploaded on 08/24/2010 for the course PHYS 1240 taught by Professor Holland,murray during the Spring '08 term at Colorado.
 Spring '08
 HOLLAND,MURRAY
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