# Three Physics Problems

Three homework questions. I didn't post them in the homework section because I can't even attempt them because my professor didn't even explain them well enough for me to be able to do that. I'm not looking for specific answers, but more just a simple explanation of how to do the type of problem in general. Here goes:

A clarinet plays a soft note with a SIL of 40 dB. By what factor must the intensity be increased in order to play the same note at a SIL of 70 dB.

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If the whirring of a single fan produces a SIL of 50 dB, how many identical fans would need to be operated simultaneously to make a SIL of 63 dB?

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A 100-Hz sawtooth wave and a 202-Hz sine wave are sounded simultaneously. What is the frequency of the resulting beats?

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I just need formulas, really.

## Answers and Replies

vanesch
Staff Emeritus
Gold Member
Three homework questions. I didn't post them in the homework section because I can't even attempt them because my professor didn't even explain them well enough for me to be able to do that. I'm not looking for specific answers, but more just a simple explanation of how to do the type of problem in general. Here goes:

A clarinet plays a soft note with a SIL of 40 dB. By what factor must the intensity be increased in order to play the same note at a SIL of 70 dB.

What's the relationship between a sound intensity level in dB and the intensity of the wave ?

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If the whirring of a single fan produces a SIL of 50 dB, how many identical fans would need to be operated simultaneously to make a SIL of 63 dB?

Same as previous, plus: how does the intensity increase when two incoherent sources are put together ?

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A 100-Hz sawtooth wave and a 202-Hz sine wave are sounded simultaneously. What is the frequency of the resulting beats?

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What's the relationship between the frequency of the beats and the frequencies of the composing fundamentals ?

I just need formulas, really.

I think the point of the homework was to make you recall the right formula. Everyone can put in the numbers when he/she has the formulas, that's really really not difficult. The homework wanted to see if you understood the course material well enough in order for you to pick the right formula. So giving you the formula would be doing the essence of your homework for you.

I move this to HW...