# Homework Help: Middle ear amplifies

1. Jun 22, 2012

### ilona

1. The problem statement, all variables and given/known data

Hei!
I have problem with this quest:
Middle ear amplifies the sound waves entering cochlea by 30dB. This means that in case of total dysfunction of ossicles the sound energy transferred into cochlea is reduced:
a)3 times b)30 times c)1000 times d)3000 times

2. Jun 23, 2012

### tiny-tim

welcome to pf!

hei ilona! welcome to pf!

total dysfunction means no amplification, so it's 30dB quieter

sooo … what is the definition of dB ?

3. Jun 23, 2012

### ilona

logarithmic unit of ratio of intensity to standard treshold of hearing(10^-12)
dB=log^10*I/Io

4. Jun 23, 2012

### ehild

That is almost the definition of loudness, but not quite.
Amplification is defined in terms of output intensity and input intensity. And you meant base 10, not log on the 10th power... and it is decibel, that "deci" means something...
See: http://en.wikipedia.org/wiki/Decibel#Definition

ehild

5. Jun 23, 2012

### tiny-tim

(try using the X2 and X2 buttons just above the Reply box )
isn't that B, not dB ?

6. Jun 23, 2012

### ehild

It is not anything. log without argument multiplied by I/Io...

7. Jun 23, 2012

### ilona

L(B)=log10*I/Io

but i wonder if there is no amplification we have 1 dB ,haven't we?
so why is not it just reduced by 30 times???

8. Jun 23, 2012

### ehild

9. Jun 23, 2012

### tiny-tim

yes, ilona, if I/Io = 1, then log I/Io = … ?

10. Jun 23, 2012

### ilona

log1= 0

11. Jun 23, 2012

### tiny-tim

right, if the amplification ratio is 1, then the dB difference is 0

and if the amplification ratio is 10, then the B difference is 1, and the dB difference (10 times as much) is 10

so if the amplification ratio is 100, then the B difference is … ?

12. Jun 23, 2012

### ilona

ok , i think answer will be 1000times

13. Jun 23, 2012

### ilona

but once again , cause I don't think I understand it..
I have this formula LB=log10p1/p0
so I have 30 dB so it is 3 B
and now why p1/po is 1?

14. Jun 23, 2012

### tiny-tim

yes
forget the formula

(you'll never remember it in the exam, anyway)

just remember ('cos it's easy) …

10 dB = 10 times louder

then you know that 1 B = 10 times louder, so 2 B = 100 times etc, and finally convert to dB by always multiplying by 10 (same as converting grams to decigrams, or metres to decimetres)

15. Jun 23, 2012

### ilona

ok, thank you very much =)