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Confusion about decibel

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watertreader

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Hi,

Have a little confusion about decibel. I know that to obtain decibel of a power type of quantity you will use 10 log P. while for voltage you will use 20 log V.

However, if the physical quantity I am measuring is in power or intensity. But the output measurement I am taking is in voltage or current... which is the correct form which i should express decibel as?

THanks for your help!
 

Since you are measuring output power from output voltage the correct one is 20logV. You will recollect that power is related to V^2. So thats the extra factor that comes in as 20 instead of 10. Its that plain simple
 

The decibel is a kind of a relative measure of a quantity. Thus, the exact definition is given by 10 log (P2 / P1) or 20 log (V2 / V1), since power is proportional to square of voltage. Some special kind of decibels is dBm, where P2 = 1 mW. The decibel has been used since it represent the human perception well, especially the ears, etc.
 

well buddy visit this page and read it once..you thing will be clear
h**p://www.phys.unsw.edu.au/jw/dB.html
'njoi
 

P=V²/R=I²×R
Hence
10×log(P1/P2)=10×log(V1²/V2²)=10×log(V1/V2)²=10×2×log(V1/V2)=
20×log(V1/V2)=20×log(I1/I2)
 

There is no difference to use 10loP or 20 logV.
 

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