1)

Power ratio to dB = 10log 10 (P)

dB to power ratio = 10 ^ (dB /10) 

2)

dB means Decibel  which is 1/10th of Bel.

3)They allow simple numbers to express values that would normally require many more digits.

4) in signal communication, noise ratio level to find out value decibel system can be used.

5)dB calculation Represent Large Ratios With Simple Numbers.