Which decibel value most closely represents a power increase from 5 watts to 10 watts?
Why Decibels compare powers on a logarithmic scale: dB = 10 x log(P2/P1). Going from 5 W to 10 W is a ratio of 2, and 10 x log(2) = 3.01, so about 3 dB. Doubling power is always close to 3 dB no matter what the starting wattage is.
Watch out The choice of 2 dB comes from mistaking the power ratio of 2 for the decibel number, and 5 dB looks like the 10 minus 5 difference in watts, but decibels come from the ratio put through a logarithm, not from subtraction.
Double the power = +3 dB, half the power = -3 dB. Ten times = 10 dB.