#### Answer

10 times.
1,000 times.
1,000,000 times.

#### Work Step by Step

The decibel scale is logarithmic, based upon powers of 10. Whenever the intensity of sound is increased by a factor of 10, the intensity level increases by 10 dB.
a. A sound of 10 dB has an intensity 10 times greater than 0 dB, the threshold of hearing.
A sound of 10 dB corresponds to an intensity of $10^{-11} \frac{W}{m^{2}}$, which is $10^{1} = 10$ times greater than the intensity of a 0 dB sound, $10^{-12} \frac{W}{m^{2}}$.
b. A sound of 30 dB has an intensity 1000 times greater than 0 dB, the threshold of hearing.
A sound of 30 dB corresponds to an intensity of $10^{-9} \frac{W}{m^{2}}$, which is $10^{3} = 1000$ times greater than the intensity of a 0 dB sound, $10^{-12} \frac{W}{m^{2}}$.
c. A sound of 60 dB has an intensity 1,000,000 times greater than 0 dB, the threshold of hearing.
A sound of 60 dB corresponds to an intensity of $10^{-6} \frac{W}{m^{2}}$, which is $10^{6} = 1,000,000$ times greater than the intensity of a 0 dB sound, $10^{-12} \frac{W}{m^{2}}$.
This is discussed on page 394, and shown in Table 21.1.