Decibel is the unit of

Learned Indian classical vocalists do not like the accompaniment of a harmonium because

$A$ hearing test is conducted on an aged person. It is found that her threshold of hearing is $20 \, dB$ at $1 \, kHz$ and it rises linearly with frequency to $60 \, dB$ at $9 \, kHz$. The minimum intensity of sound that the person can hear at $5 \, kHz$ is

Quality (or timbre) of a sound depends on:

How many times more intense is a $60 \ dB$ sound than a $30 \ dB$ sound?

The power of sound from the speaker of a radio is $20 \text{ mW}$. By turning the knob of the volume control,the power of the sound is increased to $200 \text{ mW}$. The power increase in decibels as compared to the original power is $.... \text{ dB}$.