Question

The intensity level 1 m away from a source is 60 dB. Threshold intensity of hearing is ${10^{ - 12}}W{m^{ - 2}}$. If there is no loss of sound power in air then intensity level at 2000 cm from the source is:
(A) 45 dB
(B) 34 dB
(C) 35 dB
(D) 64 dB

Answer 1

Hint We should know that the intensity at which the stimulus, which can be heat or pressure begins to evoke the pain is known as the threshold intensity. We should know that the threshold of hearing is assigned a sound level of 0 decibels which can also be exclaimed to be as 0dB. Based on this concept it is required to solve this question.

Complete step by step answer:
We know that:
$I\alpha \dfrac{1}{{{r^2}}}$and $\Delta I = {I_1} - {I_2}$
So, we have to evaluate the above expression to get:
$10\log \dfrac{{{I_1}}}{{{I_2}}} = 10\log 400 = 26.02dB$
And we get that:
$10\log \dfrac{{{I_1}}}{{{I_2}}} = 10\log 400 = 26.02dB$
Hence the intensity level at 2000 cm away is 60 – 26 = 34 dB.

Hence the correct answer is option B.

Note We should know that for human beings the normal hearing is between -10dB and 15 dB, although in many cases 0dB from 259 Hz to 8 Hz is deemed to be known as the average normal hearing. The hearing thresholds of human beings and other mammals can be found with the behavioral hearing tests and the physiological tests which are used in audiometry.