Acoustics and Sound Waves

For every 10dB, intensity rises by 10 times, so for 50 dB intensity will rise by $10^5$

The threshold rises from 20 dB at 1 kHz to 60 dB at 9 kHz. The slope is (60-20)/(9-1) = 5 dB/kHz. At 5 kHz, the threshold is 20 + (5 * 4) = 40 dB. The difference between 40 dB and 20 dB is 20 dB, which corresponds to a factor of 10^(20/10) = 100.

$I = \dfrac{Power}{Surface Area}$

The intensity of sound in decibel is given by: 

Loudness $\beta=10\;log _{10}\displaystyle\frac{I}{I _0}$

$\therefore\;\beta _2-\beta _1=10\;log _{10}\displaystyle\frac{I _2}{I _1}$

$\because\;I=\displaystyle\frac{P}{4\pi r^2}\;\therefore\;\displaystyle\frac{I _2}{I _1}=\displaystyle\frac{r _1^2}{r _2^2}$

$\therefore\;(\beta+20)-\beta=10\;log _{10}\displaystyle\frac{r^2}{r _2^2}=20\;log _{10}\displaystyle\frac{r}{r _2}$

$\Rightarrow \displaystyle\frac{r}{r _2}=10\Rightarrow r _2=0.1\;r$

$\therefore\;shift=r-0.1\;r=0.9\;r$.

The human ear can detect a wide range of frequencies, from the low rumbles of distant thunder to the high-pitched whine of a mosquito. The sensory cells that detect these sounds are called hair cells, named for the hair-like strands that cluster on their tops. Hair cells are spread across a flat surface called the basilar membrane, which is rolled like a carpet and tucked into a snail shell-shaped structure in the inner ear called the cochlea. Each of our roughly 16,000 hair cells is dedicated to a narrow frequency range. These cells are ordered along the basilar membrane according to the frequencies they detect.

The amplitude is the SI unit of the pitch of the sound. So, the correct option is "Amplitude".

The standard range of human hearing is generally cited as 20 Hz to 20,000 Hz. Option C (50 Hz to 15,000 Hz) is the closest acceptable range provided in the options.

The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz. Although hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear, human deafness most commonly occurs because of abnormalities of the inner ear, rather than in the nerves or tracts of the central auditory system. Sound below 20 Hz is considered infrasonic, which the ear cannot process. Therefore, the correct answer is option A.

• When sound waves from the environment enter the external ear, they are directed to ear drum (tympanic membrane). 
• The ear drum vibrates on receiving sound waves and the vibrations are sent to oval window through ear ossicles which are malleus, incus and stapes. 
• From the oval window, these vibrations are passed onto fluid of cochlea where waves are generated into lymph due to these vibrations. 
• These waves generate vibrations in the basilar membrane which bend the hair cells and press them against the tectorial membrane.
• This results in the generation of nerve impulses in afferent neurons which are transmitted by afferent fibres to auditory cortex of brain. 
• The impulses are analysed and recognised in brain.

• Sound waves from the environment enter the external ear and are directed to ear drum (tympanic membrane). 
• The ear drum vibrates on receiving sound waves and the vibrations are sent to oval window through ear ossicles which are malleus, incus and stapes. 
• From the oval window, these vibrations are passed onto fluid of cochlea where waves are generated into lymph due to these vibrations. 
• These waves generate vibrations in the basilar membrane which bend the hair cells and press them against the tectorial membrane.

Within the bony labyrinth, is the membranous labyrinth; filled with the fluid called as endolymph. The membranous labyrinth within the cochlea contains the organ of Corti containing the inner and outer hair cells, that generate the nerve impulses required for hearing. Nerve impulses generated in the inner ear travel along the vestibulocochlear nerve (cranial nerve VIII) to the brain.