Your Answer : (Not Answered)

Correct Answer : C

The correct match is a-iii, b-iv, c-i, d-ii.

The Noise Pollution (Regulation and Control) Rules, 2000 set ambient limits in dB(A) Leq for day and night:

So commercial is 55 (iii), industrial 70 (iv), silent zone 40 (i) and residential 45 (ii). The option with silent zone 45 and residential 40 swaps the two quietest zones. The options giving commercial areas 70 confuse them with industrial areas.

Your Answer : (Not Answered)

Correct Answer : D

The correct match is (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i).

Under the Noise Pollution (Regulation and Control) Rules, 2000, the day-time limits are: industrial area 75 dB(A), commercial area 65 dB(A), residential area 55 dB(A) and silence zone 50 dB(A).

So residential is (iii) 55, silent zone (iv) 50, commercial (ii) 65 and industrial (i) 75. Every other option gives commercial areas 75 dB, the industrial limit, or mixes up residential and silent zones.

Your Answer : (Not Answered)

Correct Answer : C

Vibration sensors work on the piezoelectric effect.

Most vibration sensors are piezoelectric accelerometers. A piezoelectric crystal or ceramic, such as quartz or lead zirconate titanate, produces an electric charge proportional to the force on it, so as the sensor vibrates the mass inside squeezes the crystal and the output voltage follows the acceleration.

Magnetic induction is used in some velocity pickups but is not the standard principle. The photoelectric effect is the basis of light sensors and the thermoelectric effect of thermocouples.

Your Answer : (Not Answered)

Correct Answer : C

Two equal sounds together are 3 dB(A) louder.

Decibels are logarithmic, so sound levels add through their intensities, not directly. Doubling the intensity raises the level by:

\[ \begin{aligned} \Delta L &= 10 \log_{10} \frac{2I}{I} \\ &= 10 \log_{10} 2 \approx 3\ \text{dB} \end{aligned} \]

So 60 dB plus 60 dB gives about 63 dB, not 120 dB. 6 dB is the rise for doubling the sound pressure (or for four equal sources), and 2 and 5 dB match no doubling rule.

Your Answer : (Not Answered)

Correct Answer : B

Normal conversation lies in the range 500 to 2000 Hz.

Most of the energy and intelligibility of human speech falls between about 500 and 2000 Hz, which is why hearing loss in this band, the speech frequencies, is the most disabling and why audiometric assessment focuses on it.

The ranges 10 to 10,000 Hz and 50 to 5000 Hz are far too wide, close to the range of hearing rather than of speech, and 100 to 1000 Hz leaves out the higher frequencies of consonants.

Your Answer : (Not Answered)

Correct Answer : B

The energy transmitted through vacuum is light.

Light is an electromagnetic wave: oscillating electric and magnetic fields that sustain each other and need no medium. That is how sunlight crosses about 150 million km of near-vacuum to reach the Earth.

Sound is a mechanical wave and needs a material medium, so it cannot cross a vacuum. Electric current needs a conductor. Heat can cross a vacuum only as radiation, which is itself electromagnetic, while conduction and convection need matter, so the answer the question wants is light.

Your Answer : (Not Answered)

Correct Answer : A

Both (A) and (R) are true, and (R) is the correct explanation of (A).

Loud noise over-stimulates the sensory hair cells of the cochlea. At first the cells become fatigued and recover, giving a temporary threshold shift; with repeated or prolonged exposure the exhausted hair cells degenerate and die, causing permanent noise-induced hearing loss. Mammalian hair cells do not regenerate.

Since the exhaustion of the hair cells is what leads to their degeneration, the reason explains the assertion.

Your Answer : (Not Answered)

Correct Answer : C

The keyed answer is the tympanic membrane.

Sound waves are collected by the outer ear (the pinna and ear canal; the paper's stem says inner ear). They strike the tympanic membrane, or eardrum, which separates the outer and middle ear and vibrates with them, passing the vibrations into the middle ear.

The tiny bones (malleus, incus and stapes) carry the vibrations across the middle ear on to the inner ear, so they come after the eardrum. The semicircular canals serve balance, and the sensory hair cells of the cochlea in the inner ear turn the vibrations into nerve signals.

Your Answer : (Not Answered)

Correct Answer : C

The wavelength is the distance travelled by sound per cycle.

In one complete cycle of vibration a sound wave advances by one wavelength, the distance between two successive compressions. Speed, frequency and wavelength are linked by

\[ \lambda = \frac{v}{f} \]

so in air (\(v \approx 343\) m/s) a 343 Hz tone has a wavelength of 1 m.

The number of cycles per second is the frequency, and the distance travelled per second is the speed of sound. The distance covered in two cycles is two wavelengths.

Your Answer : (Not Answered)

Correct Answer : B

The speed of sound in air at 0 °C is 331 m/s.

In dry air at 0 °C sound travels at about 331 m/s, increasing by about 0.6 m/s for each degree rise in temperature, so it is about 343 m/s at 20 °C.

The other values belong to other media: about 1,270 m/s is the speed in hydrogen gas, about 1,400 to 1,500 m/s in water, and around 5,000 m/s or more in metals such as iron.

Your Answer : (Not Answered)

Correct Answer : B

Sound travels fastest in solid media.

The speed of sound depends on the stiffness (elastic modulus) of the medium relative to its density. Solids are far stiffer than liquids or gases, so sound moves fastest in them: about 5,000 m/s or more in steel, about 1,500 m/s in water and about 330 to 340 m/s in air.

Liquids come second, and gases and vapours, which are easily compressed, carry sound the slowest.

Your Answer : (Not Answered)

Correct Answer : A

Normal human conversation lies mainly between 500 and 2000 Hertz.

The frequencies that carry most of the information in speech, the speech frequencies, are about 500 to 2000 Hz, which is why hearing tests and noise-induced hearing loss assessments focus on 500, 1000 and 2000 Hz. Human hearing as a whole spans roughly 20 to 20,000 Hz.

The wider bands of 10 to 10,000, 100 to 10,000 and 50 to 5,000 Hz include frequencies far outside the range in which ordinary conversation is concentrated.

Your Answer : (Not Answered)

Correct Answer : C

Permanent hearing loss is due to damage to the Sensory cells.

Loud noise over long periods overstimulates the hair cells of the organ of Corti in the cochlea, which turn sound vibrations into nerve signals. Damaged hair cells do not regenerate in humans, so noise-induced hearing loss is permanent and sensorineural, usually showing first as a dip around 4000 Hz.

The tympanic membrane can be ruptured by a blast, but it usually heals. The malleus, incus and stapes (the ossicles) can be damaged too, giving conductive loss that can often be treated. The semicircular canals control balance, not hearing.

Your Answer : (Not Answered)

Correct Answer : A

The match is a-ii, b-i, c-iv, d-iii.

• 80 dB: annoying, the level of heavy traffic.
• 110 dB: stimulation of reception in the skin, felt as well as heard.
• 120 dB: the threshold of pain.
• 140 dB: pain in the ear, with severe mental disturbance (printed 'insanity').

Two pairings are standard: about 120 dB is the conventional threshold of pain, and 80 dB is merely annoying. Only option A has both a-ii and c-iv.

Your Answer : (Not Answered)

Correct Answer : A

The correct statement is that measurement of sound is a function of electroacoustic method.

A sound level meter works electroacoustically: a microphone converts the pressure fluctuations of sound into an electrical signal, which is amplified, passed through frequency-weighting networks (A, C) and time-weighting circuits, and displayed in decibels. Noise dosimeters and analysers work the same way.

Electrochemical methods measure chemical species, such as dissolved oxygen or gases with electrochemical sensors. 'Biophysical' and 'electrophysical' are not the recognised names of the sound measurement principle.

Your Answer : (Not Answered)

Correct Answer : D

The combined level is 66 dB(A).

Decibels are logarithmic, so sound levels add as energies, not as numbers. For n equal sources each at level L:

\[ \begin{aligned} L_{total} &= L + 10\log_{10} n \\ &= 60 + 10\log_{10} 4 \\ &= 60 + 6.02 \approx 66\ \text{dB(A)} \end{aligned} \]

Each doubling of identical sources adds 3 dB: two machines give 63 dB(A) and four give 66 dB(A). 120 dB(A) is what adding the decibels arithmetically gives for just two machines, and 90 dB(A) also treats the decibel scale as linear; both overstate the increase. 63 dB(A) is the answer for only two machines.

Your Answer : (Not Answered)

Correct Answer : C

The resultant level is 59 dB(A).

Decibels add logarithmically. For n equal sources each of level L:

\[ \begin{aligned} L_{total} &= L + 10\log_{10} n \\ &= 50 + 10\log_{10} 8 \\ &= 50 + 9.03 \approx 59\ \text{dB(A)} \end{aligned} \]

Each doubling of identical sources adds 3 dB: two sources give 53, four give 56 and eight give 59. So 53 and 56 dB(A) are the levels for two and four sources, and 60 dB(A) would need ten.

Your Answer : (Not Answered)

Correct Answer : B

Simple harmonic motion is vibration with a single frequency.

In SHM the restoring force is proportional to the displacement, \(F = -kx\), and the motion is a pure sine curve, \(x = A\sin(\omega t + \phi)\), with one angular frequency \(\omega = \sqrt{k/m}\). It is the most elementary vibration, and any complex periodic vibration can be built from a sum of such single-frequency components (Fourier analysis).

A vibration with two ('Duel') or multiple frequencies is a superposition of several SHMs, not SHM itself, and SHM is continuous and regular, not intermittent.

Your Answer : (Not Answered)

Correct Answer : B

The speed of sound in air at 0°C is about 331 m/s.

The speed of sound in an ideal gas is

\[ v = \sqrt{\frac{\gamma R T}{M}} \]

With \(\gamma = 1.4\), \(R = 8.314\) J/mol K, \(T = 273\) K and \(M = 0.029\) kg/mol for air, this gives about 331 m/s. It rises by roughly 0.6 m/s for each degree, to about 343 m/s at 20°C.

The other figures belong to denser media: around 1,435 to 1,500 m/s is the speed of sound in water, and about 5,100 m/s is typical of iron or steel. 1,269 m/s is far too fast for air.