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Question 1
ప్రశ్న 1
A municipal pumping station is causing repeated noise complaints at nearby houses. Which control strategy best follows the source-path-receiver hierarchy?
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Explanation:
Noise control should begin with identifying the dominant sound sources and their operating conditions. Correcting the source can benefit several exposed locations at once. Enclosures and barriers can then interrupt the airborne transmission path. Receiver-side protection may supplement these engineering measures when necessary. Relocating a measuring instrument or providing occupational ear protectors alone does not control neighbourhood noise.
వివరణ:
Question 2
ప్రశ్న 2
A centrifugal pump develops increasing tonal noise after prolonged operation, accompanied by bearing wear and shaft misalignment. Which intervention most directly addresses a likely source mechanism?
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Explanation:
Worn bearings and misalignment can produce mechanical vibration and tonal noise. Maintenance and alignment target these noise-generating mechanisms at source. Rigid connections may transmit vibration to additional radiating surfaces. A distant barrier would not correct a deteriorating machine. Follow-up measurements are needed to confirm the actual noise reduction after repair.
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Question 3
ప్రశ్న 3
A ventilation system requires the same airflow but produces excessive aerodynamic noise near its fan. Which proposal should be examined as a source-control measure?
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Explanation:
Fan noise depends on operating speed, aerodynamics and surrounding duct conditions. A suitable larger or better-designed fan may deliver the required duty at a lower speed. Smooth duct transitions can also reduce turbulence-related noise. Any replacement must still satisfy flow and pressure requirements. The design should be verified for energy use, vibration and measured noise performance.
వివరణ:
Question 4
ప్రశ్న 4
Airborne noise escapes from a municipal diesel-generator exhaust outlet. Which device-principle pairing is most suitable for basic engineering evaluation?
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Explanation:
Exhaust systems can carry strong airborne acoustic energy from combustion machinery. A suitable silencer attenuates sound propagating through the exhaust passage. Reactive and dissipative principles may be used depending on the frequency spectrum. The device must be compatible with temperature, gas flow and allowable back-pressure. Measurement instruments can assess performance but do not themselves silence an exhaust.
వివరణ:
Question 5
ప్రశ్న 5
A generator installed on a rigid slab causes vibration and low-frequency noise in an adjoining building through connected pipework. Which intervention most directly targets structure-borne transmission?
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Explanation:
Structure-borne noise can arise when machine vibration travels through foundations or rigid pipes. Properly designed isolators reduce transmission of dynamic forces. Flexible connectors can interrupt additional vibration paths. Mount stiffness, supported mass and operating frequencies must be checked to avoid amplification near resonance. Acoustic room treatment alone does not eliminate rigid mechanical transmission.
వివరణ:
Question 6
ప్రశ్న 6
Consider two statements about resilient isolation of a steadily vibrating machine: I. Isolation performance depends on the ratio of forcing frequency to the mounted system's natural frequency. II. Any resilient mount necessarily reduces transmitted vibration at every operating frequency. Which option is correct?
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Explanation:
A mounted machine and its supports form a dynamic system with one or more natural frequencies. The frequency ratio is central to its vibration-transmission behaviour. Near resonance, transmitted vibration may be amplified rather than reduced. Proper isolator selection therefore requires information about operating speed, loading and damping. A flexible support cannot be assumed beneficial at every excitation frequency.
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Question 7
ప్రశ్న 7
An acoustically hard pump-room ceiling produces strong reverberation, while a neighbouring office requires reduced transmission through a common wall. Which distinction between treatments is correct?
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Explanation:
Absorptive finishes reduce the buildup of reflected sound in reverberant spaces. Blocking sound from one room to another instead requires adequate transmission loss and control of openings. A lightweight porous lining may absorb sound without providing effective isolation. Room absorption alone does not eliminate a direct sound path to a receiver. The best design may combine absorptive treatment with a suitable sealed partition.
వివరణ:
Question 8
ప్రశ్న 8
A wastewater-treatment blower is fitted with an acoustic enclosure, but the measured reduction is much less than predicted. Which defect and remedy should be considered first?
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Explanation:
A high-performing panel can be undermined by an unsealed gap or untreated opening. Sound escaping through leaks may dominate the residual level outside an enclosure. Doors, penetrations and ventilation paths need appropriate acoustic treatment. Cooling, maintenance access and fire safety must still be maintained. Overall enclosure performance cannot be inferred from wall material alone.
వివరణ:
Question 9
ప్రశ్న 9
A roadside noise barrier shields single-storey houses but produces little benefit for upper-floor windows overlooking the road. Which mechanism best explains this outcome?
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Explanation:
An outdoor barrier works mainly by interrupting sound propagation from source to receiver. Sound can still diffract over the barrier top and around its ends. Elevated receivers may lie outside the effective acoustic shadow. Increasing barrier height or changing alignment may improve performance in suitable cases. Barrier evaluation must consider receiver height, length, gaps and other site constraints.
వివరణ:
Question 10
ప్రశ్న 10
Houses near the end of a proposed highway noise barrier remain strongly exposed even though the wall blocks the direct road view in front of them. Which modification is most relevant?
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Explanation:
Noise barriers can lose effectiveness when sound travels around an inadequately extended end. A wall may block the direct path in one direction while leaving a short lateral route. Extending its length can improve shielding of affected receivers. The correct extension depends on roadway and receiver geometry. Access, safety and cost must also be assessed during final design.
వివరణ:
Question 11
ప్రశ్న 11
Two tall, approximately parallel roadside walls are planned along a traffic corridor, and repeated reflections could reduce their acoustic effectiveness. Which design response is best supported?
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Explanation:
Parallel reflective surfaces can redirect sound back and forth across a corridor. These reflections may influence the net insertion loss of a barrier system. Absorptive facing materials can reduce some reflected energy. The spacing, height and location of the walls also influence the result. The final design should evaluate receiver-specific acoustic performance rather than assuming that all reflections are harmless.
వివరణ:
Question 12
ప్రశ్న 12
A new residential township is proposed next to a major traffic corridor. Which planning measure best integrates prevention of future environmental-noise exposure?
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Explanation:
Land-use planning can reduce exposure before new sensitive receptors are occupied. Setbacks and compatible land-use buffers separate some sources from homes and schools. Building orientation and suitable barriers can provide additional mitigation. Vegetation may have amenity benefits but should not be assigned a universal large acoustic attenuation. The chosen measures should be evaluated using realistic source and receiver conditions.
వివరణ:
Question 13
ప్రశ్న 13
A resident near a noisy roadway proposes double-glazed, well-sealed windows to improve indoor conditions. Which statement best distinguishes receiver protection from community ambient-noise compliance?
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Explanation:
Windows and facade constructions can reduce sound entering an occupied room. Their effectiveness depends on glazing, seals, ventilation and flanking paths. Such treatment protects the indoor receiver rather than eliminating the roadway emission. Outdoor regulatory noise measurements remain distinct from indoor comfort measurements. Receiver protection can complement, but not automatically replace, community noise controls.
వివరణ:
Question 14
ప్రశ్న 14
A municipality must limit noise from night roadworks near housing. Which combined plan is most appropriate for engineering evaluation?
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Explanation:
Construction noise comes from engines, impact tools, handling activities and vehicle movement. Source maintenance and operating practices can reduce avoidable noise generation. Temporary shields and activity scheduling can further limit receptor exposure. Worker protection remains important but does not replace community controls. Monitoring should cover representative noisy activities and the times when sensitive receptors are affected.
వివరణ:
Question 15
ప్రశ్న 15
Consider ideal outdoor geometrical spreading: I. The sound level from a compact point source decreases by approximately 6 dB for each doubling of distance in a free field. II. An ideal long, continuous line source decreases by approximately 3 dB for each doubling of perpendicular distance. Which option is correct?
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Explanation:
An ideal point source produces approximately spherical spreading in a free field. Its intensity therefore falls approximately with the inverse square of distance. A sufficiently long uniform line source produces approximately cylindrical spreading under ideal conditions. This leads to about 3 dB of reduction per distance doubling instead of 6 dB. Real traffic corridors may differ because of finite lengths, ground effects, reflections and meteorology.
వివరణ:
Question 16
ప్రశ్న 16
A compact stationary pump behaves as an ideal point source in a free field and produces 84 dB(A) at a distance of 10 m. Ignoring reflections and atmospheric absorption, what level is expected at 40 m?
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Explanation:
For an ideal point source, level difference is 20 times the logarithm of the distance ratio. The receiver distance increases from 10 m to 40 m, a factor of four. Geometrical spreading therefore reduces the level by 20 log10(4), approximately 12.04 dB. The predicted level is 84 minus 12.04, or about 72 dB(A). Site reflections and barriers are excluded by the stated assumptions.
వివరణ:
Question 17
ప్రశ్న 17
An ideal indefinitely long, uniformly emitting roadway is modelled as a line source with 75 dB(A) at a perpendicular distance of 20 m. What level is predicted at 80 m if only cylindrical geometrical spreading occurs?
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Explanation:
An ideal long line source follows cylindrical spreading under the question's assumptions. Its level change is 10 times the logarithm of the distance ratio. The distance increases by a factor of four, from 20 m to 80 m. Attenuation is 10 log10(4), approximately 6.02 dB. The resulting level is 75 minus 6.02, or approximately 69 dB(A).
వివరణ:
Question 18
ప్రశ్న 18
Under comparable traffic and weather conditions, an outdoor receiver measures 77 dB(A) before and 69 dB(A) after a noise barrier is installed. What are the observed insertion loss and approximate remaining sound-energy fraction at that receiver?
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Explanation:
The observed insertion loss is the before-minus-after level difference under comparable conditions. It equals 77 minus 69 = 8 dB. The ratio of remaining to initial acoustic energy is 10 raised to negative 8/10. This equals approximately 0.158, or 15.8%. The reduction applies to the observed receiver level and is not a universal performance rating for the same barrier at other locations.
వివరణ:
Question 19
ప్రశ్న 19
Two independent, incoherent machines each contribute 70 dB(A) at a receptor. Maintenance lowers only the first machine to 60 dB(A), with the second unchanged. Approximately how much does the combined receptor level decrease?
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Explanation:
Two independent equal 70 dB(A) sources combine to approximately 73.01 dB(A). After maintenance, the energy terms correspond to 60 and 70 dB(A). Their logarithmic sum is 10 log10(10^6 + 10^7), approximately 70.41 dB(A). The combined level therefore falls by about 73.01 minus 70.41 = 2.60 dB. Treating the 10 dB change in one source as a 10 dB change in the total would neglect the unchanged second machine.
వివరణ:
Question 20
ప్రశ్న 20
A receiver experiences a steady 72 dB(A) background from other sources and 80 dB(A) from a particular blower, with incoherent contributions. A silencer lowers only the blower contribution to 70 dB(A). What are the approximate combined levels before and after the silencer?
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Explanation:
The initial total is the logarithmic sum of 80 and 72 dB(A). This gives 10 log10(10^8 + 10^7.2), approximately 80.64 dB(A). After silencing, the corresponding contributions are 70 and 72 dB(A). Their logarithmic sum is approximately 74.12 dB(A). The overall reduction is about 6.52 dB because the unchanged background limits the benefit of controlling only one source.
వివరణ:
Question 21
ప్రశ్న 21
During an eight-hour residential nighttime assessment, the receiver experiences 60 dB(A) for one hour and 45 dB(A) for seven hours. If a future control is assumed to reduce the resulting nighttime LAeq uniformly without changing durations, approximately what reduction is needed to reach the Indian residential nighttime numerical limit of 45 dB(A) Leq?
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Explanation:
Equivalent continuous sound level uses an energy-weighted average over the assessment period. The mean energy term is (10^6 + 7 times 10^4.5)/8. Taking ten times its base-10 logarithm gives approximately 51.84 dB(A). The residential nighttime limit is 45 dB(A) Leq under the applicable Indian rules. The assumed uniform reduction must therefore be about 51.84 minus 45 = 6.84 dB, or approximately 6.8 dB.
వివరణ:
Question 22
ప్రశ్న 22
A blower produces 78 dB(A) at an affected receiver. A source treatment is demonstrated to reduce that same sound path by 8 dB, and a downstream path treatment provides another 5 dB, with no significant flanking transmission or other source contributions. What is the final receiver level?
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Explanation:
The initial receiver level is 78 dB(A). The first treatment decreases the level by 8 dB, leaving 70 dB(A). The second treatment acts on the same remaining sound path and reduces it by a further 5 dB. With negligible bypass paths or other contributions, the reductions can be combined on the decibel scale as 13 dB. The predicted final receiver level is 78 minus 13 = 65 dB(A).
వివరణ:
Question 23
ప్రశ్న 23
A 30 m2 room surface has a sound-absorption coefficient of 0.20 before treatment and 0.70 after acoustic treatment, for a specified frequency band. What is the increase in its equivalent sound-absorption area?
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Explanation:
Equivalent sound-absorption area is surface area multiplied by the absorption coefficient. Before treatment, the surface contributes 30 times 0.20 = 6 m2 sabin. After treatment, it contributes 30 times 0.70 = 21 m2 sabin. The increase is therefore 21 minus 6 = 15 m2 sabin. This quantity represents absorption and should not be interpreted as the sound transmission loss of the separating wall.
వివరణ:
Question 24
ప్రశ్న 24
For an ideal undamped single-degree-of-freedom vibration isolator, force transmissibility is T = 1/|1 - r^2|, where r is excitation frequency divided by mounted natural frequency. A machine operates at 24 Hz on supports with natural frequency 8 Hz. What is the predicted transmitted-force amplitude as a percentage of the exciting-force amplitude?
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Explanation:
The frequency ratio is r = 24/8 = 3. The specified undamped transmissibility formula then gives T = 1/|1 - 9|. This is 1/8, or 0.125. Therefore the predicted transmitted-force amplitude is 12.5% of the exciting-force amplitude. Actual isolators have damping and additional modes, so this is an idealized calculation rather than a guaranteed field result.
వివరణ:
Question 25
ప్రశ్న 25
A residential receptor has 68 dB(A) LAeq during the daytime, dominated by one ventilation source. A verified modification reduces the source's contribution at that receiver by 7 dB, and an additional barrier is predicted to reduce the remaining path level by 6 dB; assume other sources and flanking paths are negligible. How does the final level compare with the Indian residential daytime numerical limit?
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Explanation:
The question states that both improvements act sequentially on the dominant source at the receiver. Their level reductions therefore total 7 + 6 = 13 dB under the stated negligible-bypass assumption. The predicted receiver level is 68 minus 13 = 55 dB(A). The Indian residential daytime ambient standard is 55 dB(A) Leq. The scenario therefore meets the numerical daytime limit at equality, while real compliance would still require representative measurement and appropriate assessment.
వివరణ:
Answer Key సమాధానాల పట్టిక
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Question 1 ప్రశ్న 1Answer: B. Investigate and reduce pump and motor noise at source first, then use enclosures or path controls and appropriate receiver protection if needed. సమాధానం: B.
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Question 2 ప్రశ్న 2Answer: D. Inspect and repair bearings, restore alignment and balance, and verify the result by repeat noise and vibration measurements. సమాధానం: D.
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Question 3 ప్రశ్న 3Answer: A. Select a suitably designed lower-speed fan with appropriate blade and duct geometry while maintaining the required airflow and pressure. సమాధానం: A.
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Question 4 ప్రశ్న 4Answer: C. A suitably rated exhaust silencer that attenuates sound propagating in the gas path while maintaining acceptable back-pressure. సమాధానం: C.
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Question 5 ప్రశ్న 5Answer: A. Use correctly selected resilient machine mounts and flexible pipe connectors while checking stability and operating-frequency compatibility. సమాధానం: A.
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Question 6 ప్రశ్న 6Answer: D. Only I is correct. సమాధానం: D.
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Question 7 ప్రశ్న 7Answer: B. Porous treatment can reduce reflected sound within the room, while an adequately sealed, sound-insulating partition primarily resists transmission into the office. సమాధానం: B.
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Question 8 ప్రశ్న 8Answer: C. Unsealed doors, cable penetrations or unattenuated ventilation openings may allow sound leakage; seal or acoustically treat these paths while maintaining cooling and access. సమాధానం: C.
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Question 9 ప్రశ్న 9Answer: D. Upper-floor receivers may retain a direct line of sight or receive more diffracted sound over the top, so barrier geometry and receiver elevation must be assessed. సమాధానం: D.
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Question 10 ప్రశ్న 10Answer: A. Evaluate extending the barrier or adjusting its alignment to reduce sound diffracting around the exposed end. సమాధానం: A.
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Question 11 ప్రశ్న 11Answer: C. Evaluate sound-absorptive treatments on relevant faces and the corridor geometry to limit adverse multiple reflections. సమాధానం: C.
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Question 12 ప్రశ్న 12Answer: B. Use suitable setbacks, land-use buffers, building orientation and, where justified, engineered barriers or facade measures based on predicted receiver levels. సమాధానం: B.
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Question 13 ప్రశ్న 13Answer: D. Suitable facade insulation can reduce indoor transmitted sound but does not by itself reduce the outdoor ambient level or establish compliance with an outdoor noise limit. సమాధానం: D.
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Question 14 ప్రశ్న 14Answer: A. Use appropriately maintained low-noise equipment, avoid unnecessary idling and impacts, consider feasible temporary barriers and scheduling restrictions, and verify noise at affected receivers. సమాధానం: A.
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Question 15 ప్రశ్న 15Answer: C. Both statements I and II. సమాధానం: C.
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Question 16 ప్రశ్న 16Answer: B. Approximately 72 dB(A). సమాధానం: B.
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Question 17 ప్రశ్న 17Answer: D. Approximately 69 dB(A). సమాధానం: D.
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Question 18 ప్రశ్న 18Answer: A. 8 dB and about 15.8% remaining. సమాధానం: A.
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Question 19 ప్రశ్న 19Answer: C. 2.6 dB. సమాధానం: C.
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Question 20 ప్రశ్న 20Answer: B. 80.6 and 74.1 dB(A). సమాధానం: B.
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Question 21 ప్రశ్న 21Answer: D. 6.8 dB. సమాధానం: D.
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Question 22 ప్రశ్న 22Answer: A. 65 dB(A). సమాధానం: A.
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Question 23 ప్రశ్న 23Answer: C. 15 m2 sabin. సమాధానం: C.
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Question 24 ప్రశ్న 24Answer: B. 12.5%. సమాధానం: B.
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Question 25 ప్రశ్న 25Answer: A. The final level is 55 dB(A), equal to the residential daytime limit. సమాధానం: A.