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The correct answer is (c) Q = 640 C.A. [h(T-t)]^½

To explain: The rate of flow of air arising due to the difference in temperature of OUTSIDE and inside is given by the expression Q = 640 C.A. [h(T-t)]^½. Here, C stands for coefficient of EFFECTIVENESS, Q is the rate of air flow in m^3/h, A is the FREE area of the INLET opening, h is the vertical height difference between inlet and outlet, T is the AVERAGE temperature of inside air and t is the average temperature of outside air in degree Celcius.

Correct OPTION is (d) TWO leeward faces

Explanation: If the direction of the wind is at 45° to ONE of the faces, NEGATIVE pressure will be produced on two leeward faces. Negative pressure will be produced on one leeward face if the direction of the wind is at 90° to one of the faces.

Right option is (a) Windward face

To elaborate: If the direction of the WIND is at 90° to ONE of the faces, positive PRESSURE will be produced on the windward face. Positive pressure will be produced on TWO windward faces if the direction of the wind is at 45° to one of the faces.

Right choice is (c) Loudness

For EXPLANATION: The intensity of sound and loudness are totally DIFFERENT terms. The intensity of sound is purely physical quantity WHEREAS loudness is not wholly physical, but partly subjective and it does DEPEND on the ear of LISTENER.

Correct answer is (b) 6 m

The best I can explain: The average HEIGHT for small halls should be 6 m while the average height for large halls should be 7.5 m. The height is determined by various FACTORS such as ventilation, PRESENCE of balcony, TYPE of performance etc.

Correct choice is (d) 17 m

To explain: The formation of ECHOES can take place when the reflecting surfaces are LOCATED at a distance greater than 17m. This defect can be removed by making surfaces highly ABSORBENT.

The correct CHOICE is (c) Speed

Explanation: There are three CHARACTERISTICS of sound. These are INTENSITY and loudness, FREQUENCY and pitch, and quality or timbre.

Correct choice is (d) 60 per HOUR

The BEST I can explain: Air change per hour is defined as the volume of OUTSIDE air ALLOWED in a room per hour as compared to the volume of the room. The maximum RATE of air change is 60 per hour while the minimum rate of air change is 1 per hour.

Right OPTION is (B) 0.65

Easiest EXPLANATION: In the expression for finding the rate of flow of AIR ARISING due to the difference in temperature of outside and inside, coefficient of effectiveness for general conditions is taken as 0.65. However, it is taken as 0.50 in the case of unfavorable conditions.

Correct answer is (C) Q = AV/K

Explanation: The rate of FLOW through an opening due to the WIND blowing on the wall containing it is given by the expression where Q = rate of air flow in m^3/h, A = area of the smaller opening in SQUARE metres, K is the coefficient of effectiveness and V is the wind speed in m/h.

Correct answer is (c) Natural ventilation

For explanation I would say: Natural ventilation is USEFUL for small buildings and it cannot be adopted for big offices, theatres, AUDITORIUMS, etc. The only ADVANTAGE of the system is that it is economical in the sense that no special equipment is necessary for making the room adequately ventilated and that is affords living under natural conditions.

The correct option is (d) REVERBERATION

The explanation: The defect of excessive reverberation is very common in many auditoriums. The effect is that the SOUND once created prolonged for a longer duration resulting in confusion with the sound created next. The REMEDY of this defect is to correct the TIME of reverberation by suitably installing the absorbent materials.

The CORRECT option is (C) to hear

Easy explanation: Hence, the Acoustic is DEFINED as the science of SOUND and as such, discusses the origin, propagation and auditory SENSATION of sound.

Correct choice is (d) Concave reflecting

Easy explanation: SOUND foci is a defect CAUSED by concave reflecting interior surfaces. It is because of the concentration of the REFLECTED sound WAVES at certain spots. This defect can be removed by avoiding curvilinear interiors.

Right CHOICE is (b) False

To explain: SOUND waves reflected at a concave surface are diminished while the sound waves reflected at convex surfaces are large and magnified. A convex surface is used to spread the sound waves throughout the room and a concave surface is used for the CONCENTRATION of reflected waves at certain POINTS.

Correct CHOICE is (a) Pitch of the sound increases with increase in frequency

Easy explanation: Pitch of the sound increases with an increase in frequency. Decibel is equal to 1/10 of BEL. An increase in the amplitude of the sound increases the INTENSITY.

The correct answer is (a) 0.5 MG

To explain I would say: Clean air should contain less than 0.5 mg of suspended impurity per cubic METRE. Also, it should have less than 0.5 part per MILLION of SO₂. Air should be free from toxic FUMES of gases and harmful particles.

The correct answer is (d) 45-56 cm

The best I can explain: The seats in an auditorium should be arranged in CONCENTRIC ARCS of circles drawn with the centre situated as much BEHIND the centre of the curtain LINE as its distance is from the rear wall of the auditorium. The width of the seats in an auditorium should be between 45-56 cm.

Right answer is (c) Artificial ventilation

To EXPLAIN: Mechanical or Artificial ventilation has become popular due to recent change in notion regarding ventilation. At present, the ventilation is required not nearly to furnish warm air or COOL air. But the ventilation system should PROVIDE air of such qualities regarding humidity, TEMPERATURE, etc.

The correct option is (b) DEAD spots

To explain: The sound LEVEL and at dead spots is generally inadequate for satisfactory hearing. This defect can be remedied by the installation of the SUITABLE diffuser so as to have even DISTRIBUTION of sound in the hall.

Correct answer is (d) Viscous FILTERS

Best explanation: The viscous filters maybe of unit TYPE or automatic type. In the FORMER type, the Mats are replaced when they become dirty or they are WASHED and recoiled. In the latter type, an endless CHAIN moving over the mats is provided.

The correct option is (a) 340 m/s

Explanation: The wavelength of sound i.e. the PHYSICAL distance in air from ONE wave top to the next can be found out by knowing its speed and frequency with the HELP of formula or equation. For acoustics and sound MEASUREMENT purposes, the speed of sound is taken as 340 m/s.

Correct option is (b) 2:3:5

Explanation: In the acoustical design of a studio, the ratio of HEIGHT, breadth and length of the studio should be 2:3:5. The WALLS of the studio should be of rigid CONSTRUCTION in ORDER to insulate the external noise COMPLETELY.

The correct choice is (c) Non-rigid porous materials

Best explanation: FELT and mineral wool are examples of non-rigid porous materials. These materials are not USUALLY USED for the purpose of noise reduction because the SOUND insulation provided by them is LOW as compared to the rigid materials.

Right choice is (C) 3.5-4.5 m^3 PER person

Explanation: The recommended volume for a public lecture hall is 3.5-4.5 m^3 per person. While the volume recommended for cinemas is 4.0-5.0 m^3 per person and that for MUSICAL HALLS is 4.0-5.5 m^3 per person.

The correct choice is (a) True

The explanation is: ECHOES are formed due to the unsuitable shape of the hall/auditorium. HENCE, the PROPER shape of the hall can HELP in preventing the formation of echoes.

Correct CHOICE is (d) 4300 m/sec

Explanation: The VELOCITY of SOUND in AIR at 20°C is 343 m/sec. The velocity of sound in bricks is 4300 m/sec while that in concrete is 4000 m/sec.

Correct ANSWER is (d) ELECTRIC precipitator

To explain: The initial cost of electric precipitators is high, but the operation cost is low. A strong electric field is developed and DUST particles are subjected to this electric field are ATTRACTED TOWARDS negative electrode. The sufficient quantity of dust particles deposited on the negative electrode is removed at intervals.

The correct answer is (d) Exhaust

For explanation I would say: In exhaust system, the extraction of air from inside sets of the CURRENT of fresh air from outside to inside and THUS, it becomes possible to provide fresh air to the room through doors and windows. The fans or blowers are installed at suitable places in the outside wall and they are CONNECTED to different ROOMS through DUCT system.

The CORRECT option is (C) Reverberation

To explain: As a MATTER of fact, the acoustic design of an Auditorium will be incomplete without the provision of reverberation. The careful study of the hall should be MADE before recommending the type of absorbent material and its location in the hall.

The correct CHOICE is (c) STUDIO

To explain: The basic requirements of a studio will be to have perfect soundproofing and to have variable reverberation time as per nature of sound produced in it. The acoustic design of a studio require SPECIAL precaution to be undertaken for its effective WORKING.

The correct option is (a) Exterior noise

The BEST explanation: The exterior noise enters the Auditorium either through loose doors and windows on walls and other structural ELEMENTS having in proper sound insulation. The exterior noise is developed by vehicles, FACTORIES, cooling PLANTS, etc. The remedy to correct this DEFECT is to provide suitable sound insulation.

Right option is (c) 50 dB

Best explanation: In rigid homogeneous WALLS, the transmission loss of a one-brick wall is 50 dB. The transmission loss of a one and a half brick thick wall is 53 dB and that of a half brick thick wall having 13 mm thick plaster on both SIDES is 45 dB.

Right option is (B) False

To elaborate: For lecture HALLS, small volumes are beneficial for weak sounds. However, for MUSIC halls, the VOLUME should be large in order to have enough SPACE for the music to spread in the hall.

Right choice is (c) Square

Best explanation: Intensity is the amount of wave energy passing through a unit area PER unit TIME. The area TAKEN is PERPENDICULAR to the direction of the propagation of the wave. The intensity of sound is proportional to the square of the amplitude.

The CORRECT answer is (b) 194.4 m^3/h

To explain: The flow through an OPENING is given by the expression Q = K.A.V. Therefore, the flow of air through two square OPENINGS of SIZE 0.36 m with the wind blowing at a speed of 5 km/h is 0.3 x 0.36 x 0.36 x 5000 = 194.4 m^3/h.

Correct choice is (d) Effective temperature

To explain I would say: Effective temperature indicates the temperature of air at which sensation of same degree of COLD or warmth will be experienced as in QUITE a FULLY saturated at the same temperature. Thus, if two rooms have the same effective temperature, no change of temperature will be experienced by a person when he suddenly leaves ONE room and enters the room.

The correct answer is (a) Sound FOCI

Easiest EXPLANATION: Sound foci is observed where reflected sound wave MEET and create a sound of larger intensity. This defect can be eliminated by avoiding curvilinear interiors or by providing highly absorbent materials on the focusing areas.

The correct choice is (c) Echoes

Easy explanation: When the reflecting SURFACES are situated at a distance GREATER than 17 meters or so and when the shape of the AUDITORIUM is unsuitable, the formation of echoes takes place. This defect can be removed by SELECTING proper shape of the Auditorium and by providing rough and porous interior surfaces to DISPERSE the energy of a Echoes.

Right choice is (a) IMPACT

To explain: CONCRETE floor floating construction provides good INSULATION against impact sounds. In this type of construction, an additional floor is CONSTRUCTED and isolated from the already EXISTING concrete floor.

Correct option is (a) Porous materials

Easiest explanation: Absorbents are BROADLY classified as porous materials, resonant PANELS, cavity RESONATORS and COMPOSITE types. Rock wool is an example of porous material. Other EXAMPLES of porous materials are glass wool, wood wool, etc.

Correct option is (d) Weber and Fechner’s law

For EXPLANATION I WOULD SAY: Weber and Fechner’s law states that the MAGNITUDE of a sensation is directly proportional to the logarithm of the physical stimulus producing it. For example, loudness which corresponds to the magnitude of the sensation is proportional to the logarithm of the intensity of the sound.

The correct choice is (b) False

Explanation: A sound wave is a longitudinal wave. Sound is transmitted in the FORM of these longitudinal waves which are a SERIES of compressions and rarefactions CREATED in the medium through which the sound propagates. The velocity of the sound depends on the medium through which it travels. Sound travels faster in SOLIDS than in gases.

The correct answer is (d) 8°C

The best I can explain: The general temperature difference between inside and outside of a ROOM is not more than 8°C. It is PREFERABLE that the incoming VENTILATING air should be WARM in winters and COOL in summers.