Physics Questions for Railway & SSC CGL Exam 2018 : 12th June


SOUND:

Dear Students,

Railway Board offers opulent and revered job posts to its aspirants. And it is not every year that we get the notification from Railway offering a good number of vacant seats to the multitude aspirants. But the current year 2018 brought a pleasant surprise with almost 90,000 seats to be filled by the valid candidates. Opportunity is here but you have to welcome it with a provident strategy. The exam will be conducted in the months of May 2018. 

रेलवे बोर्ड अपने उम्मीदवारों के लिए भव्य और प्रतिष्ठित कार्य पदों की पेशकश करता है. और हर साल ऐसा नहीं होता है कि हमें रेलवे की ओर से अधिसूचना मिलती है. लेकिन वर्तमान वर्ष 2018 आपके लिए बहुत सुखद वर्ष है क्योंकि इसमें लगभग 90,000 सीटों को वैध उम्मीदवारों द्वारा भरा जाएगा. आपके पास बहुत अच्छा अवसर है और आपको इसे एक बेहतर रणनीति से प्राप्त करना होगा. परीक्षा मई 2018 के महीने में आयोजित की जायेगी.

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Q1. Put in ascending order of speed of sound in the mediums I-Water, II-Steel, III-Nitrogen- 
निम्नलिखित माध्यम I-जल , II-स्टील , III- नाइट्रोजन-में ध्वनि की गति को आरोही क्रम में व्यवस्थित करें.
(a) III, II, I
(b) III, I, II
(c) I, III, II
(d) II, I, III
Show Answer
Ans.(b)
Sol. The speed of sound is different for different type of mediums. The speed of sound is maximum in solids while minimum in gases. The speed of sound in air at normal temperature and pressure is 322m/s. The speed of sound depends on the density of the medium through which it is travelling. The medium which has higher density, the sound will travel faster in that medium.

Q2. In which medium the speed of sound is maximum at a temperature of around 20°C? 
किस माध्यम में ध्वनि की गति अधिकतम 20 डिग्री सेल्सियस के तापमान पर अधिकतम होती है?
(a) Air  / वायु
(b) Granite / ग्रेनाइट
(c) Water  / जल
(d) Iron  / लौहा
Show Answer
Ans.(d)
Sol. The speed of sound depends on the elasticity and density of the medium through which it is travelling. Greater the elasticity and lower the density, sound travels faster in that medium. At temperature of 20°C, the speed of sound is maximum in iron.


Q3. Sound waves- 
ध्वनि तरंगे- 
(a) Can travel in vacuum/ वैक्यूम में यात्रा कर सकती हैं
(b) Can travel only in solids / केवल ठोस में यात्रा कर सकती हैं
(c) Can travel only in gases. / केवल गैसों में यात्रा कर सकती हैं
(d) Can travel both in solid and gaseous medium./ ठोस और गैसीय मध्यम दोनों में यात्रा कर सकती हैं.
Show Answer
Ans.(d)
Sol. Sound waves need to travel through a medium such as a solid, liquid or gas. The sound waves travel through each of these mediums by vibrating the molecules in the matter. The molecules in solids are packed as tightly as solids, and in gases they are very loosely packed. The spacing of the molecules, enable sound to travel much faster through solid than gases, So sound waves can travel in solid, liquid and gaseous medium.

Q4. The walls of the hall, built for music concerts should- 
हॉल की दीवारों, संगीत संगीत कार्यक्रमों के लिए कैसा बनाया जाना चाहिए-
(a) Amplify sound  / परिवर्धित ध्वनि
(b) Transmit sound /  ध्वनि संचार
(c) Reflect sound / प्रतिबिंबित ध्वनि
(d) Absorb sound / अवशोषण ध्वनि
Show Answer
Ans.(d)
Sol. The walls of the hall built for music concerts should absorb sounds. Most of the solid walls reflects the sound. If the walls of concert hall reflect the sound, then audiences hear the echo sound. So to avoid this, there is a need to built soft surface walls.

Q5. To hear a clear echo, the minimum distance between the reflecting surface and the observer should be- 
एक स्पष्ट गूंज/ प्रतिध्वनि सुनने के लिए, प्रतिबिंबित सतह और पर्यवेक्षक के मध्य न्यूनतम दूरी होनी चाहिए-
(a) 165 feet  / 165 फीट
(b) 165 metre / 165 मीटर
(c) 16.5 feet   /16.5 फीट
(d) 16.5 metre  /16.5 मीटर
Show Answer
Ans.(d)
Sol. The repetition of sound produced due to the reflection from a large surface like wall, hill or mountain is called echo. Consider an observer is producing a sound and it gets reflected by an obstacle. The sound travel towards the observer and the observer hear the sound again. Let d be the distance between the observer and the obstacle, v is the sound velocity and t is the time taken by the sound to and fro motion, then the velocity of the sound is given by
V= 2d/t
Velocity of sound is given by, V = 2d/t
Where t = time taken by the sound for to and fro motion.
Substituting t = 1/10 sec, it is minimum time required to distinguish between two sounds
V = velocity of sound = 330 m/sec
at 20° C
then d=Vt/2=1/2 [330×(1/10)]
= 16.5 m


Q6. The velocity of sound in air is approximately- 
वायु में 0 डिग्री सेल्सियस पर ध्वनि की गति लगभग________ होती है.
(a) 10 km/sec. / 10 किमी / सेकंड
(b) 10 mile/min. / 10 मील / मिनट
(c) 330 m/sec.  / 330 मीटर / सेकंड
(d) 3×1010 /sec.  /3 × 1010 / सेकंड
Show Answer
Ans.(c)
Sol. The speed of sound in air is approximately 331.5 m/s at 0 °C or around 1200 km per hour. The speed of sound through air is approximately 343 m/s at normal room temperature, which is at 20 °C.


Q7. Two astronauts cannot hear each other on the moon’s surface, because- 
चंद्रमा की सतह पर दो अंतरिक्ष यात्री एक-दूसरे को नहीं सुन सकते हैं, क्योंकि-
(a) Their ears have stopped working on the moon / उनके कान चंद्रमा पर काम करना बंद कर देते है
(b) No atmosphere on the moon / चंद्रमा पर कोई वातावरण नहीं
(c) They wear special space suits on the moon  / वे चंद्रमा पर विशेष अंतरिक्ष सूट पहनते हैं
(d) The sound travels much more slowly on moon / चंद्रमा पर ध्वनि बहुत धीरे-धीरे यात्रा करती है
Show Answer
Ans.(b)
Sol. In order for sound to propagate from one place to another, it requires a medium or a fluid to move through. The air on the earth allows sound waves to move from one point to another. However, there is vacuum on surface of moon. Thus, there is no sound on the moon. 

Q8. Consider the following statements: 
निम्नलिखित कथनों पर विचार करें:
1. A flute of smaller length produces waves of lower frequency. / एक छोटी लंबाई की बांसुरी कम आवृत्ति की तरंगें पैदा करती है. 
2. Sound travels in rocks in the form of longitudinal elastic waves only. / ध्वनि केवल अनुदैर्ध्य लोचदार तरंगों के रूप में चट्टानों में यात्रा करती है.
Which of the statements given above is/are correct? 
ऊपर दिए गए कथनों में से कौन सा सही है/ हैं?
(a) 1 only / केवल 1
(b) 2 only  / केवल 2
(c) Both 1 and 2 / 1 और 2 दोनों
(d) Neither 1 nor 2 /  ना तो 1 ना ही 2
Show Answer
Ans.(b)
Sol. A flute of long length produces the waves of higher wavelength(λ) and lower frequency(v), thus a flute of smaller length produces waves of higher frequency(v) and lower wavelength(λ) . Therefore statement 1 is not correct. Sound is a longitudinal wave. Transmission of sound in any medium is only possible by longitudinal waves. Thus, sound travels in rocks, in the form of longitudinal wave. Longitudinal waves are the waves in which the displacement of the medium is in the same direction as or the opposite direction to the direction of travel of the wave. Thus statement 2 is correct.

Q9. Consider the following statements about ultrasonic waves: 
अल्ट्रासोनिक तरंगों के बारे में निम्नलिखित कथनों पर विचार करें:
1. They can destroy insects / वे कीड़ों को नष्ट करते है. 
2. They can clean clothes by removing dust /  वे धूल को हटाकर कपड़े साफ कर सकते हैं
3. They can be used to treat disease / वे बीमारी ठीक करने के लिए प्रयोग की जाती है.
4. They can control automatic doors / वे स्वचालित दरवाजों को नियंत्रित करते है.
Of the above statements   
उपरोक्त कथनों में से -
(a) 1 and 2 are correct / 1 और 2 सत्य है
(b) 3 and 4 are correct / 3 और 4 सत्य है
(c) 1, 2 and 3 are correct / 1, 2 और 3 सत्य है
(d) All are correct / सभी सत्य है
Show Answer
Ans.(d)
Sol. Sound waves are longitudinal-mechanical wave. Sound waves are divided into three categories that cover different frequency range; Audible wave (20 Htz- 20,000 Htz), Infrasonic waves (<20Htz) and Ultrasonic waves (>20,000 Htz). Ultrasonic waves are used to destroy insects, clean clothes by removing dust, treat diseases, control automatic doors, detection of aircraft and submarine, determination of depth of sea etc.


Q10. Ultrasonics are sound waves of frequency 
अल्ट्रासोनिक ध्वनि तरंगों की आवृत्ति _________हैं.
(a) Greater than 20,000 Hz  /20,000 हर्ट्ज से अधिक
(b) Less than 10,000 Hz  / 10,000 हर्ट्ज से कम
(c) Equal to 1000 Hz  /1000 हर्ट्ज के बराबर
(d) None of these  / इनमे से कोई नहीं
Show Answer
Ans.(a)
Sol. Sound waves are longitudinal-mechanical wave. Sound waves are divided into three categories that cover different frequency range; Audible wave (20 Htz- 20,000 Htz), Infrasonic waves (<20Htz) and Ultrasonic waves (>20,000 Htz). Ultrasonic waves are used to destroy insects, clean clothes by removing dust, treat diseases, control automatic doors, detection of aircraft and submarine, determination of depth of sea etc.


Q11. A biotechnique in which ultrasonic sound is used-  
एक बायोटेक्निक जिसमें अल्ट्रासोनिक ध्वनि का उपयोग किया जाता है - 
(a) Sonography/सोनोग्राफी
(b) E.C.G / ई.सी.जी
(c) E.E.G / ई.ई.जी.
(d) X-ray/एक्स-रे
Show Answer
Ans.(a)
Sol. Sonography or ultrasonography is an important mean of clinical diagnosis. It is a diagnostic imaging technique based on the application of ultrasound. It is widely used in the field of medical science. It is mainly used to provide a variety of information about the health of the mother during pregnancy, and the health and development of embryo or foetus.

Q12. Bats can fly during dark nights and also prey. This is because- 
चमगादड़ अंधेरी रात के दौरान उड़ सकता है और शिकार भी कर सकता है. क्योंकि - 
(a) The pupil of their eyes is large/उनकी आंखों की पुतली बड़ी होती है
(b) Their night vision is very good/उनकी रात की दृष्टि बहुत अच्छी है
(c) Every birds can do this/हर पक्षी यह कर सकता हैं
(d) They produce ultrasonic waves and are guided by them./वे अल्ट्रासोनिक तरंगों का उत्पादन करते हैं और उनके द्वारा निर्देशित होते हैं.
Show Answer
Ans.(d)
Sol. Bats are a fascinating group of animals. They are one of the few mammals that can use ultrasonic sound to navigate. As they fly, make an ultrasonic (shouting) sound. The returning echoes give the bats information about anything that is ahead of them, including the speed and size of an insect and which way it is going. This system of finding prey is called echolocation-locating things by their echoes.

Q13. Which one of the following is the effect of the flight of supersonic jet? 
निम्नलिखित में से क्या सुपरसोनिक जेट की उड़ान का प्रभाव है?  
(a) Air pollution/वायु प्रदुषण
(b) Eye disease/नेत्र रोग
(c) Depletion in ozone layer/ओजोन परत में कमी
(d) None of these/इनमे से कोई नहीं
Show Answer
Ans.(c)
Sol. A jet engine is a machine for turning fuel into thrust. The thrust is produced by action and reaction also known as Newton’s third law of motion. The force (action) of the exhaust gases pushing backward produces an equal and opposite force (reaction) called thrust, that powers the vehicle forward. Those jet planes which are able to fly faster than the speed of sound are called supersonic jet planes. Jet engines are responsible for depletion of ozone. Flying at stratosphere height, they emits nitrogen oxide which has the potential to destroy significant quantities of ozone in the stratosphere.

Q14. Decibel unit is used to measure- 
डेसीबल  यूनिट किसे मापने के लिए उपयोग किया जाता है -
(a) Light intensity / हल्की तीव्रता
(b) Sound intensity / ध्वनि तीव्रता
(c) Magnitude of Earthquake / भूकंप की तीव्रता
(d) None of the above / उपरोक्त में से कोई नहीं
Show Answer
Ans.(b)
Sol. ‘Decibel’ is used to measure the intensity of sound in atmosphere.


Q15. As per the WHO, the safe noise level for a city is-
WHO के अनुसार, एक शहर के लिए सुरक्षित आवाज़ स्तर कितना है -
(a) 45 db
(b) 50 db
(c) 55 db
(d) 60 db
Show Answer
Ans.(a)
Sol. As per the WHO the safe noise level for a city is 45 decibel (db).






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