# RRB ALP Stage-II Exam: Physics Quiz | 17th January

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 last year 2018 brought a pleasant surprise with almost 1,27,278 seats to be filled by the valid candidates. Opportunity is here but you have to welcome it with a provident strategy.

Q1. Surface tension in a liquid is due to :
एक तरल में सतह तनाव किस के कारण होता है?
(a) Adhesive force between molecules/ अणुओं के बीच आसंजक बल
(b) Cohesive force between molecules/ अणुओं के बीच संसक्त बल
(c) Gravitational force between molecules/ अणुओं के बीच गुरुत्वाकर्षण बल
(d) Electrical force between molecules./ अणुओं के बीच विद्युत बल

Ans (b)
Sol. The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension.

Q2. A circular plate, a cube and a sphere, all made up of same material and having the same mass, are heated to 300°C and left in a room. Which of them will have the slowest rate of cooling?
एक गोलाकार प्लेट, एक घन और एक गोला, सभी एक ही सामग्री से बने होते हैं और सबका एक ही द्रव्यमान हैं, को 300 ° C तक गर्म किये जाते हैं और एक कमरे में छोड़ दिए जाते हैं। इनमें से शीतलन की सबसे धीमी दर किसकी होगी?
(a) Circular plate/ गोलाकार प्लेट
(b) Cube/ घन
(c) Sphere/ गोला
(d) All will cool at the same rate/ सभी एक ही दर पर ठंडे हो जाएँगे

Ans (c)
Sol. In the late of 17th century British scientist Isaac Newton studied cooling of bodies. Experiments showed that the cooling rate is approximately proportional to the difference of temperatures between the heated body and the environment. Surface area or volume ratio is an important influence on temperature control. For same volume sphere has minimum surface area, while circular plate has maximum surface area. So sphere cools slowest and plate cools fastest.

Q3. Optic fibres are used in :
ऑप्टिक फाइबर का उपयोग किया जाता है
(a) CAT scans/ सीएटी स्कैन
(b) X-ray photos/ एक्स-रे फोटो
(c) ultrasound scans/ अल्ट्रासाउंड स्कैन
(d) Endoscopy / एंडोस्कोपी

Ans (d)
Sol. Optical fibres are used in endoscopic instruments that enable doctors to view internal body parts without having to perform surgery. Fernando Alves Martins of Portugal invented the first fiber optic endoscope in 1963-64.

Q4. The snow on the mountains does NOT melt all at once when it is heated by the sun because:
पहाड़ों पर बर्फ, सूरज द्वारा गर्म किये जाने पर है एक साथ नहीं पिघलती क्योंकि-
(a) it becomes very hard/ यह बहुत कठोर हो जाती है
(b) it reflects most of the heat from the sun/ यह सूर्य की अधिकांश ऊष्मा को प्रतिबिंबित करता है
(c) it has a low specific heat capacity/ इसकी निम्न विशिष्ट ताप क्षमता है
(d) it has a high latent heat of fusion/ इसमें संलयन की एक उच्च अव्यक्त ऊष्मा होती है

Ans (b)
Sol. Newly formed snow reflects about 90 per cent of the sunlight that falls upon it. This means that the sun is powerless to melt clean snow. And when snow does melt, it is not because of the sunlight. Snow does not melt on a spring day because of the sun’s heat. It melts because of the warm air from the sea.

Q5. A person standing on a railway platform listens to the whistles of arriving and departing trains. The whistle heard is
रेलवे प्लेटफॉर्म पर खड़ा व्यक्ति आने-जाने वाली ट्रेनों की सीटी सुनता है। सुनाई देने वाली सीटी _____________ है
(a) the same in both cases in all respects/ सभी में दोनों मामलों में समान
(b) of higher intensity when train arrives/ ट्रेन आने पर अधिक तीव्रता की
(c) of higher pitch when train arrives/ ट्रेन आने पर उच्च पिच की
(d) of higher pitch when train departs/ ट्रेन जाने पर उच्च पिच की

Ans (c)
Sol. Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. During propagation, waves can be reflected, refracted, or attenuated by the medium. Now if we consider these cases, then the train which is arriving towards us having whistles of higher pitch because it propagates through a medium which is coming towards us but the train which is leaving propagating trough a medium moving further away from the listener and thus produced whistle of lower pitch.

Q6. The velocity of sound in moist air is more than in dry air because the moist air has
नम हवा में ध्वनि का वेग शुष्क हवा की तुलना में अधिक होता है क्योंकि नम हवा में
(a) less density than dry air/ शुष्क हवा की तुलना में कम घनत्व
(b) less pressure than dry air/शुष्क हवा की तुलना में कम दाब
(c) more pressure than dry air/शुष्क हवा की तुलना में अधिक दाब
(d) more density than dry air/शुष्क हवा की तुलना में अधिक घनत्व

Ans (a)
Sol. The density of dry air is more than that of moist air (when moisture is removed from air, its density increases). The speed of sound in a medium is inversely proportional to the square root of its density. Therefore, the speed of sound in moist air is more than that in dry air.

Q7. The velocity of heat radiation in vacuum is
शून्यक में ऊष्मा विकिरण का वेग ________ होता है
(a) Equal to that speed of light/ प्रकाश की गति के बराबर
(b) Less than that speed  of light/प्रकाश की गति से कम
(c) Greater than that speed of light/ प्रकाश की गति से अधिक
(d) Equal to that speed of sound/ ध्वनि की गति के बराबर
Ans (a)
Sol. It is equal to the speed of light. Thus is because heat, in vacuum travels in the form of ‘Infrared Radiation’, a form of electromagnetic radiation.

Q8. ______ is the perpendicular distance between point of application of force and axis of rotation.
लगाये गये बल के बिंदु और घूर्णन अक्ष के बीच की लंबवत्त दूरी ___ है.
(a) Moment arm/आघूर्ण भुजा
(b) Moment of Inertia/जड़ता प्रवृत्ति
(c) Altitude/शीर्ष-लंब
(d) Base/आधार

Ans.(a)
Sol. Moment Arm is the perpendicular distance between point of application of force and axis of rotation.

Q9. Which among the following is not a unit of distance?
निम्नलिखित में से क्या दूरी की एक इकाई नहीं है?
(a) Light year/लाइट इयर
(b) Longsec/लॉन्गसेक
(c) Astronomical unit/खगोलीय इकाई
(d) Parsec/पार्सेक

Ans.(b)
Sol. Longsec is not the unit of distance.

Q10. The apparent weight of a person in a lift which is moving down with uniform acceleration is _______.
एक लिफ्ट में एक व्यक्ति का स्पष्ट वजन जो एक समान त्वरण के साथ चल रहा है तो _______
(a) greater than the weight when the person is stationary/जब व्यक्ति स्थिर होता है उस वजन से अधिक होता है.
(b) twice the weight when the person is stationary/जब व्यक्ति स्थिर होता है तो वजन का दोगुना होता है.
(c) less than the weight when the person is stationary/जब व्यक्ति स्थिर होता है तो वजन से कम होता है.
(d) same as the weight when the person is stationary/जब व्यक्ति स्थिर होता है तब वज़न के समान होता है

Ans.(c)
Sol. The apparent weight of a person in a lift which is moving down with uniform acceleration is less than the weight when the person is stationary.

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