# Physics Questions [LIGHT] for Railway ALP Stage-II Exam : 14th November 2018

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Q1. Light appears to travel in a straight line because-
प्रकाश एक सीधी रेखा में यात्रा करता प्रतीत होता है क्योंकि
(a) It consists of small particles. / इसमें छोटे कण होते हैं
(b) The velocity of light is very large. / प्रकाश का वेग बहुत अधिक है
(c) The wavelength of light is very small. / प्रकाश का तरंगदैर्ध्य बहुत कम है
(d) Light is reflected by the surroundings. / प्रकाश आसपास की वस्तुओं द्वारा प्रतिबिंबित होता है.
Ans.(c)
Sol. Due to its very small wavelength, the light appears to travel in a straight line.

Q2. Human eye is most sensitive to visible light of the wavelength
मानव आंख किस तरंग दैर्ध्य के दृश्यमान प्रकाश के प्रति अधिक संवेदनशील है?
(a) 605nm/ एनएम
(b) 555nm/ एनएम
(c) 450nm / एनएम
(d) 750nm / एनएम

Ans.(b)
Sol. Under daylight conditions, the average normal sighted human eye is most sensitive at a wavelength of 555 nm.

Q3. The speed of light in vacuum is nearly-
वैक्यूम में प्रकाश की गति लगभग कितनी है?
(a) 3 × 10¹⁰ metres/sec
(b) 3×10⁸ metres/sec
(c) 3×10⁸ km/sec
(d) 3×10⁸ light years

Ans.(b)
Sol. The speed of light in a vacuum is 3.00 x 10⁸ m/s, while the speed of sound in vacuum is zero and in air is 343 m/sec. The speed of light in glass is 2,0 × 10⁸ m/s. The velocity of light always greater than the velocity of sound. The velocity of celestial objects and the rockets in quite low than the velocity of light.

Q4 . Which one of the following phenomenon is used in optical fibres?
ऑप्टिकल फाइबर में निम्न में से कौन सी घटना का उपयोग किया जाता है?
(a) Interference / इंटरफेरेंस
(b) Refraction / अपवर्तन
(c) Total internal reflection / कुल आंतरिक प्रतिबिंब
(d) Polarisation / ध्रुवीकरण

Ans.(c)
Sol. The optical fibre is a very thin strand of glass or plastic cable for transmitting light from one point to another. They work on he principle of total internal reflection. There is no loss of signal through an optical fibre.

Q5. Velocity of light is maximum in-
प्रकाश की गति अधिकतम किस में होती है?
(a) Diamond / हीरा
(b) Water /पानी
(c) Vacuum / वैक्यूम
(d) Hydrogen / हाइड्रोजन

Ans.(c)
Sol. The speed of light in vacuum is maximum (c = 3 × 10⁸  ms^(-1)). The speed of light decreases gradually in optically denser mediums like water or glass. It is least in diamond.

Q6. The speed of light will be minimum while passing through-
किससे गुजरते समय प्रकाश की गति न्यूनतम होती है-
(a) Glass / कांच
(b) Vacuum / शून्यक
(c) Water / पानी
(d) Air / हवा

Ans.(a)
Sol. Any of the object or material which has the highest refractive index has the minimum speed of light. The glass has the highest refractive index among other like, vacuum, water and air.

Q7. Waves used for telecommunication are-
दूरसंचार के लिए किस प्रकार की तरंगों का उपयोग किया जाता हैं –
(a) Visible light /दृश्य प्रकाश
(b) Infrared/इन्फ्रारेड
(c) Ultraviolet/पराबैंगनी
(d) Microwave/माइक्रो तंरग
Ans.(d)
Sol. The microwaves are high-frequency signals in the 300 MHz to 300 Ghz range. The signals can carry thousands of channels at the same time, making it a very versatile communication system. Microwave is often used for point-to-point telecommunications. Today microwave is employed by telecommunication industry in the form of both terrestrial relays and satellite communication.
Q8. Light from the Sun reaches Earth in about:
सूर्य से प्रकाश पृथ्वी पर कितनी देर में पहुंचता है:
(a) 2 minutes / मिनट
(b) 4 minutes  / मिनट
(c) 8 minutes / मिनट
(d) 16 minutes / मिनट
Ans.(c)
Sol. The sunlight takes about 500 second or 8.5 minutes to reach to the earth.
Q9. When light waves pass from air to glass the variable affected are-
जब प्रकाश तरंगों को हवा से कांच तक पहुंचा जाता है तो ______ प्रभावित होते हैं-
(a) Wavelength, frequency and velocity/ तरंगदैर्ध्य, आवृत्ति और वेग
(b) Velocity and frequency/वेग और आवृत्ति
(c) Wavelength and frequency/तरंगदैर्ध्य और आवृत्ति
(d) Wavelength and velocity/तरंग दैर्ध्य और वेग
Ans.(d)
Sol. When light passes from air to glass or one medium to another, then the frequency of the light remains constant but wavelength and velocity are changed.

Q10. Which one of the following energy conversion takes place in carrying out the process of photosynthesis?
प्रकाश संश्लेषण की प्रक्रिया को पूरा करने में निम्नलिखित में से कौन सा ऊर्जा रूपांतरण होता है?
(a) Light to chemical energy  / प्रकाश से रासायनिक ऊर्जा
(b) Light to thermal energy / प्रकाश से तापीय ऊर्जा
(c) Thermal to biochemical energy / थर्मल से जैव रासायनिक ऊर्जा
(d) Heat to kinetic energy / ऊष्मा से गतिशील ऊर्जा
Ans.(a)
Sol. Photosynthesis is the process used by plants to convert light energy into chemical energy. Photosynthesis can be represented by using following chemical equation.
6CO₂+6H₂O →(Chlrophyl)-> C₆H₁₂O₆+6O₂
Where CO₂= Carbon dioxide
H₂O=Water
C₆H₁₂O₆=Glucose
O₆=Oxygen

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