RRB JE Exam: Physics (Light) Quiz | 28th February

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Q1. A ray of light travelling obliquely from denser to rarer medium
प्रकाश की एक किरण सघन से दुर्लभ माध्यम तक यात्रा करती है तो वह
(a) Bends towards the normal/ सामान्य की ओर झुकती है
(b) Bends away from the normal/ सामान्य से दूर झुकती है
(c) Does deviate from its path/ अपने मार्ग से भटक जाती है
(d)None of these/इनमें से कोई नहीं

Show Answer
Ans(b)
Sol. A ray of light travelling obliquely from denser to rarer medium Bends away from the normal.


Q2. The laws of reflection are true for

परावर्तन के नियम किस के लिए सत्य हैं?
(a) The plane mirror only/ केवल समतल दर्पण
(b) The concave mirror only/ केवल अवतल दर्पण
(c) The convex mirror only/ केवल उत्तल दर्पण
(d)All reflecting surfaces/ सभी प्रतिबिंबित सतहों

Show Answer
Ans(d)
Sol. The law of reflection states that the incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane. The laws of reflection are true for all reflecting surfaces.


Q3. The focal length of a plane mirror is

समतल दर्पण की फोकल लंबाई क्या होती है?
(a) Positive/ सकारात्मक
(b) Negative/ ऋणात्मक
(c) Zero /शून्य
(d)Infinity/ अनन्तता

Show Answer
Ans(d)
Sol. The radius of Curvature of plane mirror is infinite, hence the focal length of plane mirror will also be infinite.


Q4. The amount of light reflected depends upon

परिलक्षित प्रकाश की मात्रा किस पर निर्भर करती है?
(a) The nature of material of the object/ वस्तु की सामग्री की प्रकृति पर
(b) The nature of the surface/ सतह की प्रकृति पर
(c) The smoothness of the surface/सतह की चिकनाहट
(d)All the above are correct/ उपरोक्त सभी सही हैं

Show Answer
Ans(d)
Sol. The amount of light reflected depends upon the nature of material of the object ,the nature of the surface and the smoothness of the surface.


Q5. A number of images of a candle flame are seen in thick mirror

मोमबत्ती की लौ की कई छवियां मोटे दर्पण में देखी जाती हैं
(a)The first image is the brightest/ पहली छवि सबसे चमकदार है
(b)The second image is the brightest/ दूसरी छवि सबसे चमकदार है
(c) The last image is the brightest/ अंतिम छवि सबसे चमकदार है
(d)All images are equally brightest/ सभी चित्र समान रूप से उज्ज्वल हैं

Show Answer
Ans(b)
Sol. A number of images of a candle flame are seen in thick mirror the second image is the brightest because of the second image is formed after reflection from rear silvered surface, which sends maximum amount of light.


Q6. Critical angle of light passing from glass to water is minimum for

ग्लास से पानी तक प्रकाश के महत्वपूर्ण कोण _______ के लिए न्यूनतम होता है
(a) Red colour/लाल रंग
(b) Green colour/हरा रंग
(c) Yellow colour/पीला रंग
(d) Violet colour/ बैंगनी रंग

Show Answer
Ans(d)
Sol. Critical angle will be minimum for violet colour of the spectrum. We know that refractive index μ is given as c/v where c is the velocity of light and v is the velocity of the respective colour in the medium. In refraction , the velocity of the red colour is maximum and that of the violet colour is minimum.


Q7. When a ray or light enters a glass slab from air

जब एक किरण या प्रकाश हवा से एक ग्लास स्लैब में प्रवेश करती है, तो-
(a) Its wavelength decreases/ इसका तरंग दैर्ध्य घट जाता है
(b) Its wavelength increases/ इसका तरंग दैर्ध्य बढ़ जाता है
(c) Its frequency increases/ इसकी आवृत्ति बढ़ जाती है
(d) Neighter its wavelength nor its frequency changes/ न तो इसकी तरंग दैर्ध्य और न ही इसकी आवृत्ति में परिवर्तन होता है

Show Answer
Ans(a)
Sol. When a ray or light enters a glass slab from air Its wavelength decreases.


Q8. When light passes from one medium to another, the physical quantity that remains unchanged is

जब प्रकाश एक माध्यम से दूसरे माध्यम से गुजरता है, तो ________ भौतिक मात्रा अपरिवर्तित रहती है
(a) Velocity/ वेग
(b) Wavelength/ तरंग दैर्ध्य
(c) Frequency/ आवृत्ति
(d)None/कोई नहीं

Show Answer
Ans(c)
Sol. The frequency of the light ray remains same when it travels from one medium to another bcoz it depends on the source of light. But the wavelength and speed vary bcoz they depend on the medium through which the light passes.


Q9. A well cut diamond appears bright because

एक तराशा हुआ हीरा चमकदार दिखाई देता है क्योंकि
(a) It emits light/ यह प्रकाश का उत्सर्जन करता है
(b) It is radioactive/ यह रेडियोधर्मी है
(c) Of total reflection/ कुल प्रतिबिंब के कारण
(d) Of dispersion/ फैलाव के कारण

Show Answer
Ans(c)
Sol. A well cut diamond appears bright because of total internal reflection.


Q10. Mirage is observed in a desert due to the phenomenon of

रेगिस्तान में मृगतृष्णा किस घटना के कारण देखी जाती है
(a) Inerference/ इंटरफेरेंस
(b) Total reflection/ कुल प्रतिबिंब
(c) Scattering/ प्रकीर्णन
(d) Double refraction/ डबल अपवर्तन

Show Answer
Ans(b)
Sol. Mirage occurs due to total internal reflection of light (TIR). When the sun is high in the sky, the sand gets heated first and then the layers of air above it. The rays from the trees travel from an optically densper air layer to a rarer layer and hence bend away from the normal.

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