Mock Test

Optics part (1)

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Optics part (1)

Total Questions: 78

41. Which of the following reflects back more sunlight as compared to other three ? [U.P.P.C.S.(pre) 2021]

Correct Answer: (c) land covered with snow
Solution:Land covered with fresh snow reflects back more sunlight as compared to other three. Fresh snow and ice reflect about 80-85% of the sunlight.

The skin of skiers is irradiated by sunlight from all sides, since the snow does not take up the light but reflects it and remains cold. 'Albedo' (Latin meaning-whiteness) is the name given by the scientists to this ability of surfaces to reflect light.

The phenomenon of a body or a surface reflecting a fraction of light is called as ‘Albedo.’ It is used to refer the portion of solar energy reflected from the surface of the Earth back into space. The albedo is particularly high for snow and ice.

42. The technique to integrate and mark the image of a three dimensional object is [R.A.S./R.T.S (PRE) 1996,1999]

Correct Answer: (d) holography
Solution:Holography is a technique of producing a three-dimensional image of an object. Holography can work with sound, light or any wavelength.

Holography is popularly used for preserving the transcripts and for Microfiche (a flat piece of film containing microphotographs of the pages of newspaper, catalogue or other). It is also been used for making three- dimensional feature films.

Audiography:Audiography is related to the recording and study of hearing.

Lexicography: Lexicography is the process of writing, compiling, and editing dictionaries.

Photography:Traditional photography captures two-dimensional images.

43. Which of the following is used to take 3 dimensional pictures - [U.P.P.C.S.(MAINS) 2008, U.P.P.C.S.(pre) 1990]

Correct Answer: (b) holography
Solution:Holography is a technique of producing a three-dimensional image of an object. Holography can work with sound, light or any wavelength.

Holography is popularly used for preserving the transcripts and for Microfiche (a flat piece of film containing microphotographs of the pages of newspaper, catalogue or other). It is also been used for making three- dimensional feature films.

While photography captures images, it does so in two dimensions. Radiography (like X-rays) creates images by using radiation to see inside objects, but it doesn't inherently produce 3D images in the same way holography does.

44. The generating images on a screen by focusing an electronic beam on phosphorus coated screen is called - [R.A.S./R.T.S (PRE) 1994-95]

Correct Answer: (c) raster scan
Solution:Raster scan is used in CRT (cathode ray tube) monitors in which electronics beam is projected by electronic gun to generate an image on the screen.

45. Raman effects deals with the light rays passing through [R.A.S./R.T.S (PRE) 1992]

Correct Answer: (d) all transparent medium
Solution:Raman effect deals with the light rays passing through all transparent medium. according to this a beam of the light traverses a dust free transparent sample of a chemical compound a small fraction of light emerges in direction other than that of the incident beam.

46. For reproducing sound a CD audio player uses a : [I.A.S. (PRE) 2000]

Correct Answer: (c) laser beam
Solution:CD audio players use a ultraviolet laser beam to read the microscopic pits and lands on the surface of the CD. These variations represent the digital audio information, which is then converted into an analog audio signal that we can hear.

Quartz crystal: Quartz crystals are used for their precise oscillations, often in timing circuits, but not directly for reading data from a CD.

Titanium needle: Needles are used in record players (turntables) to physically track grooves on vinyl records. CDs are read optically, not through physical contact with a needle.

Barium titanium ceramic: This material has piezoelectric properties and is used in some transducers, but it's not the primary mechanism for reading data in a CD player.

47. When a CD (compact disc used in audio and video systems) is seen in sunlight, rainbow-like colours seen. This can be explained on the basis of the phenomenon of: [I.A.S. (PRE) 2000]

Correct Answer: (a) Reflection and diffraction
Solution:When a CD is viewed in sunlight rainbow like colours are seen. To understand this phenomenon one has to understand the construction of CD. A CD is a thin, circular disc of metal and plastic. It is actually made of three layers.

Most of a CD is made from a tough, brittle plastic called polycarbonate Sandwiched in the middle there is a thin layer of aluminium Finally, on the top of aluminium, is a protective layer of plastic and lacquer. It acts like a thin film, which is responsible for reflection and diffraction of light.

48. Consider the following statement : [I.A.S. (PRE) 2002]

1.Light of longer wavelength is scattered much more than the light of shorter wavelength.

2.The speed of visible light in water is 0.95 times the speed in vacuum.

3.Radio waves are produced by rapidly oscillating electrical currents.

4.To detect the overspeeding vehicles, police use the Doppler effect of reflected short radio waves

which of these statements are correct ?

Correct Answer: (d) 3 and 4
Solution:According to Rayleigh scattering, the amount of scattering is inversely proportional to the fourth power of the wavelength (Scattering ∝ 1/λ⁴). This means that shorter wavelengths (like blue and violet) are scattered much more strongly than longer wavelengths (like red).

This is why the sky appears blue. Hence, the light of shorter wavelength is scattered much more than the light of longer wavelength. The speed of visible light in water 2.25×108m/sec and the speed of light in vacuum 3.0×108m/sec.

Thus, it is clear that the speed of visible light in water is 0.75 times the speed of light in Vacuum. Radio waves are electromagnetic waves, and they are generated by accelerating electric charges. Police radar guns emit short radio waves towards a vehicle.

The frequency of the reflected waves changes due to the Doppler effect if the vehicle is moving. By measuring the change in frequency (Doppler shift), the speed of the vehicle can be determined. This is a common technique used for speed enforcement. So, the statement 1 and 2 are wrong while statement 3 and 4 are correct. Thus, the correct answer is option (d).

49. Assertion (A): In a motion picture, usually 24 frames are projected every second over the whole length of the film. [I.A.S. (PRE) 2000]

Reason (R): An image formed on the retina of eye persists for about 0.1s after the removal of the stimulus.

Correct Answer: (c) (A) is true but (R) is false
Solution:Statement (A) is correct but the reason (R) is false because the image formed on the retina of the persists for about 1/16 of a second after the removal of stimulus.

50. Television signals cannot be received beyond a certain distance because : [U.P.P.S.C. (GIC) 2010 U.P.P.C.S. (Pre) 1994]

Correct Answer: (d) The surface of the Earth is curved
Solution:Earth's Curvature: Due to the Earth's curved surface, there will be a point where the horizon obstructs the direct path between the transmitting antenna and the receiving antenna. Beyond this point, the signal cannot travel directly.

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