12th Class Physics Ray Optics Question Bank

done Case Based (MCQs) - Ray Optics and Optical Instruments Total Questions - 25

• question_answer1)

  Directions (Q. No. 1 to 5):

  Read the following text and answer the following questions on the basis of the same:

  Sparking Brilliance of Diamond:

  The total internal reflection of the light is used in polishing diamonds to create a sparking brilliance.

  By polishing the diamond with specific cuts, it is adjusted the most of the light rays approaching the surface are incident with an angle of incidence more than critical angle. Hence, they suffer multiple reflections and ultimately come out of diamond from the top. This gives the diamond a sparking brilliance.

  Light cannot easily escape a diamond without multiple internal reflections. This is because:
  A)
  its critical angle with reference to air is too large. done clear
  B)
  its critical angle with reference to air is too small. done clear
  C)
  the diamond is transparent. done clear
  D)
  rays always enter at angle greater than critical angle. done clear
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• question_answer2)
  The critical angle for a diamond is \[{{24.4}^{o}}\]. Then its refractive index is:
  A)
  2.42 done clear
  B)
  0.413 done clear
  C)
  1 done clear
  D)
  1.413 done clear
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• question_answer3)
  The basic reason for the extraordinary sparkle of suitably cut diamond is that:
  A)
  it has low refractive index. done clear
  B)
  it has high transparency. done clear
  C)
  it has high refractive index. done clear
  D)
  it is very hard. done clear
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• question_answer4)
  A diamond is immersed in a liquid with a refractive index greater than water. Then the critical angle for total internal reflection will:
  A)
  depend on the nature of the liquid. done clear
  B)
  decrease. done clear
  C)
  remains the same. done clear
  D)
  increase. done clear
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• question_answer5)

  The following diagram shows same diamond cut in two different shapes.

  The brilliance of diamond in the second diamond will be:

  A)
  less than the first. done clear
  B)
  greater than first. done clear
  C)
  same as first. done clear
  D)
  will depend on the intensity of light. done clear
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• question_answer6)

  Directions (Q. No. 6 to 10):

  Read the following text and answer the following questions on the basis of the same:

  Photometry:

  The measurement of light as perceived by human eye is called photometry. Photometry is measurement of a physiological phenomenon, being the stimulus of light as received by the human eye, transmitted by the optic nerves and analysed by the brain. The main physical quantities in photometry are (i) the luminous intensity of the source, (ii) the luminous flux or flow of light from the source and (iii) illuminance of the surface. The SI unit of luminous intensity (I) is candela (cd).

  The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency \[540\text{ }\times \text{ }{{10}^{12}}\] Hz and that has a radiant intensity in that direction of 1/683 watt per steradian, If a light source emits one candela of luminous intensity into a solid angle of one steradian, the total luminous flux emitted into that solid angle is one lumen (1m). A standard 100 watt incandescent light bulb emits approximately 1700 lumens.

  What is photometry?
  A)
  Measurement of light as perceived by human eye done clear
  B)
  Measurement of number of photons emerging from a light source done clear
  C)
  Measurement of electrons emitted by photosensitive surface done clear
  D)
  Measurement of photosensitivity   done clear
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• question_answer7)
  Light received by human eye is analysed by:
  A)
  retina done clear
  B)
  brain done clear
  C)
  optic nerve done clear
  D)
  nervous system done clear
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• question_answer8)
  The SI unit of luminous intensity is:
  A)
  Dioptre done clear
  B)
  Steradian done clear
  C)
  Candela done clear
  D)
  Lumen done clear
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• question_answer9)
  Unit of luminous flux is:
  A)
  Candela done clear
  B)
  Steradian done clear
  C)
  Nit done clear
  D)
  Lumen done clear
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• question_answer10)
  A standard 100 watt incandescent light bulb emits approximately:
  A)
  1700 Lumen done clear
  B)
  700 Lumen done clear
  C)
  1200 Lumen done clear
  D)
  1000 Lumen done clear
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• question_answer11)

  Directions (Q. No. 11 to 15):

  Read the following text and answer the following questions on the basis of the same:

  Optical Fibre:

  Optical fibre works on the principle of total internal reflection. Light rays can be used to transmit a huge amount of data, but there is a problem here - the light rays travel in straight lines. So unless we have a long straight wire without any bends at all, harnessing this advantage will be very tedious.

  Instead, the optical cables are designed such that they bend all the light rays' inwards (using TIR).

  Light rays travel continuously, bouncing off the optical fibre walls and transmitting end to end data. It is usually made of plastic or glass.

  Modes of transmission: Single-mode fibre is used for long-distance transmission, while multi- mode fiber is used for shorter distances. The outer cladding of these fibres needs better protection than metal wires. Although light signals do degrade over progressing distances due to absorption and scattering. Then, optical Regenerator system is necessary to boost the signal.

  Types of Optical Fibres: The types of optical fibers depend on the refractive index, materials used, and mode of propagation of light. The classification based on the refractive index is as follows:

  • Step Index Fibres: It consists of a core surrounded by the cladding, which has a single uniform index of refraction.

  •  Graded Index Fibres: The refractive index of the optical fibre decreases as the radial distance from the fibre axis increases.

  Optical fibre works on the principle of:
  A)
  scattering of light. done clear
  B)
  diffraction of light. done clear
  C)
  total internal reflection of light. done clear
  D)
  dispersion of light.   done clear
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• question_answer12)
  For long-distance transmission:
  A)
  single mode fibre is used. done clear
  B)
  multi-mode fibre is used. done clear
  C)
  both single mode and multi-mode are used. done clear
  D)
  any one of single mode or multi-mode may be used. done clear
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• question_answer13)
  Optical fibre is made of:
  A)
  copper done clear
  B)
  semiconductor done clear
  C)
  plastic or glass done clear
  D)
  superconductors done clear
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• question_answer14)
  In graded index optical fibre:
  A)
  the refractive index of the optical fibre increases as the radial distance from the fibre axis increases. done clear
  B)
  the refractive index of the optical fibre decreases as the radial distance from the fibre axis increases. done clear
  C)
  the refractive index of the optical fibre remains same throughout. done clear
  D)
  inner side of cladding is mirrored to ensure reflection. done clear
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• question_answer15)
  Light signal through optical fibre may degrade due to:
  A)
  refraction. done clear
  B)
  refraction and reflection. done clear
  C)
  diffraction and scattering. done clear
  D)
  scattering and absorption. done clear
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• question_answer16)

  Directions (Q. No. 16 to 20):

  Read the following text and answer the following questions on the basis of the same:

  Negative Refractive Index:

  One of the most fundamental phenomena in optics is refraction. When a beam of light crosses the interface between two different materials, its path is altered depending on the difference in the refractive indices of the materials. The greater the difference, the greater the refraction of the beam.

  For all known naturally occurring materials the refractive index assumes only positive values. But does this have to be the case?

  In 1967, Soviet physicist Victor Veselago hypothesized that a material with a negative refractive index could exist without violating any of the laws of physics.

  Veselago predicted that this remarkable material would exhibit a wide variety of new optical phenomena. However, until recently no one had found such a material and Veselago's ideas had remained untested. Recently, meta-material samples are being tested for negative refractive index. But the experiments show significant losses and this could be an intrinsic property of negative- index materials.

  Snell's law is satisfied for the materials having a negative refractive index, but the direction of the refracted light ray is 'mirror-imaged' about the normal to the surface.

  There will be an interesting difference in image formation if a vessel is filled with "negative water" having refractive index - 1.33 instead of regular having refractive index 1.33.

  Say, there is a fish in a vessel filled with negative water. The position of the fish is such that the observer cannot see it due to normal refraction since the refracted ray does not reach to his eye.

  But due to negative refraction, he will be able to see it since the refracted ray now reaches his eye.

  Who hypothesized that a material may have negative refractive index ?                         
  A)
  Joseph Von Fraunhofer   done clear
  B)
  Augustin-Jean Fresnel     done clear
  C)
  Thomas Moore done clear
  D)
  Victor Veselago done clear
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• question_answer17)
  Is Snell's law applicable for negative refraction?
  A)
  Yes done clear
  B)
  No done clear
  C)
  Unpredictable done clear
  D)
  Yes, only for normal incidence done clear
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• question_answer18)
  A ray in incident on normal glass and "negative glass" at an angle \[{{60}^{o}}\]. If the magnitude of angle of refraction in normal glass is \[{{45}^{o}}\] then, what will be the magnitude of angle of refraction in the "negative glass"?                                
  A)
  Less than \[{{45}^{o}}\] done clear
  B)
  More than \[{{45}^{o}}\] done clear
  C)
  \[{{45}^{o}}\] done clear
  D)
  Unpredictable        done clear
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• question_answer19)
  When the angle of incidence will be equal to angle of refraction for material having negative refraction index?                                        
  A)
  When angle of incidence = \[{{90}^{o}}\] done clear
  B)
  When angle of incidence = \[{{0}^{o}}\] done clear
  C)
  It will vary from material to material done clear
  D)
  It is never possible done clear
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• question_answer20)
  Which of the following is the intrinsic property of negative-index materials?
  A)
  Significant gain of light energy due to refraction done clear
  B)
  No loss of light energy due to refraction done clear
  C)
  Significant loss of light energy due to refraction done clear
  D)
  Loss of energy due to refraction in intermittent done clear
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• question_answer21)

  Directions (Q. No. 21 to 25):

  Read the following text and answer the following questions on the basis of the same:

  First Surface Mirror:

  Normally we use back surface mirrors. These are considered low precision mirrors because they actually have two reflecting surfaces. The first reflecting surface is the initial surfaces on the pane of glass where a small percentage of light is reflected off the surface. The second reflecting surface is the aluminium coating where a high percentage of light is reflected off the surface.

  This dual reflection effect of a low precision mirror causes a loss of contrast and image distortion that is undesirable in high precision applications like rear projection systems, scanners and reflecting telescopes. In these cases good image quality is highly preferred, and this is where a front surface mirror is desired for clarity and single image reflection. First surface mirrors are quite common in professional optics. However, compared with back surface mirrors, they have the important disadvantage of being substantially more sensitive.

  The front surface may be touched, and a metal coating on the front surface is substantially more sensitive than a bare glass surface. For example, fingerprints can easily cause oxidation of the metal.. Also, moisture or may cause oxidation of the mirror coating.

  Precision of back surface mirrors is:
  A)
  high. done clear
  B)
  low. done clear
  C)
  depends on intensity of light. done clear
  D)
  similar to first surface mirror. done clear
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• question_answer22)
  Light incident on back surface mirror suffers:
  A)
  two reflections. done clear
  B)
  one reflection. done clear
  C)
  two reflections and two refractions. done clear
  D)
  one refraction and one reflection. done clear
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• question_answer23)
  In professional optics:
  A)
  first surface mirrors are used. done clear
  B)
  back surface mirrors are used: done clear
  C)
  both type of mirrors are used. done clear
  D)
  mirrors are not used. done clear
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• question_answer24)
  Image formed of front coated mirror:
  A)
  suffers astigmatism done clear
  B)
  is brilliant done clear
  C)
  has low contrast done clear
  D)
  is a dual image done clear
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• question_answer25)
  The front surface coating:
  A)
  is susceptible to moisture. done clear
  B)
  is not so sensitive. done clear
  C)
  is worse than back surface coating. done clear
  D)
  cannot prevent dual reflection.   done clear
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