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NDA Refraction of Light and Lenses — practice questions — page 2

Explore 34 free Refraction of Light and Lenses questions in NDA Science. Open each question or exercise to read its content, reference answers and available explanation.

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Refraction of Light and Lenses questions and exercises with answers

Showing questions 31–34 of 34.

Twinkling of stars is caused by:Read the answer and worked solution →An old man cannot read a book held close but can see distant scenes clearly. The defect and its cure are:Read the answer and worked solution →Tyndall effect — the visible path of a beam of light through a colloid — is a result of:Read the answer and worked solution →The ability of the eye to focus on objects at different distances is called:Read the answer and worked solution →

Worked practice questions

Twinkling of stars is caused by:

  1. Variation in star brightness
  2. Reflection from clouds at night
  3. Atmospheric refraction in changing air layers
  4. Polarisation by upper atmosphere
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Correct answer: C. Atmospheric refraction in changing air layers

1. Stars are so far away they act as POINT sources. 2. Their light is refracted as it passes through atmospheric layers of varying density. 3. Continuous changes in refraction make the apparent position and brightness fluctuate — twinkling. 4. Planets DON'T twinkle: they are extended sources, fluctuations average out. _Source: syllabus Science Ch 10 §10.4 Atmospheric Refraction_

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An old man cannot read a book held close but can see distant scenes clearly. The defect and its cure are:

  1. Myopia, concave lens corrects
  2. Presbyopia, bifocal needed
  3. Astigmatism, cylindrical lens
  4. Hypermetropia, convex lens corrects
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Correct answer: D. Hypermetropia, convex lens corrects

1. Inability to see NEAR objects = hypermetropia (or its variant in old age, presbyopia). 2. The eye lens has lost flexibility and the near point recedes. 3. CONVEX lens of suitable focal length brings near objects into focus on the retina. 4. If BOTH near and far vision are affected, bifocal lenses are prescribed. _Source: syllabus Science Ch 10 §10.2 Hypermetropia_

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Tyndall effect — the visible path of a beam of light through a colloid — is a result of:

  1. Absorption by the medium
  2. Polarisation by impurities
  3. Refraction by water droplets
  4. Scattering by colloidal particles
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Correct answer: D. Scattering by colloidal particles

1. Colloidal particles (size 1-1000 nm) scatter light strongly. 2. Hence the beam becomes visible from the side — the Tyndall effect. 3. Same effect explains why a beam through a forest mist or smoky room is visible. _Source: syllabus Science Ch 10 §10.5 Scattering (Tyndall effect)_

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