Human Eye and Colourful World

1

In the figure given below, a narrow beam of white light is shown to pass through a triangular glass prism. After passing through the prism, it produces a spectrum XY on the screen.

  1. Name the phenomenon.
  2. State the colours seen at X and Y.
  3. Why do different colours of white light bend at different angles through a prism?
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2

(i) What is visible spectrum?

(ii) Why is red used as the stopping light at traffic signals?

(iii) Two triangular glass prisms are kept together connected through their rectangular side. A light beam is passed through one side of the combination. Will there be any dispersion? Justify your answer.

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3

Why does the sun appear reddish early in the morning? Will this phenomenon be observed by an astronaut on the Moon? Give reason to justify your answer.

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4

Noopur needs a lens of power -4.5D for correction of her vision.

  1. What kind of defect in vision is she suffering from?
  2. What is the focal length and nature of the corrective lens?
  3. Draw ray diagrams showing the (a) defected eye and (b) correction for this defect.
  4. What are the causes of this defect?
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5

Draw a path of light ray passing through a prism. Label angle of incidence and angle of deviation in the ray diagram.

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6

State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms, show that white light is made of seven colours? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination.

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7

What is presbyopia? State its cause. How is it corrected?

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8

Write the function of each of the following parts of human eye:

  1. Cornea
  2. Iris
  3. Crystalline lens
  4. Ciliary muscles
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9

Why do stars twinkle? Explain.

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10

A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.

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