HUMAN EYE AND THE COLOURFUL WORLD– 3 Mark Question

Q1. Draw a labelled diagram of human eye. What is the significance of the blind spot?

Q2. List two main causes of a person developing nearsightedness. Show with the help of a ray diagram how this defect can be corrected.

Q3. Study the diagram given below and answer the questions that follows:

Human Eye_01

(i) Which defect of vision is represented in this case? Give reason for your answer.

(ii) What could be the two causes of this defect?

(iii) With the help of a diagram show how this defect can be corrected by the use of a suitable lens?

Q4. Sun is visible 2 min before actual sunrise and 2 min after sunset. Give reason.

Q5.         (i)  Why does the power to see near objects as well as far off objects clearly diminish

               (ii) The far point of a myopic eye is 60 cm. Find the focal length of the lens used to correct it.                 

Q6. With the help of ciliary muscles, the human eye can change its curvature and thus alter the focal length of its lens. State the changes that occur in the curvature and focal length of the eye lens while viewing:

(a) a distant object,

(b) nearby objects.

Explain, why a normal eye is not able to see distinctly the object placed closer than 25 cm, without putting any strain on the eye.

Q7. Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision.  Explain the structure and function of such a lens.

Q8. (i) Make a ray diagram to show how the eye defect myopia is corrected by using a suitable lens.

         (ii) State two reasons due to which this eye defect may be caused.

         (iii) A person with   myopic eye cannot see objects beyond a distance of 1.5 m. What is the power of the lens required to correct the problem?

Q9. Explain why?

(i) Myopic person prefers to remove his spectacles while reading a book.

(ii) A hypermetropic person prefers to remove the spectacles while looking at the sky?

Q10. A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Find the nature, focal length and power of the lens he requires for his spectacles.

Q11. What is meant by scattering of light? The sky appears blue and the sun appears reddish at sunrise and sunset. Explain these phenomena with reason.

Q12. How does refraction of light take place in the atmosphere? Explain the reason why stars appear to twinkle and the planets do not twinkle.

Q13.  Define angle of deviation. Why do different components of white light split up into spectrum when it passes through a triangular glass prism?  Show the angle of deviation for red colour when white light passes through a prism.

Q14. Name the phenomenon associated with the following:

(i) The sky appears blue.

(ii) Formation of a rainbow in the sky.

(iii) Twinkling of stars.

Q15. Explain in brief the reason for each of the following:

(i) The sun appears reddish during sun-rise.

(ii) At noon the sun appears white.

(iii) To an astronaut the sky appears dark instead of blue.

Q16. Describe an activity to show that the colours of white light split by a glass prism can be recombined to get white light  by another  identical  glass prism. Also, draw ray diagram to show the recombination of the spectrum of white light.

Q17. What is Tyndall effect? What is its causes? Name two phenomena observed in daily life which are based on Tyndall effect.

Q18.  Draw a labelled diagram of human eye. What is the significance of the blind spot and the yellow spot?

Q19.  Describe the formation of rainbow in the sky with the help of suitable diagram.

Q20.  List three common refractive defects of vision and suggest the way of correcting these defects.

Q21.   State the role of ciliary muscles in accommodation.

Q22.   Why we have two eyes to view the objects?

Q23.   What is the result of dispersion of white light?

Q24.   What is the difference in colours of the Sun observed during sunrise/sunset and noon?  Give explanation for each.

Q25.   How does the thickness of the eye lens change when we shift looking from a distant tree to reading a book?

Q26.  A person got his eyes tested. The optician prescription for the spectacles read.

Left eye= -3 D and right eye= -3.5 D

Discuss the defects of which a person is suffering.

Q27.  The power of a lens is +1.5 D. Name the type of defects of vision that can be corrected by using this lens. Find the focal length of the lens.

Q28. A person is able to see objects clearly only when these are lying at distance between  50 cm and 300 cm from his eyes. Name the kind of defects of vision he is suffering from.

Q29. What will be the angle of deviation through a prism angle 60 °, when angles of incidence and emergence are 45° each?

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