Q1. (i) List three common refractive defects of vision. Suggest the way of correcting these defects.
(ii) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12-year suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve ‘themselves to create awareness about this fact among people?
Q2. What is atmospheric refraction? Use this phenomenon to explain the following natural events.
(i) Twinkling of stars.
(ii) Advanced sunrise and delayed sunset. Draw diagrams to illustrate your answers.
Q3. What is meant by scattering of light? Mention the factor on which it depends. Explain, why the colour of the clear sky is blue? An astronaut in space finds sky to be dark. Explain reason for this observation.
Q4. (a) Write the function of each of the following parts of human eye: Cornea, iris, crystalline lens, ciliary muscles.
(b) Millions of people of the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organized a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission how would you contribute in this noble cause?
(i) State the objective of organizing such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
Q5. (a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain;
(i) Why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) The type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention.
Q6. A person is unable to see distinctly the printed on a newspaper. Name the defect of vision he is suffering from. Draw ray diagram to Illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
Q7. (i) List three common refractive defects of vision. Suggest the way of correcting these defects.
(ii) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people?
Q8. (i) Name the defect of vision in which the eye loses its power of accommodation due to old age.
(ii) The near point of a person suffering from hypermetropia is at 50 cm from his eye. What is the power of the lens needed to correct this defect/ (near point of normal eye is 25 cm)?
(iii) With the help of ray diagrams, show the formation of image by
(a) a hypermetropic eye.
(b) correction of hypermetropia by using an appropriate lens.
Q9. (a) What is presbyopia? State its cause. How is it corrected?
(b) Why does the Sun appear reddish early in the morning? Explain with the help of a labelled diagram.
Q10. (i) Define dispersion of light. How is scattering of light different from dispersion? Give one example of natural phenomenon based on each of these.
(ii) A beam of light consisting of red, blue and yellow colours is incident on the prisms as shown below. Complete the diagram to show refracted and emergent ray.
Q11. (a) Write an activity for observing scattering of light in colloidal solution.
(b) On the basis of this activity explain, why sky appears red at sunrise or sunset.
Q12. (i) Explain, how do we see different colours of an object?
(ii) Why is it so that some people cannot distinguish between different colours?
(iii) A chick wakes up with the sunrise and sleeps by sunset. How does it manage to do so?
Q13. (i) A doctor has prescribed a corrective lens of -4.2 D to a person suffering from defect of vision.
(a) Identify the defect from which he is suffering.
(b) Is the prescribed lens is diverging or converging? Show the nature of the lens with the help of a ray diagram.
(ii) The person wants to read a book placed at 20 cm, whereas near. point of his eye is 30 cm. Calculate the power of lens required.
Q14. (i) List the parts of the human eye that control the amount of light entering into it. Explain, how they perform this function?
(ii) Write the function of the retina in the human eye.
(iii) Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?