Question and Answers on the Topic Human Eye

Question and answers on the topic human eye, dispersion, scattering, and common eye defects. Tips to score well Practice diagrams: Learn all ray diagrams and how to label them. correctly. Understand concepts; → revise regularly: Go through the following key points daily. → Human eye, Near point, Far point, Power of accommodation → Eye defects: Reasons and Remedies →Dispersion of light → Formation of rainbow → Persistence of vision → Scattering of light → Wavelength and scattering → Colours of the rising and setting sun → Tyndal effect Solve previous years' questions: This will help you to understand the exam pattern. With proper preparation and practice, you can easily score high marks. 1. When light passes through a medium, it suffers partial and irregular reflection as it hits the particles of the medium. Name this phenomenon. Ans: Scattering of light 2. Newton's colour disc appears white when it is rotated at high speed. Explain. Answer: It is due to the persistence of vision. When we see an object, its image remains on the retina of our eye for 1/16 second after seeing it. This phenomenon is called persistence of vision. When Newton's disc is rotated rapidly, each colour reaches the retina one by one within this 1/16th second period. As a result, the observer experiences the merging of seven colours. This gives the appearance of white colour. 3. What is the distance to the near point from an eye with healthy vision? Ans: 25 cm 4. In which condition do all the component colours of white light undergo the same scattering? Answer: When the size of the particles is larger than the wavelength of light. 5. White light splits into its constituent colours when passed through a glass prism. (a) Name the process of splitting. (b) Give reasons for this splitting. (c) Draw the diagram for recombining the colours produced by the prism. Ans: a. Dispersion. b. Dispersion depends on the wavelength of light. The constituent colours of light have different wavelengths. So, they undergo deviation at different angles and get separated. c. 6. The figure shows image formation in the eye. Observe the figure and answer the following. (a) Where is the image formed? (In front: of the retina, at the retina, behind the retina) (b) Identify the defect of the eye shown in the figure. (c) What are the reasons for this defect?: (d) How can we rectify this defect? Ans: a. Behind the retina b. Hypermetropia (Long-sightedness) c. (i) The focal length of the eye lens is longer than the required length. (ii) Eyeball is smaller than normal size. d. By using a convex lens of suitable power. 7. A doctor's prescription for a person with defective vision has the figures -1.25D, -1.75D. (a) What do these figures indicate? Which type of lens is used here? (b) Identify the defect of the eye. (c) Write the reason for this defect. Ans: a. They indicate the power of the lens. Concave lens. b. Myopia (Short-sightedness) c. (i) The focal length of the eye lens is shorter than the required length. (ii) Eyeball is larger than the normal size. 8. Which of the given statements is true? (a) Long-sightedness can be rectified by using a concave lens of suitable power. (b) Near point of a person with long- sightedness is more than 25 cm. (c) Far point of a person with near- sightedness is at infinity. (d) Short-sightedness can be rectified by using a convex lens of suitable power. Ans: b. Near point of a person with long- sightedness is more than 25 cm. 9. Figure shows the dispersion of a ray of light passing through a water drop in the atmosphere. (a) What are the phenomena of light that the ray undergoes inside the drop? (b) What is dispersion? (c) Identify and write down the colours P and Q. (d) What are the colours seen in the inner and outer edges of a primary rainbow? Ans: a. Refractions, dispersion and internal reflection. b. Dispersion is the splitting up of a composite light into its constituent colours. c. P: Violet, Q: Red d. Inner edge: Violet, Outer edge: Red 10. Describe an experiment to show the scattering of light according to the scheme given below. (a) List the materials to be used. (b) Write the procedure of the experiment. Answer: a. Sodium thiosulphate, Hydrochloric acid, torch, a rectangular glass beaker, water, and a screen. b. Take some sodium thiosulphate solution in a beaker and add a few drops of hydrochloric acid. Then the torch light is passed through the solution. And the emerging light is focused on the screen. A gradual colour change can be seen on the screen. Here, the light from the torch undergoes scattering due to the colloidal sulphur particles present in the solution