NCERT Solutions for Class 10 Physics Chapter 11 : Human Eye and Colorful World

Answer. The earth’s atmosphere is a heterogeneous mixture of minute particles such as smoke, tiny water droplets, suspended particles of dust and molecules of air. When a light beam strikes such minute particles, the path of the beam becomes visible. The light reaches us after it is reflected diffusely by these tiny particles. It is this phenomenon of scattering of light that makes the particles visible and gives rise to the Tyndall effect.

Answer. By donating our eyes after our death, we can give the gift of vision to another person. To be an eye donor you can be of any age or gender. People using spectacles, or operating for cataracts, can also donate their eyes. Also, people with diabetes, hypertension, asthma and without any communicable diseases can donate eyes. However, people who were infected with or died because of AIDS, Hepatitis B or C, rabies, acute leukaemia, tetanus, cholera, meningitis or encephalitis cannot donate their eyes. The eye bank team removes the eyes at the home of the deceased or at a hospital within 4-6 hours after death. The removal process takes only 10-15 minutes. The eye bank evaluates all the donated eyes using strict medical standards. Eyes found unsuitable for transplantation are used for research and medical education. The identities of both the donor and the recipient remain confidential. It is important to note that one pair of eyes gives vision to up to 4 Corneal blind people.

Answer. The three common refractive defects of vision that can be corrected by the use of suitable spherical lenses are: Myopia: In Myopia, a person can see nearby objects clearly but cannot see distant objects distinctly. It is also known as near-sightedness. A person with myopia has the far point nearer than infinity. In myopia, the image of a distant object is formed in front of the retina and not at the retina itself. Hypermetropia: In Hypermetropia, a person can see distant objects clearly but cannot see nearby objects distinctly. This is because the light rays from a close object are focused at a point behind the retina. It is also known as far-sightedness. Presbyopia: In Presbyopia, people find it difficult to see nearby objects comfortably and distinctly without corrective eyeglasses. The reason behind this is that the power of accommodation of the eye usually decreases with ageing. Thus, for many people, the near point gradually recedes away.