NCERT Solutions for Class 10 Science Chapter 11 Human Eye Class 10 are made by our team of subject experts at Toppr. NCERT Solutions for Class 10 Science Chapter 11- Human Eye and Colorful World are curated strictly in accordance with the CBSE Curriculum and the exam pattern. The NCERT textbook questions are answered in a way to provide you with a better understanding of the concepts. Also, the MCQs and long and short questions are all answered according to the weightage and the exam pattern. As Class 10 exams are Board exams, NCERT Solutions provided by Toppr are the best study material to excel in the exams. These solutions will not only help the students in preparing for the board exams but also for the Olympiads. With the help of NCERT Solutions for Science Chapter 11- Human Eye and Colorful World Class 10 you can also analyze your shortcomings and work on them before the exams. These are the best resources designed after proper research and study to assist the students in scoring good marks.
Hint:- In order to view the distances beyond , the focal length of the lens should be .
Step 1:- Note the Given values
The person can't see objects beyond directly
So, in order to view the distances beyond , the focal length of the lens should be .
Step 2:- Calculate power of lens
Now, the power
So, the person suffers from Myopia, the corrective lens will be concave or diverging lens.
Hence, the power is
The person is suffering from myopia and hence need a concave lens to correct the defect. The lens should be such that an object at infinity must form its image at the far point.
The power of the lens can be obtained as:
Hypermetropia can be corrected by using a convex lens. A convex lens converges the incoming light such that the image is formed on the retina.
An object at 25 cm forms an image at the near point of the hypermetropic eye. Here, near point is 1 m.
From lens formula,
Ciliary muscles contract and expand to change the focal length of eye lens so that it is able to see objects at variable distances. However, too much contraction lays a lot of stress on the eye muscles and when objects are closer than the near point(25 cm), the eye is unable to focus its image on retina. Hence, a normal eye cannot see objects closer than 25 cm clearly.
Image in human eyes always formed on retina which doesn’t depend how far the object is from eye. If object is too far, in that case lens will become more thinner and it results into increase in focal length of eye and due to which image will be captured on retina.
On increasing the distance of an object from eye, image distance will remain unchanged.
Question 1. Explain the Tyndall Effect.
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.
Question 2. Write a short note on the donation of eyes.
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.
Question 3. What are the common refractive defects of vision?
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.