Here you get the CBSE Class 10 Science chapter 11, Human Eye and Colourful World: NCERT Exemplar Problems and Solutions (Part-II). This part of the chapter includes solutions for Question No. 15 to 24 from the NCERT Exemplar Problems for Class 10 Science Chapter: Human Eye and Colourful World. These questions include only the Short Answer Type Questions framed from various important topics in the chapter. Each question is provided with a detailed explanation.
NCERT Exemplar problems are a very good resource for preparing the critical questions like Higher Order Thinking Skill (HOTS) questions. All these questions are very important to prepare for CBSE Class 10 Science Board Examination 2017-2018 as well as other competitive exams.
Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Human Eye and Colourful World:
Short Answer Type Questions
Question 15. Draw ray diagrams each showing
(i) myopic eye and
(ii) hypermetropic eye.
(i) Myopic eye: myopia is caused by elongation of eyeball which results in focusing of image in front of retina. Thus, the distant images are blurry but the nearby images are clear.
(ii) Hypermetropic eye : Loss of flexibility is characterized by focusing of image behind the retina. In this case, distant images are clear but the nearby images are blurry and the condition is termed as hypermetropia.
Question 16. A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor given to her? Draw ray diagram for the correction of this defect.
Student is having myopia which is caused by elongation of eyeball resulting in focusing of image in front of retina. Thus, the distant images are blurry but the nearby images are clear.
Wearing of concave lens diverge the light rays to help the image to be focused on the retina; myopia is corrected using the concave lens.
Question 17. How are we able to see nearby and also the distant objects clearly?
Eyes have ability to adjust its focal length which is known as power of accommodation and we can see nearby and also the distant objects clearly. Relaxation of muscles makes the lens thinner and its focal length increases to make us see the distant objects clearly. Contraction of ciliary muscles increases the curvature of the eye lens and makes the eye lens thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.
Question 18. A person needs a lens of power ─4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
(c) What is the nature of the corrective lens?
(a) The negative power of lens suggests that she must be suffering from myopia.
(b) Power, P = ─4.5 D, focal length, f = ?
Now, P = 1/ f
⟹ f = 1/ P = 1/ −4.5 = −0.222m = − 22.2 cm
(c) Myopia is corrected using concave or divergent lens.
Question 19. How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.
When the second identical prism placed in an inverted position with respect to the first prism, the condition is fulfilled.
Question 20. Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also indicate the order of the colours of the spectrum obtained.
Question 21. Is the position of a star as seen by us its true position? Justify your answer.
No, light of stars enters the earth’s atmosphere and undergoes refraction continuously before reaching the earth. The atmospheric refraction takes place in under gradually changing refractive index. Since, star light is bent towards the normal; star appears slightly higher than the actual position.
Question 22. Why do we see a rainbow in the sky only after rainfall?
Raindrops present in atmosphere after rainfall serve as prism and refract, disperse and internally reflect the incident sunlight followed by final refraction. The whole sequence of dispersion and internal reflection leads to formation of rainbow after rainfall in sky.
Question 23. Why is the colour of the clear sky blue?
It is caused by Rayleigh scattering of sunlight. The molecules in the air scatter blue light more than red light as blue light has shortest wavelength as compared to that of red light which has about 1.8 times greater than blue light.
Question 24 What is the difference in colours of the sun observed during sunrise/sunset and noon? Give explanation for each.
During sunrise/sunset, the sun looks reddish because at this stage, Sun rays travel longer distance in atmosphere and the red light having largest wavelength is scattered the least. Sun is directly over head and sunlight travel relatively shorter distance causing only little of the blue and violet colors to be scattered.
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