CBSE Important Questions Class 10 Science Chapter 10 – The Human Eye and the Colourful World
Class 10 Science Chapter 10 The Human Eye and the Colourful World is part of the CBSE Class 10 Science syllabus. It explains the structure and working of the human eye, the power of accommodation, defects of vision such as myopia, hypermetropia and presbyopia and how lenses correct them. It also covers the refraction of light through a prism, dispersion of white light, the formation of a rainbow, atmospheric refraction and the scattering of light.
These CBSE important questions for Class 10 Science Chapter 10 cover the structure and working of the eye, the power of accommodation and the near and far points, myopia and hypermetropia with their corrections, why the sky looks blue and the Sun looks red at sunset, and numerical problems on concave mirrors. Every question has a clear step-by-step answer in simple English with figures, so students can practise on their own, parents can check the working, and teachers can use them for class tests.
Important Questions Class 10 Science Chapter 10
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Q1. The human eye is one of the most valuable and sensitive organs that
(a) enables us to see the wonderful world and colours around us
(b) can identify objects
(c) is like a camera
(d) all of these
Answer: (d) all of these
The eye lets us see the world and its colours, lets us recognise objects, and works very much like a camera: the lens forms an image on the retina just as a camera lens forms an image on the film or sensor. All three statements are therefore correct.
Q2. Which of the following can be excluded from the description of the working of the human eye?
(a) The lens system forms an image on a light-sensitive screen called the retina.
(b) Light enters the eye through a thin membrane called the cornea.
(c) Rainbow is formed due to splitting of white light.
(d) Iris is a dark muscular diaphragm that controls the size of the pupil.
Answer: (c) Rainbow is formed due to splitting of white light.
Options (a), (b) and (d) all describe parts of the eye and how it works. A rainbow is formed in the sky when sunlight is refracted and dispersed by water droplets. It has nothing to do with the working of the eye, so this statement can be excluded.
Q3. Explain the working of the human eye.
Answer: Light from an object first falls on the cornea, the transparent front layer, which bends most of the light.
The light then passes through the pupil, the hole in the centre of the iris. The iris makes the pupil smaller in bright light and larger in dim light, so that the right amount of light enters.
The light next passes through the eye lens, which is convex. The lens brings the rays together and forms a real and inverted image on the retina.
The light-sensitive cells of the retina change this image into electrical signals, which the optic nerve carries to the brain. The brain reads these signals and we see the object the right way up.
Q4. Explain the structure of the human eye.
Answer: The human eyeball is almost round, about 2.3 cm across. Its main parts are:
• Sclera: the tough white outer coat that protects the inner parts.
• Cornea: the thin, transparent front layer. Most of the bending of light happens here.
• Iris: the coloured part, which may be brown, black, blue or green. It controls how much light enters.
• Pupil: the opening at the centre of the iris, through which light passes.
• Eye lens: a convex lens held by the ciliary muscles. It focuses light on the retina.
• Ciliary muscles: they change the thickness of the lens, and so its focal length, according to how far the object is.
• Retina: the screen at the back of the eye where a real, inverted image is formed.
• Optic nerve: carries the signals from the retina to the brain.
Q5. What is the power of accommodation of the eye? What is the near point and the far point of a normal eye?
Answer: The ability of the eye lens to change its focal length so that we can see both near and distant objects clearly is called the power of accommodation. The ciliary muscles do this work: they relax to make the lens thin for distant objects and contract to make it thick for nearby objects.
The near point is the closest point at which the eye can see an object clearly without strain. For a normal young adult it is about 25 cm.
The far point is the farthest point the eye can see clearly. For a normal eye it is at infinity.
Q6. An object is placed at a distance of 15 cm in front of a concave mirror and forms an image of magnification 3.5. Find the focal length of the concave mirror.
Answer: Given u = −15 cm and the image is magnified 3.5 times. For a real, inverted image, m = −3.5.
m = −v/u, so −3.5 = −v/(−15), which gives v = −52.5 cm.
Using the mirror formula 1/f = 1/v + 1/u:
1/f = 1/(−52.5) + 1/(−15) = −0.01905 − 0.06667 = −0.08571
f = −11.67 cm (about −11.7 cm)
The negative sign confirms it is a concave mirror.
Q7. An object of height 5 cm is placed at a distance of 20 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror will the image be formed? What is the nature and size of the image?
Answer: Given u = −20 cm, f = −15 cm, h = 5 cm.
Using 1/v + 1/u = 1/f:
1/v = 1/f − 1/u = 1/(−15) − 1/(−20) = −4/60 + 3/60 = −1/60
v = −60 cm, so the image is 60 cm in front of the mirror.
m = −v/u = −(−60)/(−20) = −3
Height of image = m × h = −3 × 5 = −15 cm.
So the image is real, inverted, 15 cm tall and three times larger than the object.
Q8. An object placed at the focus, F, of a concave mirror will produce an image
(a) at focus
(b) at infinity
(c) at the centre of curvature
(d) beyond the centre of curvature
Answer: (b) at infinity
Rays coming from the focus become parallel to the principal axis after reflection. Parallel rays never meet at any finite distance, so the image is said to be formed at infinity. It is highly enlarged, real and inverted.
Q9. An object is placed at a distance of 50 cm from the pole of a concave mirror. The mirror forms a real, inverted image of the object on the same side at 62.5 cm from the pole. The focal length of the mirror is
(a) −0.036 cm
(b) +0.036 cm
(c) −27.78 cm
(d) +27.78 cm
Answer: (c) −27.78 cm
Here u = −50 cm and v = −62.5 cm (real image in front of the mirror).
1/f = 1/v + 1/u = 1/(−62.5) + 1/(−50) = −0.016 − 0.020 = −0.036
f = 1/(−0.036) = −27.78 cm
Q10. What is myopia and hypermetropia? How can each defect be corrected?
Answer: Myopia (short-sightedness): the person can see nearby objects clearly but not distant ones. The image of a distant object falls in front of the retina. This happens because the eyeball is too long or the lens is too curved. It is corrected by using a concave lens of suitable power, which spreads the rays slightly so the image falls on the retina.
Hypermetropia (long-sightedness): the person can see distant objects clearly but not nearby ones. The image of a near object falls behind the retina, because the eyeball is too short or the lens is too flat. It is corrected by using a convex lens, which brings the rays together earlier so the image falls on the retina.
Q11. An object placed at the centre of curvature, C, of a concave mirror will produce an image
(a) at infinity
(b) at the centre of curvature, C
(c) at focus, F
(d) beyond the centre of curvature, C
Answer: (b) at the centre of curvature, C
When the object is at C, that is u = R, the mirror formula gives v = R as well. So the image is formed at C itself. It is real, inverted and exactly the same size as the object.
Q12. Why does the sky appear blue, and why does the Sun appear reddish at sunrise and sunset?
Answer: Blue sky: Sunlight is made of many colours. When it passes through the air, the tiny molecules of the atmosphere scatter the light. Blue light has a shorter wavelength than red, and shorter wavelengths are scattered much more strongly. This scattered blue light comes to our eyes from all parts of the sky, so the sky looks blue. This is called the scattering of light.
Reddish Sun at sunrise and sunset: At these times the Sun is near the horizon, so its light has to travel through a much thicker layer of air to reach us. Most of the blue light is scattered away on the long path, and mainly the red and orange light reaches our eyes. That is why the Sun looks reddish in the morning and evening but white at noon.
Related Study Material on Extramarks
- CBSE Important Questions Class 10 Science Chapter 1
- CBSE Important Questions Class 10 Science Chapter 2
- CBSE Important Questions Class 10 Science Chapter 3
- CBSE Important Questions Class 10 Science Chapter 4
- CBSE Important Questions Class 10 Science Chapter 5
- CBSE Important Questions Class 10 Science Chapter 6
- CBSE Important Questions Class 10 Science Chapter 7
- CBSE Important Questions Class 10 Science Chapter 8
- CBSE Important Questions Class 10 Science Chapter 9
- CBSE Important Questions Class 10 Science Chapter 11
- CBSE Important Questions Class 10 Science Chapter 12
- CBSE Important Questions Class 10 Science Chapter 13
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