Class 10 Science Chapter 10: The Human Eye and the Colourful World worksheet with answer key
A 20-mark worksheet on The Human Eye and the Colourful World for about 40 minutes of class or homework: 5 multiple-choice, 3 very short answer and 3 short answer questions, written from the NCERT chapter and checked by a second reviewer. Print the PDF for the class; the answer key carries the marking scheme. Teachers may photocopy it freely.
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Answer: (b) outer surface of the cornea
Most refraction occurs at the outer surface of the cornea; the eye lens only provides the finer adjustment of focal length.
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Answer: (a) relax, the lens becomes thinner and its focal length increases
For a distant object the ciliary muscles relax, the lens becomes thin and its focal length increases. Option (b) is the state for a near object; (c) pairs a thicker lens with a longer focal length; (d) pairs contracted muscles with a thinner lens.
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Answer: (c) eyeball has become too small
Hypermetropia arises when the focal length of the eye lens is too long or the eyeball has become too small. Excess curvature and an elongated eyeball cause myopia.
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Answer: (b) iris
The iris is a dark muscular diaphragm that controls the size of the pupil; the ciliary muscles change the curvature of the lens, not the pupil.
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Answer: (c) in front of the retina
In myopia the image of a distant object forms in front of the retina, not on it. Behind the retina is the case of hypermetropia for a near object.
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Air just above the fire is hotter and lighter and has a slightly lower refractive index than the cooler air above it. These conditions keep changing, so light from the object is refracted by varying amounts and its apparent position fluctuates.
- hot air has a lower refractive index than the cooler air above (1)
- the conditions are not steady, so the apparent position keeps changing (1)
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The ciliary muscles modify the curvature of the eye lens and so change its focal length. This ability of the eye lens to adjust its focal length is called accommodation.
- ciliary muscles change the curvature, and so the focal length, of the eye lens (1)
- names accommodation (1)
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(i) The cornea, the thin transparent membrane that forms the bulge on the front of the eyeball. (ii) The aqueous humour.
- cornea (1)
- aqueous humour (1)
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(i) Myopia: the far point comes nearer than infinity. Hypermetropia: the near point moves farther than 25 cm. (ii) Myopia: the image of a distant object forms in front of the retina. Hypermetropia: light from a near object is focussed behind the retina. (iii) Myopia: concave lens. Hypermetropia: convex lens.
- far point nearer than infinity in myopia; near point beyond 25 cm in hypermetropia (1)
- image in front of the retina in myopia; behind the retina in hypermetropia (1)
- concave lens for myopia; convex lens for hypermetropia (1)
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(i) Dispersion of white light. (ii) Violet bends the most, so it is nearest the base; red bends the least, so it is at the top. (iii) Different colours bend through different angles with respect to the incident ray, so they emerge along different paths and become distinct.
- dispersion (1)
- violet nearest the base, red at the top, because violet bends most and red least (1)
- different colours bend through different angles and emerge along different paths (1)
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(i) Very fine particles and air molecules scatter mainly the shorter blue wavelengths, so the clear sky looks blue. Cloud droplets are much larger; when particles are large enough the scattered light appears white. (ii) Scattering of light.
- fine particles and molecules scatter mainly blue (1)
- large particles scatter all colours, so the light appears white (1)
- scattering of light (1)
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