Class 10 Science · Chapter 10

The Human Eye and the Colourful World

163 Class 10 Science questions on The Human Eye and the Colourful World from the NCERT textbook, NCERT Exemplar and CBSE board papers 2023–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 4 of 9

1. Q61 CBSE 2026
   Name the ​phenomenon due to which a prism splits the incident ​white light into ​a ​band ​of ​colours. State the reason ​of the ​phenomenon also.
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   Dispersion: white light is a mixture of seven colours, and glass has a different refractive index for each, so they bend differently.

   The phenomenon is dispersion of white light. Reason: white light is a mixture of seven colours (VIBGYOR). Each colour travels with a different speed in glass, so the refractive index of glass is different for different colours. On refraction through the prism the different colours are therefore bent through different angles with respect to the incident ray: red is bent the least and violet the most. The colours emerge along different paths and form a band of colours, the spectrum.

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2. Q62 CBSE 2026
   Name a phenomenon taking ​place ​in nature where light rays are dispersed. When, where ​and how does ​this phenomenon ​happen ​?
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   A rainbow: seen after rain, opposite the Sun, when sunlight is refracted, dispersed and internally reflected in water droplets.

   The phenomenon is the rainbow. When: it is seen just after a rain shower (or in the spray of a waterfall or fountain) while the Sun is shining, with the Sun behind the observer, usually in the morning or late afternoon when the Sun is low. Where: in the sky in the direction opposite to the Sun, formed by tiny water droplets suspended in the air in front of the observer. How: each droplet acts like a small prism. Sunlight entering it is refracted and dispersed into its colours, is reflected internally at the back of the drop, and is refracted again as it comes out. Because each colour leaves at a slightly different angle, different colours reach the eye from different drops and a spectrum is seen as an arc, red on the outside and violet on the inside.

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3. Q63 CBSE 2026
   Why is the ​concave ​lens used ​as ​a ​corrective lens ​for a ​myopic eye ?
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   A concave lens makes rays from a distant object appear to come from the far point, so the eye focuses them on the retina.

   In a myopic (near-sighted) eye the image of a distant object is formed in front of the retina, because the eye lens is too converging or the eyeball is too long, so the far point is nearer than infinity. A concave lens is a diverging lens: a concave lens of suitable power (focal length equal to minus the far-point distance) spreads out the parallel rays from a distant object so that they appear to come from the far point of the eye. The eye can focus them on the retina, so the distant object is seen clearly. That is why a concave lens is used to correct myopia.

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4. Q64 CBSE 2026
   With ​the help of ​a ray ​diagram, ​explain any ​phenomenon of ​formation of spectrum in nature.
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   A rainbow forms when raindrops disperse sunlight by refraction, internal reflection and refraction, giving a spectrum with red outside and violet inside.

   The rainbow is a natural spectrum formed after rain by the dispersion of sunlight by tiny water droplets in the atmosphere. Each droplet acts like a small prism: sunlight is refracted and dispersed as it enters the drop, reflected internally at the back surface, and refracted again as it comes out (see the ray diagram). The colours emerge at slightly different angles - red at about $42^{\circ }$, violet at about $40^{\circ }$ to the direction opposite the Sun - so an observer standing with the Sun behind sees a band of colours in the sky, red on the outside and violet on the inside, always on the side opposite the Sun.

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5. Q65 CBSE 2026
   Draw a ray diagram to show the correction of ​eye ​defect of an ​old man who can not see an object placed closer than ​1 ​m from ​his ​eye, clearly.
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   Presbyopia, corrected by a convex lens of power $+3$ D (focal length $+33$ cm).

   The old man's near point has receded to $1$ m, so he suffers from presbyopia: with age the ciliary muscles weaken and the eye lens loses its flexibility, so the near point recedes. For near vision it behaves like long-sightedness (hypermetropia) - light from a nearby object would be focused behind the retina. It is corrected with spectacles carrying a convex (converging) lens: to read at the normal $25$ cm, $\frac{1}{f}=\frac{1}{-100}-\frac{1}{-25}=\frac{3}{100}$ per cm, so $f=+\frac{100}{3}$ cm $\approx +33$ cm and $P=+3$ D. Ray diagram: the object stands at $N$ ($25$ cm); the convex lens in front of the eye bends the rays from $N$ so that they leave it diverging as if from $N^{\prime }$ ($1$ m, his near point - shown by dashed backward extensions), and the eye lens then focuses them on the retina. Arrows on every ray show the direction of light.

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6. Q66 CBSE 2026
   Match the items given ​in ​Column I ​with the correct ​option given ​in Column II ​:
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   1 - (s), 2 - (p), 3 - (q), 4 - (r). Mirror: Reflection of light; Lens: Refraction of light; Prism: Dispersion of light; Scattering of light: Tyndall effect.

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7. Q67 CBSE 2026
   A person is unable to read a book placed closer than 1 meter from his eyes. Identify ​the ​defect of vision in his ​eyes. Draw ​the ​ray ​diagrams to ​show the defect of vision and its correction.
   Show answer

   Hypermetropia, with the near point at 1 m; a convex lens makes rays from 25 cm appear to come from 1 m.

   The person suffers from hypermetropia (far-sightedness): his near point has moved from $25$ cm to $1$ m, so light from a book held closer than $1$ m is focused behind the retina. It is caused by too long a focal length of the eye lens, or by the eyeball becoming too small. It is corrected with spectacles having a convex (converging) lens of suitable power - here $f\approx +33$ cm, $P=+3$ D - which makes the rays from a book at $25$ cm appear to come from $1$ m, so the image forms on the retina. Ray diagrams: (i) The defect - rays from $N^{\prime }$ ($1$ m) meet on the retina, while rays from $N$ ($25$ cm) would meet behind it; (ii) The correction - the convex lens bends the rays from $N$ as if they came from $N^{\prime }$, and the eye focuses them on the retina.

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8. Q68 CBSE 2026
   Study the given diagram and answer ​the questions that follow :

   1. (a)Write the name of the eye defect shown in the diagram. Where is the image formed ​in this eye ​defect with respect to the ​retina ​of the eye ?
   2. (b)List ​two causes ​of this eye defect.
   3. (c)With the help of a diagram, show how this eye defect of vision is corrected.

   Show answer

   The defect is hypermetropia: the image forms behind the retina; a convex lens corrects it.

   (a) The defect is hypermetropia (far-sightedness). The image of a nearby object is formed behind the retina. (b) Two causes: the focal length of the eye lens is too long (the eye lens is not converging enough), and the eyeball has become too small. (c) It is corrected with spectacles having a convex (converging) lens of suitable power: the lens makes the rays from a nearby object at $N^{\prime }$ less divergent, so that they appear to come from the farther point $N$, the near point of this eye, and the eye lens then focuses them on the retina (see the diagram).

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9. Q69 CBSE 2026
   1. (a)Draw the ray diagram for ​refraction of light through ​a glass prism and ​mark angle of ​refraction and ​angle of deviation.
   2. (b)When the ​path ​of a light ray refracted through a glass prism is reversed how will the ​angle of deviation change ? Explain.
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   The angle of deviation remains the same, because the reversed ray retraces its path and $D=i+e-A$ depends only on $i+e$.

   (a) A ray PE falls on face AB of the prism at E and, bending towards the normal $N{N}^{\prime }$, travels through the glass along EF; at F on face AC it bends away from the normal $M{M}^{\prime }$ and emerges along FS. Marked on the diagram: the angle of refraction $\angle r$, between EF and the normal at E, and the angle of deviation $\angle D$, between the incident ray PE produced forward and the emergent ray FS produced backward (with $\angle i$, $\angle e$ and the angle of the prism $\angle A$ shown as well). (b) The angle of deviation does not change - it remains the same. By the reversibility of light the reversed ray retraces the original path, so its angle of incidence is the old angle of emergence and its angle of emergence the old angle of incidence; since $D=i+e-A$ depends only on the sum $i+e$, interchanging the two leaves the deviation unchanged.

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10. Q70 CBSE 2026
    State ​the reasons for myopia. With ​the help of a ray ​diagram, show ​the :

    1. (a)Image formation by myopic eye, ​and
    2. (b)​Correction of ​myopic eye by using an appropriate lens.
    Show answer

    Myopia arises from excessive lens curvature or an elongated eyeball; a concave lens of suitable power brings the image back onto the retina.

    Reasons for myopia: the image of a distant object is formed in front of the retina, because of (i) excessive curvature of the eye lens, which gives it too short a focal length and too much converging power, and / or (ii) elongation of the eyeball, which puts the retina too far behind the lens. The far point of the eye then lies at a finite distance instead of at infinity, so distant objects are seen blurred while near objects are seen clearly. (a) Ray diagram of the myopic eye: parallel rays from a distant object are converged by the eye lens and meet at a point in front of the retina, then spread out again and fall on the retina as a blurred patch. (b) Ray diagram of the correction: a concave (diverging) lens of suitable power is placed in front of the eye. It diverges the parallel rays so that they appear to come from the far point of the eye; the eye lens then brings them to a sharp focus on the retina. The focal length of the correcting lens equals the distance of the far point, so its power is negative — $f=-D$, $P=-1/D$.

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11. Q71 CBSE 2026
    1. (a)​State the causes of hypermetropia.
    2. (b)With the help ​of ray diagram, show the ​: (i) ​Image formation ​by hypermetropic ​eye, and (ii) Correction of hypermetropia by using an appropriate ​lens.
    Show answer

    Hypermetropia is caused by a long eye-lens focal length or a short eyeball; a convex lens corrects it.

    (a) Hypermetropia is caused by (i) a decrease in the converging power of the eye lens, that is, its focal length becoming too long, and (ii) the eyeball becoming too short, so that the distance between the eye lens and the retina is too small. Either cause makes light from a nearby object converge behind the retina, and the near point recedes beyond $25$ cm. (b)(i) The ray diagram of the defective eye shows rays from an object at the normal near point ($25$ cm) meeting at a point behind the retina, so the retina receives a blurred patch instead of a sharp image. (ii) The correction diagram shows a convex (converging) lens of suitable power placed in front of the eye: it supplies the missing convergence - equivalently, it forms a virtual image of the object at the eye's own near point - and the eye lens then brings the light to a sharp focus exactly on the retina.

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12. Q72 CBSE 2026
    (A) What ​is ​meant by presbyopia ? Write the causes of presbyopia also. (B) ​Draw ​the ray diagram ​for ​correction of presbyopia by ​using an appropriate lens.
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    Presbyopia is loss of accommodation with age, caused by weak ciliary muscles and a hardened lens; a convex lens corrects it.

    (A) Presbyopia is the defect of vision in which the power of accommodation of the eye decreases with ageing: the near point moves away from the eye, so a person cannot see nearby objects clearly and comfortably and finds reading difficult without spectacles. Its causes are the gradual weakening of the ciliary muscles, which can no longer make the eye lens thick enough for a near object, and the gradual hardening of the crystalline eye lens, which loses its flexibility. A person may suffer from both myopia and hypermetropia, and such people often require bi-focal lenses. (B) It is corrected with a convex (converging) lens of suitable power, used as reading glasses. In the ray diagram the book is placed at the normal near point, $25$ cm; the convex lens forms a virtual, erect and enlarged image of it at the receded near point $N^{\prime }$ of the eye, and the eye then focuses that image sharply on the retina. For $N^{\prime }=100$ cm the lens needed has $\frac{1}{f}=\frac{1}{-100}-\frac{1}{-25}=\frac{3}{100}$, that is $f=+33.3$ cm and $P=+3$ D.

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13. Q73 CBSE 2026
    1. (a)Explain ​the ​Tyndall effect ​with the ​help ​of one suitable ​example.
    2. (b)What happens when a white light gets scattered from (i) very fine particles (ii) larger size particles ?
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    Tyndall effect is scattering of light by colloidal particles, as in a smoke-filled room; very fine particles scatter mainly blue, larger ones longer wavelengths.

    (a) Tyndall effect: when a beam of light passes through a medium containing very small suspended (colloidal) particles, the particles scatter the light in all directions, and the path of the beam becomes visible. Example: when a fine beam of sunlight enters a smoke-filled room through a small hole, its path is seen because the smoke particles scatter the light. (Sunlight passing through the canopy of a dense forest is seen as shafts because the mist droplets scatter it.) (b) The colour of the scattered light depends on the size of the particles. (i) Very fine particles, such as air molecules, scatter mainly blue light (the shorter wavelengths), so the scattered light looks blue; this is why the clear sky is blue. (ii) Larger particles scatter light of longer wavelengths, so red light (light of longer wavelength) is seen in the scattered light. If the particles are large enough, such as the water droplets in clouds, all colours are scattered about equally and the scattered light may even appear white.

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14. Q74 CBSE 2026
    Explain the ​phenomenon of rainbow ​formation in the ​sky. ​Draw the labelled ray diagram in support of your ​explanation.
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    A rainbow forms as droplets refract and disperse sunlight, reflect it internally and refract it again, with red outside and violet inside.

    A rainbow is a natural spectrum seen in the sky after a rain shower. It is produced by the tiny water droplets left suspended in the air, each of which acts like a small prism, and it is always seen in the direction opposite to the Sun, so the observer must stand with the Sun behind and the droplets in front. Three things happen to sunlight inside one droplet: (i) it is refracted as it passes from air into the water, and since water bends violet more than red the white light is dispersed into its colours; (ii) the dispersed light reaches the inner back surface of the droplet and is reflected internally, which turns it back towards the front of the drop; (iii) it is refracted again as it leaves the droplet into the air, and this second refraction spreads the colours further apart. Because red is returned at the larger angle, about $42^{\circ }$ to the incoming sunlight, and violet at a slightly smaller angle, the droplets that send red to the eye lie higher in the sky than those that send violet, so the bow appears with red on its outer edge and violet on its inner edge. The labelled ray diagram of a single droplet, showing refraction with dispersion, internal reflection and refraction with dispersion again, accompanies this answer.

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15. Q75 CBSE 2026
    What is scattering ​of ​light ? How is scattering of light ​different from ​reflection of ​light ​? Explain.
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    Scattering sends light in all directions from tiny particles in its path; reflection turns it back from a surface in one direction.

    Scattering of light is the sending out of light in all directions by very small particles in its path - molecules of air, fine dust, smoke or colloidal particles. The colour of the scattered light depends on the size of the particles: very fine particles scatter blue light much more than red, which is why the clear sky looks blue, while larger particles scatter all colours about equally, which is why clouds look white. It differs from reflection in three ways: 1. Scattering is caused by tiny particles in the path of the light; reflection takes place at a surface, such as a mirror. 2. Scattered light spreads out in all directions; light reflected from a smooth surface leaves in one definite direction, fixed by the laws of reflection (the angle of reflection equals the angle of incidence). 3. Scattering depends on the colour (wavelength) of the light, so fine particles can separate blue from red; a mirror reflects every colour in the same direction, so a white beam stays white.

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16. Q76 CBSE 2026
    What is ​meant by atmospheric ​refraction of light ? Explain ​the following natural ​phenomenon by using the concept ​of ​atmospheric refraction :

    1. (a)​Twinkling of stars
    2. (b)Flickering of objects seen through a turbulent stream of hot air
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    Atmospheric refraction is refraction of light by the changing density of air; it makes stars twinkle and objects flicker through hot air.

    Atmospheric refraction: the refraction of light by the earth's atmosphere, whose optical density and hence refractive index decrease gradually with height and also keep changing with time, so that light passing through it is refracted continuously and travels along a curved path instead of a straight line. (a) Twinkling of stars: a star is a point source of light. Its light is refracted continuously as it comes down through the atmosphere and bends towards the normal, so the star appears a little higher than its true position. Because the physical conditions of the atmosphere are not stationary, the refractive index of the air keeps changing, the apparent position of the star goes on wavering and the amount of starlight entering the eye keeps varying — so the star appears brighter at one moment and fainter at another. That is twinkling. (b) Flickering through hot air: hot air is lighter and optically rarer than the cool air around it, and it rises in a turbulent stream, so the stream is a patchwork of refractive indices that keeps rearranging itself. Light from an object beyond it is refracted by amounts that keep changing, the rays reach the eye from slightly different directions from moment to moment, and the apparent position of the object keeps shifting — so the object appears to flicker.

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17. Q77 CBSE 2026
    1. (a)What is meant by Tyndall ​effect ?
    2. (b)​How is scattering ​of light different ​from reflection of light ?
    3. (c)What will happen if white light (sunlight) is scattered from (i) very ​small particles of medium, ​and ​(ii) very large particles of medium ?
    Show answer

    Tyndall effect is scattering by colloidal particles; scattering depends on particle size and colour, unlike reflection; small particles give blue, large give white.

    (a) The Tyndall effect is the scattering of a beam of light by the very fine, colloidal particles suspended in a medium, which makes the path of the beam visible from the side - as when sunlight enters a smoke-filled room through a small hole, or shines through the mist in a dense forest. (b) Scattering of light depends on the size of the scattering particles and on the wavelength (colour) of the light, whereas reflection of light is independent of both. In reflection the light meets a surface and is turned back into the same medium along one definite direction, obeying the laws of reflection (angle of reflection = angle of incidence), and its colour is unchanged; in scattering the light is taken up by fine particles suspended in the medium and sent out again in all directions, and very fine particles scatter mainly the shorter wavelengths, so the scattered light can differ in colour from the incident light. (c) (i) Very small particles scatter mainly the shorter wavelengths, so the scattered light appears **blue** - this is why the clear sky is blue. (ii) Very large particles scatter all wavelengths almost equally, so the scattered light appears **white** - this is why clouds and fog look white.

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18. Q78 CBSE 2026
    (A) The elderly people, may have both near sightedness and far sightedness. ​Write the possible solutions, can ​be proposed ​for correction of their eye ​defect. (B) How does the eye control the ​amount ​of light entering into it ?
    Show answer

    Bi-focal lenses or two pairs of spectacles correct both defects; the iris changes the pupil size to control the light entering the eye.

    (A) An elderly person who has both near sightedness (myopia) and far sightedness (hypermetropia) needs a concave lens for distant vision and a convex lens for near vision. The possible solutions are: (i) two separate sets of spectacles - one (concave lenses) for correcting the near sightedness and the other (convex lenses) for correcting the far sightedness; (ii) bi-focal spectacles, in which each lens has two parts: the upper portion is a **concave** lens, looked through for distant vision, and the lower portion is a **convex** lens, looked down through for reading - or progressive (varifocal) lenses, which give the two powers with a gradual change between them. Contact lenses or corrective surgery are further options. (B) The amount of light entering the eye is controlled by the **iris**, the dark muscular diaphragm behind the cornea, which changes the size of the **pupil** - the opening at its centre through which light enters. In bright light the iris contracts the pupil so that less light enters and the retina is protected; in dim light the iris widens the pupil so that more light enters. The pupil therefore acts as a variable aperture.

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19. Q79 CBSE 2026
    Two persons, A ​and B are using lenses of power $+1.5$ D and $-1.5$ ​D respectively in their spectacles. Write ​the names of eye defects from ​which A ​and ​B are ​suffering. Write two ​causes for each defect of vision.
    Show answer

    A has hypermetropia (convex lens, long eye-lens focal length or small eyeball); B has myopia (concave lens, excessive lens curvature or long eyeball).

    A (power $+1.5$ D, a convex lens) suffers from hypermetropia (long-sightedness or far-sightedness): nearby objects are not seen clearly because their image forms behind the retina. Two causes: (i) the focal length of the eye lens is too long; (ii) the eyeball has become too small. B (power $-1.5$ D, a concave lens) suffers from myopia (short-sightedness or near-sightedness): distant objects are not seen clearly because their image forms in front of the retina. Two causes: (i) excessive curvature of the eye lens, which makes its focal length too short; (ii) elongation of the eyeball.

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20. Q80 CBSE 2026
    A person is suffering from a defect of vision due to the elongation of his/her eye ball.

    1. (a)Write the name of the defect ​of vision and write the other possible ​cause of this ​defect of ​vision.
    2. (b)This defect can be ​corrected by using a ​suitable lens. Draw the ray diagram for ​correction of this defect of vision.
    Show answer

    The defect is myopia; its other cause is excessive curvature of the eye lens; a concave lens of suitable power corrects it.

    (a) The defect is myopia, also called short-sightedness or near-sightedness: the image of a distant object is formed in front of the retina, so distant objects are not seen distinctly. Besides elongation of the eye ball, the other possible cause of myopia is excessive curvature of the eye lens - a lens curved so strongly that its converging power is too great and its focal length too short. (b) The defect is corrected by placing a concave (diverging) lens of suitable power in front of the eye; its power is negative and its focal length is equal to the distance of the far point of the defective eye. In the ray diagram, rays from a distant object arrive parallel to the principal axis and fall on the concave lens; after the lens they diverge, and their dashed backward extensions meet at the far point $F$ of the defective eye, so the rays entering the eye appear to come from $F$. The eye lens then converges them to a sharp point exactly on the retina.

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