Class 10 Science · Chapter 10

The Human Eye and the Colourful World

281 Class 10 Science questions on The Human Eye and the Colourful World from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 8 of 15

1. Q141 CBSE 2024
   Name the ​phenomenon of light responsible ​for ​Tyndall effect. Write an event where this ​phenomenon ​can be ​observed.
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   Scattering of light; a sunlight beam entering a smoke-filled room through a small hole is seen as a bright streak.

   The phenomenon is scattering of light: fine (colloidal) particles in the path of a beam scatter the light in all directions, so the path of the beam becomes visible. Event: when a fine beam of sunlight enters a smoke-filled room through a small hole, its path is seen as a bright streak. The same effect is seen when sunlight passes through the canopy of a dense forest, where tiny water droplets in the mist scatter the light.

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2. Q142 CBSE 2024
   What ​would have ​been the colour ​of ​the sky, if the Earth had ​no atmosphere ​? Give ​reason to justify your answer.
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   The sky would appear dark (black), because with no atmosphere nothing would scatter sunlight towards us.

   The sky would appear dark (black). The sky looks blue only because the molecules of air and other fine particles in the atmosphere scatter sunlight, blue light most strongly, towards our eyes from all directions. With no atmosphere there would be nothing to scatter the sunlight, so no light would reach us from the sky except directly from the Sun, and the sky would look dark.

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3. Q143 CBSE 2024
   A person suffering ​from ​an ​eye defect uses lenses of ​power $-1$ D. ​Name the ​defect of ​vision and list ​its two causes. State the nature (converging/diverging) of the corrective lens.
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   Myopia; caused by an over-curved eye lens or an elongated eyeball; corrected by a concave (diverging) lens.

   The defect is myopia (near-sightedness). Its two causes are (i) excessive curvature of the eye lens and (ii) elongation of the eyeball. The corrective lens has $f=\frac{1}{P}=-1$ m, so it is a concave, that is diverging, lens.

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4. Q144 CBSE 2024
   The far point ​of ​a defective eye is nearer than infinity.

   1. (i)​Identify the ​defect of vision.
   2. (ii)List two possible ​causes responsible for this ​defect.
   3. (iii)Name the type of lens (converging/diverging) used for the correction ​of this ​defect.
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   Myopia; caused by excessive lens curvature or an elongated eyeball; corrected by a diverging (concave) lens.

   (i) The defect is myopia (near-sightedness). (ii) Causes: excessive curvature of the eye lens; elongation of the eyeball. (iii) A diverging lens, that is, a concave lens of suitable power.

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5. Q145 CBSE 2024
   Draw ​a ray diagram to show the formation of a rainbow ​in the sky. Mark on the ​diagram three points A, B ​and C as given below : A – where dispersion of ​light occurs B – where internal reflection of dispersed ​light occurs C – where refraction of dispersed light occurs
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   At A the ray is refracted and dispersed on entering the drop, at B internally reflected, at C refracted again on leaving.

   A ray of sunlight (white light) falls on a spherical raindrop. A is the point where it enters the drop: it is refracted and dispersed into its colours, violet bending most and red least. B is the point on the back surface of the drop where the dispersed light is reflected internally. C is the point on the front surface, lower down, where the dispersed light is refracted again as it passes out of the drop. The colours emerge separated and travel towards the observer, who has the Sun behind, and are seen as a rainbow.

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6. Q146 CBSE 2024
   What ​is presbyopia ? Name the type of ​lenses used for ​the correction ​of ​this defect. State the nature ​(converging/diverging) of ​the upper part of such lenses.
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   An age-related loss of accommodation; corrected by bifocal lenses whose upper part is concave (diverging).

   Presbyopia is the defect in which the power of accommodation of the eye decreases with age: the near point recedes and nearby objects cannot be seen clearly without glasses, because the ciliary muscles weaken and the eye lens becomes less flexible. It is corrected with bifocal lenses. The upper part of a bifocal lens is concave, that is diverging, and helps distant vision; the lower part is convex and helps near vision.

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7. Q147 CBSE 2024
   “The ​colour ​of ​the ​clear sky ​from the ​earth appears blue but the sky appears dark to ​the passengers flying ​at very high altitudes.” Explain.
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   Scattered blue light makes the sky blue; at high altitude there is too little air to scatter light, so the sky looks dark.

   From the earth, the clear sky looks blue because the molecules of air and other fine particles in the atmosphere, being smaller than the wavelength of visible light, scatter blue light (shorter wavelength) much more strongly than red light; this scattered blue light enters our eyes. At very high altitudes there is hardly any air to scatter sunlight, so scattering is not prominent and very little scattered light reaches the passengers' eyes: the sky appears dark.

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8. Q148 CBSE 2024
   Name the ​muscles ​present ​in ​the human eye which enable ​it to focus on objects at varied distances ​(i.e., distant ​as well as nearby objects). Explain how it happens.
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   The ciliary muscles change the lens curvature: they relax for distant objects (thin lens) and contract for near ones (thick lens).

   The ciliary muscles. They hold the eye lens, which is made of a flexible, jelly-like material, and change its curvature and hence its focal length. For a distant object the ciliary muscles relax: the lens becomes thin, its focal length increases, and the distant object is focused on the retina. For a nearby object the ciliary muscles contract: the curvature of the lens increases and it becomes thicker, its focal length decreases, and the nearby object is focused on the retina. This ability of the eye lens to adjust its focal length is called accommodation.

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9. Q149 CBSE 2024
   When and where does a rainbow appear in the sky ? ​List ​the phenomena of light in ​proper sequence which occurs during ​the formation ​of a rainbow. Why can a rainbow not be ​seen from the ​surface of the moon ?
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   A rainbow forms after rain, opposite the Sun; the moon has no atmosphere, hence no water droplets and no rainbow.

   A rainbow appears in the sky after a rain shower, when the Sun is shining and tiny water droplets are still present in the atmosphere. It is always seen in the direction opposite to the Sun, that is, with the Sun behind the observer. The phenomena, in sequence: (1) Refraction of sunlight, with dispersion into its colours, as it enters a water droplet; (2) Internal reflection of the light at the back surface of the droplet; (3) Refraction again, with further dispersion, as the light comes out of the droplet towards the observer. A rainbow cannot be seen from the surface of the moon because the moon has no atmosphere, so there are no water droplets suspended above it to refract, disperse and internally reflect the sunlight.

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10. Q150 CBSE 2024
    Study the diagram ​given below ​and answer the questions that follow :

    1. (i)Name the ​defect of vision represented in the ​diagram. Give ​reason for your answer.
    2. (ii)List two causes of this ​defect.
    3. (iii)With the help of a diagram show how this ​defect of ​vision is corrected.

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    Hypermetropia, caused by a long eye-lens focal length or a small eyeball, is corrected by a convex lens.

    (i) Hypermetropia (far-sightedness). Reason: the rays of light from the nearby point N′ are brought to a focus at a point behind the retina, as the dashed lines show, so a nearby object is not seen distinctly; such an eye sees distant objects clearly. (ii) Causes: (1) The focal length of the eye lens is too long. (2) The eyeball has become too small. (iii) It is corrected by using a convex (converging) lens of appropriate power. The convex lens makes the rays from the nearby object N′ appear to come from the farther point N, which the eye can focus, so the image forms on the retina (see the diagram).

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11. Q151 CBSE 2024
    Name ​and explain the phenomenon ​of light due to which the path of a beam of light becomes visible when it enters a ​smoke filled room through a small hole. Also state the dependence ​of colour of ​the light we receive ​on the ​size of the ​particle of the medium through which the beam of light passes.
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    Tyndall effect: smoke particles scatter the beam, making its path visible; fine particles scatter mainly blue, larger ones longer wavelengths.

    The phenomenon is the Tyndall effect, the scattering of light by colloidal particles. The smoke in the room consists of very fine particles; when the beam entering through the hole strikes them, they scatter the light in all directions. Part of this scattered light reaches our eyes from every point along the beam, so its path becomes visible. The colour of the scattered light depends on the size of the particles: very fine particles scatter mainly blue light, larger particles scatter light of longer wavelengths, and if the particles are large enough the scattered light may even appear white.

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12. Q152 CBSE 2024
    Define the term power of accommodation ​of human eye. What happens to the image distance in the eye when ​we increase the ​distance ​of an object from the eye ? Name and explain the role ​of the part ​of human eye ​responsible for it in this case.
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    Power of accommodation is the eye lens's ability to change its focal length; image distance stays fixed as the ciliary muscles relax.

    Power of accommodation: the ability of the eye lens to adjust its focal length (by changing its curvature) so that we can see both nearby and distant objects clearly. When the object is moved farther from the eye, the image distance does not change — the image is still formed on the retina, whose distance from the eye lens is fixed; instead, the focal length of the eye lens changes. The part responsible is the ciliary muscles, which hold the eye lens and change its curvature. As the object moves away, the ciliary muscles relax, the eye lens becomes thinner and its focal length increases, so the image is still focused sharply on the retina.

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13. Q153 CBSE 2024
    Define the term power of accommodation of human eye. Write the name of the part of eye which ​plays ​a major role in the process ​of accommodation ​and ​explain what happens ​when human eye focuses

    1. (i)nearby objects and ​
    2. (ii)distant ​objects.
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    Power of accommodation is the eye lens's ability to change focal length; the ciliary muscles contract for near objects and relax for distant ones.

    Power of accommodation is the ability of the eye lens to adjust its focal length so that both nearby and distant objects are focused on the retina. The ciliary muscles play the major role: they change the curvature, and hence the focal length, of the flexible eye lens. (i) Nearby objects: the ciliary muscles contract, the curvature of the eye lens increases and it becomes thicker, so its focal length decreases and the image of the nearby object forms on the retina. (ii) Distant objects: the ciliary muscles relax, the eye lens becomes thin, so its focal length increases and the image of the distant object forms on the retina.

    Step-by-step solution →
14. Q154 CBSE 2024
    Study the diagram given below and answer the questions that follow :

    1. (i)Name the defect of vision ​depicted in this diagram stating the part of the eye responsible ​for this condition.
    2. (ii)List two causes of this defect.
    3. (iii)​Name ​the type of lens used ​to correct this defect ​and state ​its ​role in this case.

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    Hypermetropia arises when the eye lens has too long a focal length (or the eyeball is too small); a convex lens adds converging power.

    (i) The defect is hypermetropia (far-sightedness): light from the nearby point N′ is brought to a focus behind the retina. The part of the eye responsible is the eye lens, whose focal length has become too long (an eyeball that has become too small has the same effect). (ii) Two causes: (1) the focal length of the eye lens is too long; (2) the eyeball has become too small. (iii) A convex (converging) lens of suitable power. It provides the additional converging power needed: it bends the rays from a nearby object so that they appear to come from a farther point that the eye can focus, so the image is formed on the retina.

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15. Q155 CBSE 2024
    Draw a ray ​diagram to show the formation of ​a ​rainbow in the sky. On this diagram mark A – where dispersion of light occurs, ​B ​– where internal reflection of ​light occurs and C – where refraction of light occurs. List two ​necessary conditions ​to observe a rainbow.
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    The ray is refracted and dispersed at A, internally reflected at B and refracted at C; the Sun must be behind the observer.

    Ray diagram: a ray of white sunlight enters the upper part of a raindrop; at A it is refracted and dispersed into its colours (violet bent the most, red the least); the coloured rays are reflected internally at the back of the drop at B; they are refracted again at C as they leave the drop and travel towards the observer. Two necessary conditions to observe a rainbow: (1) the Sun must be behind the observer, since a rainbow is always formed in the direction opposite to the Sun; (2) water droplets, such as raindrops just after a rain shower, must be present in the air in front of the observer.

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16. Q156 CBSE 2024
    What ​is ​dispersion ​of white light ? ​State its ​cause. Draw a diagram to show ​dispersion of a ​beam of white ​light by a glass prism.
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    Dispersion is the splitting of white light into VIBGYOR, because the refractive index of glass differs for each colour.

    Dispersion is the splitting of white light into its component colours, violet, indigo, blue, green, yellow, orange and red (VIBGYOR), when it passes through a glass prism; the band of colours obtained is called a spectrum. Cause: the different colours of light bend through different angles with respect to the incident ray as they pass through the prism, because the refractive index of glass (and so the speed of light in glass) is different for different colours; red bends the least and violet the most, so the colours emerge along different paths and separate. Diagram: a beam of white light entering one face of the prism bends towards the normal and starts to split; at the second face the colours bend away from the normal and fall on a screen as a spectrum, with red least deviated and violet, nearest the base, most deviated.

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17. Q157 CBSE 2024
    A narrow beam, PQ of white ​light is passing through a ​glass ​prism ABC as shown in the diagram. Draw a ray diagram to show the emergent ​beam as it falls on the ​screen DE. Also write the phenomenon involved and its cause. Using the second law of refraction state which colour of light must have the highest value of ​refractive index amongst seven visible colours of ​light. ​Justify your answer.

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    Dispersion of white light; violet has the highest refractive index because, for the same angle of incidence, it has the smallest angle of refraction.

    Ray diagram: at face AB the white beam PQ splits into seven colours inside the prism; on leaving face AC every colour is deviated towards the base BC, red the least and violet the most, so a spectrum forms on the screen DE with red nearest D and violet nearest E. Phenomenon: dispersion of white light. Cause: the different colours bend through different angles with respect to the incident beam, because glass has a different refractive index for each colour. Violet has the highest refractive index: for the same angle of incidence $i$ at face AB, violet has the smallest angle of refraction $r$, so $n=\sin i/\sin r$ is the greatest for violet.

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18. Q158 CBSE 2024
    Define the term dispersion ​of white light. State the colour of light which bends ​

    1. (i)the least,
    2. (ii)the most, while passing ​through a glass ​prism. Also, state the cause of dispersion of a narrow ​beam ​of white light when it passes through ​a prism.
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    Dispersion is the splitting of white light into colours; red bends the least and violet the most.

    Dispersion: the splitting of white light into its component colours (violet, indigo, blue, green, yellow, orange and red) when it passes through a prism. (i) Red light bends the least. (ii) Violet light bends the most. Cause: light of different colours travels through glass with different speeds, so the refractive index of glass is different for each colour (smallest for red, largest for violet). The colours are therefore refracted through different angles with respect to the incident ray, emerge along different paths and become separated.

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19. Q159 CBSE 2024
    When ​and where does ​a rainbow ​appear in the sky ? Write ​sequence-wise the phenomena of light responsible for the formation of a ​rainbow. List two essential ​conditions ​for observing a rainbow.
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    A rainbow forms after rain, opposite the Sun, by refraction with dispersion, internal reflection and refraction again in water droplets.

    When and where: a rainbow appears in the sky after a rain shower, when the Sun is shining and tiny water droplets are still present in the atmosphere; it is always formed in the direction opposite to that of the Sun. Phenomena, in sequence: (1) refraction of sunlight as it enters a raindrop, which also disperses it into its colours; (2) internal reflection of the light at the back surface of the drop; (3) refraction of the light again as it comes out of the drop. Two essential conditions: (1) the Sun must be behind the observer; (2) there must be tiny water droplets in the air in front of the observer, as after rain or in the spray of a waterfall or a fountain.

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20. Q160 CBSE 2024
    Draw a ray diagram to show the refraction ​of a ray of light through a triangular glass prism and mark on it ​

    1. (i)angle of incidence ($i$),
    2. (ii)angle of emergence ($e$), and
    3. (iii)angle of deviation ($D$). What would ​happen, if instead of a ray, a beam ​of white light falls on the ​prism ? ​Give reason ​for the phenomenon that occurs in this case.
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    Draw the ray through the prism marking $i$, $e$ and $D$; white light disperses into a spectrum because colours bend by different angles.

    Ray diagram: a ray PE falls on the first face of the prism at E, bends towards the normal and travels along EF inside the glass, then bends away from the normal at F on the second face and emerges along FS. The angle of incidence $i$ is the angle between PE and the normal at E, the angle of emergence $e$ is the angle between FS and the normal at F, and the angle of deviation $D$ is the angle between the incident ray produced forwards and the emergent ray produced backwards. If a beam of white light falls on the prism, it splits into a band of seven colours, violet, indigo, blue, green, yellow, orange and red (a spectrum): this is dispersion. It happens because the different colours of white light bend through different angles with respect to the incident ray as they pass through the prism, red the least and violet the most, so each colour emerges along a different path.

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