CBSE Class 10 Science — The Human Eye and the Colourful World

To restore clear vision in persons whose size of the eye ball has reduced, he/she is suggested to use suitable

When you look at an object very close to your eyes, the:

Directions: For question number 32, two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer from the codes given below. Assertion (A): When rays of white light pass through a prism, on emerging they give spectrum of seven colours. Reason (R): It is due to the scattering of light that red light bends minimum and violet light bends the maximum.

(A) (i) How does the change in curvature of the eye lens helps us in the process of seeing the nearby objects clearly? (ii) State the range of the power of accommodation of a normal human eye. OR (B) 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.

(A) (i) How does the change in curvature of the eye lens help us in the process of seeing nearby objects clearly? (ii) State the range of the power of accommodation of a normal human eye. OR (B) Draw a ray diagram to show the correction of eye defect of an old man who cannot see an object placed closer than $1\text{ m}$ from his eye, clearly.

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.

To get an image of magnification $-1$ on a screen using a lens of focal length $20\text{ cm}$, the object distance must be :

An optical device 'X' is placed obliquely in the path of a narrow parallel beam of light. If the emergent beam gets displaced laterally, the device 'X' is :

When a beam of white light passes through a region of very fine dust particles, the colour of light that scatters the most in that region is :

In order to obtain large images of the teeth of patients, the dentist holds the concave mirror in such a manner that the teeth are positioned

The possible way to restore clear vision of those people whose eyeball has elongated is the use of suitable

An old person is suffering from an eye defect caused by weakening of ciliary muscles and diminishing flexibility of the eye lens. If the defect of vision is 'a' which can be corrected by lens 'b', then 'a' and 'b' respectively are :

The part of human eye which controls the amount of light entering into it is:

Assertion (A): When ciliary muscles contract, eye lens becomes thin. Reason (R): Ciliary muscles control the power of the eye lens.

(a) Give reasons: (i) The sky appears dark to passengers flying at very high altitude. (ii) 'Danger' signal lights are red in colour. OR (b) What is a rainbow? "We see a rainbow in the sky only after the rainfall." Why?

(a) A student has difficulty in reading his textbooks but can read the blackboard clearly while sitting in the last row. Name the defect of vision the student is suffering from. List two reasons due to which this defect arises. Write the nature of the lenses required to correct this defect. OR (b) Draw a ray diagram to show the path of a ray of light falling obliquely on one of the refracting faces of a triangular glass prism and mark the angle of deviation on it.

(A) Draw a ray diagram to show the refraction of a ray of light passing through an equilateral glass prism. Mark the angle through which the emergent ray bends from the direction of the incident ray and also name it. OR (B) Name the type of lenses required by the persons for the correction of their defect of vision called presbyopia. Write the structure of the lenses commonly used for the correction of this defect giving reason for such designs.

If we want to obtain a virtual and magnified image of an object by using a concave mirror of focal length $18\text{ cm}$, where should the object be placed? Use mirror formula to determine the object distance for an image of magnification $+2$ produced by this mirror to justify your answer.

The power of a lens is $-0.25 D$. Based on this information, find out (a) The type of lens and its focal length. (b) The eye defect for which it may be used as a corrective lens. (c) The nature and size of the image formed by this lens when an object is placed between F and 2F from the optical centre of this lens.

What is a rainbow? Draw a labelled diagram to show its formation.

A person uses lenses of $+2.0 \text{ D}$ power in his spectacles for the correction of his vision. (a) Name the defect of vision the person is suffering from. (b) List two causes of this defect. (c) Determine the focal length of the lenses used in the spectacles.

(a) (i) The power of a lens 'X' is $-2.5\ D$. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens? (ii) "The value of magnification 'm' for a lens is $-2$." Using new Cartesian Sign Convention and considering that an object is placed at a distance of $20\ cm$ from the optical centre of this lens, state : (I) the nature of the image formed; (II) size of the image compared to the size of the object; (III) position of the image, and (IV) sign of the height of the image. (iii) The numerical values of the focal lengths of two lenses A and B are $10\ cm$ and $20\ cm$ respectively. Which one of the two will show higher degree of convergence/divergence? Give reason to justify your answer. OR (b) (i) Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass. (ii) State Snell's law of refraction of light. (iii) Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of : (I) object distance, and (II) magnification.

The students in a class took a thick sheet of cardboard and made a small hole in its centre. Sunlight was allowed to fall on this small hole and they obtained a narrow beam of white light. A glass prism was taken and this white light was allowed to fall on one of its faces. The prism was turned slowly until the light that comes out of the opposite face of the prism appeared on the nearby screen. They studied this beautiful band of light and concluded that it is a spectrum of white light. (i) Give any one more instance in which this type of spectrum is observed. (ii) What happens to white light in the above case? (iii) (A) List two conditions necessary to observe a rainbow. OR (iii) (B) Draw a ray diagram to show the formation of a rainbow. Mark on it, points (a), (b) and (c) as given below: (a) Where dispersion of light occurs. (b) Where light gets reflected internally. (c) Where final refraction occurs.

A person allowed a narrow beam of white light from the sun to enter a dark room through a small aperture and placed a glass prism in its path in such a manner that the beam falls on the face AB of the prism as shown in the figure. A screen S is placed on the other side of the prism, facing AC. On turning the prism slowly, a beautiful band of colours is obtained on the screen. It is the spectrum of sunlight. (a) Name the phenomenon due to which a prism splits the incident white light into a band of colours. [1] (b) State the reason of getting a band of seven colours in the above case. [1] (c) (i) Explain with the help of a labelled ray diagram, an experimental arrangement to show the recombination of the spectrum of white light. [2] OR (c) (ii) Draw a labelled ray diagram to show the formation of a rainbow. [2]

Absolute refractive index of glass and water is $\frac{3}{2}$ and $\frac{4}{3}$ respectively. If the speed of light in glass is $2 \times 10^{8} \mathrm{~m} / \mathrm{s}$, the speed of light in water is :

When a beam of white light passes through a region having very fine dust particles, the colour of light mainly scattered in that region is :

The phenomena of light involved in the formation of rainbow are :

The colour of light for which the refractive index of glass is minimum, is :

The Phenomena of light involved in the formation of a rainbow in the sky are

Assertion (A): Red light signals are used to stop the vehicles on the road. Reason (R): Red coloured light is scattered the most so as to be visible from a large distance.

When do we say that a particular person is suffering from hypermetropia? List two causes of this defect. Name the type of lens used to correct this defect.

A person suffering from presbyopia needs bifocal lens. If he needs two lens of power - 4.0 dioptre and + 2.0 dioptre, which one of these two lenses is for the correction of distant vision and what is its focal length?

Study the diagram given below and answer the questions that follow: (i) Name the defect of vision represented in the diagram. Give reason for your answer. (ii) List two causes of this defect. (iii) With the help of a diagram show how this defect of vision is corrected.

(a) Study the diagram given below and answer the questions that follow: (i) Name the defect of vision depicted in this diagram stating the part of the eye responsible for this condition. (ii) List two causes of this defect. (iii) Name the type of lens used to correct this defect and state its role in this case. OR (b) 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.

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.

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.

(a) Upper half of a convex lens is covered with a black paper. Draw a ray diagram to show the formation of image of an object placed at a distance of 2F from such a lens. Mention the position and nature of the image formed. State the observable difference in the image obtained if the lens is uncovered. Give reason to justify your answer. (b) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine the distance of the image from the optical centre of the lens.

(a) The variation of image distance (v) with object distance (u) for a convex lens is given in the following observation table. Analyse it and answer the questions that follow : | S. No. | Object distance (u) cm | Image distance (v) cm | |---|---|---| | 1 | -150 | +30 | | 2 | -75 | +37.5 | | 3 | -50 | +50 | | 4 | -37.5 | +75 | | 5 | -30 | +150 | | 6 | -15 | +37.5 | (i) Without calculation, find the focal length of the convex lens. Justify your answer. (ii) Which observation is not correct? Why? Draw ray diagram to find the position of the image formed for this position of the object. (iii) Find the approximate value of magnification for $\mathrm{u} = - 30 \mathrm{cm}$. OR (b) (i) Define principal axis of a lens. Draw a ray diagram to show what happens when a ray of light parallel to the principal axis of a concave lens passes through it. (ii) The focal length of a concave lens is $20 \mathrm{cm}$. At what distance from the lens should a $5 \mathrm{cm}$ tall object be placed so that its image is formed at a distance of $15 \mathrm{cm}$ from the lens? Also calculate the size of the image formed.

In human eye the part which allows light to enter into the eye is -

Assertion (A): A person suffering from myopia cannot see the distant objects clearly. Reason (R): A converging lens is used for the correction of myopic eye as it can form real as well as virtual images of the objects placed in front of it.

(a) When and where does a rainbow appear in the sky? Draw a labelled ray diagram to show its formation. OR (b) What is scattering of light? Why does the clear sky appear blue?

Observe the following diagram showing an image formation in an eye : (a) Identify the defect of vision shown in the figure. (b) List its two causes and suggest a suitable corrective lens to overcome this defect.

(A) Observe the following diagram and answer the questions following it : (i) Identify the defect of vision shown. (ii) List its two causes. (iii) Name the type of lens used for the correction of this defect. OR (B) The colour of clear sky from the earth appears blue but from the space it appears black. Why ?

(a) A narrow beam XY of white light is passing through a glass prism ABC as shown in the diagram: Trace it on your answer sheet and show the path of the emergent beam as observed on the screen PQ. Name the phenomenon observed and state its cause. OR (b) It is observed that the power of an eye to see nearby objects as well as far off objects diminishes with age. (i) Give reason for the above statement. (ii) Name the defect that is likely to arise in the eyes in such a condition. (iii) Draw a labelled ray diagram to show the type of corrective lens used for restoring the vision of such an eye.

(a) (i) An object of $5\mathrm{cm}$ height is placed at a distance of $20\mathrm{cm}$ from the optical centre of a concave lens of focal length $18\mathrm{cm}$. Calculate (1) image distance and (2) the magnification in this case. (ii) Compare the values of magnification obtained by a concave lens and a convex lens when both the lenses form virtual images. OR (b) A convex lens can form a (i) real, inverted and magnified image as well as (ii) virtual, erect and magnified image of an object. If the focal length of the lens is $10\mathrm{cm}$, what should be the range of the object distance in both cases? Draw ray diagrams to justify your answer.

(A) Define the following terms in the context of a diverging mirror: (i) Principal focus (ii) Focal length Draw a labelled ray diagram to illustrate your answer. OR (B) An object of height $10 cm$ is placed $25 cm$ away from the optical centre of a converging lens of focal length $15 cm$. Calculate the image-distance and height of the image formed.

(a) State one important function of the following parts of the human eye: (i) Retina (ii) Pupil (b) State the role of ciliary muscles in focussing objects at varying distances from the eye.

The power of a lens is $+4D$. Find the focal length of this lens. An object is placed at a distance of $50 cm$ from the optical centre of this lens. State the nature and magnification of the image formed by the lens and also draw a ray diagram to justify your answer.

State reasons for Myopia. With the help of ray diagrams, show the (a) image formation by a myopic eye, and (b) correction of myopia using an appropriate lens.

Give reasons for the following: (a) Danger signals installed at airports and at the top of tall buildings are of red colour. (b) The sky appears dark to the passengers flying at very high altitudes. (c) The path of a beam of light passing through a colloidal solution is visible.

Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses $\mathrm{P}_1, \mathrm{P}_2, \mathrm{P}_3 \ldots$ as $\mathrm{P} = \mathrm{P}_1 + \mathrm{P}_2 + \mathrm{P}_3\ldots$ This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses. (a) What is the nature (convergent / divergent) of the combination of a convex lens of power $+4 \mathrm{D}$ and a concave lens of power $-2 \mathrm{D}$ ? (b) Calculate the focal length of a lens of power $-2 \cdot 5 \mathrm{D}$ . (c) Draw a ray diagram to show the nature and position of an image formed by a convex lens of power $+0 \cdot 1 \mathrm{D}$ , when an object is placed at a distance of $20 \mathrm{cm}$ from its optical centre. OR (c) How is a virtual image formed by a convex lens different from that formed by a concave lens? Under what conditions do a convex and a concave lens form virtual images?

The ability of a medium to refract light is expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density. On comparing two media, the one with the large refractive index is optically denser medium than the other. The other medium with a lower refractive index is optically rarer. Also the speed of light through a given medium is inversely proportional to its optical density. (i) Determine the speed of light in diamond if the refractive index of diamond with respect to vacuum is 2.42. Speed of light in vacuum is $3 \times 10^8 m/s$. (1 mark) (ii) Refractive indices of glass, water and carbon disulphide are 1.5, 1.33 and 1.62 respectively. If a ray of light is incident in these media at the same angle (say $\theta$), then write the increasing order of the angle of refraction in these media. (1 mark) (iii) (A) The speed of light in glass is $2 \times 10^8 m/s$ and in water is $2.25 \times 10^8 m/s$. (a) Which one of the two is optically denser and why? (b) A ray of light is incident normally at the water-glass interface when it enters a thick glass container filled with water. What will happen to the path of the ray after entering the glass? Give reason. (2 marks) OR (iii) (B) The absolute refractive indices of water and glass are $4/3$ and $3/2$ respectively. If the speed of light in glass is $2 \times 10^8 m/s$, find the speed of light in (i) vacuum and (ii) water. (2 marks)

The sky appears dark to passengers flying at very high altitudes mainly because:

Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset: A. Light from the sun near the horizon passes through thinner layers of air. B. Light from the sun covers larger distance of the earth's atmosphere before reaching our eyes. C. Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles. D. Light from the sun near the horizon passes through thicker layers of air. The correct reasons are

Person suffering from cataract has

The image distance from the eye lens in the normal eye when we increase the distance of an object from the eye

(a) List two causes of hypermetropia. (b) Draw ray diagrams showing (i) a hypermetric eye and (ii) its correction using suitable optical device.

OR: (a) State the relation between colour of scattered light and size of the scattering particle. (b) The apparent position of an object, when seen through the hot air, fluctuates or wavers. State the basic cause of this observation. (c) Complete the path of white light when it passes through two identical prisms placed as shown:

(a) With the help of labelled ray diagram show the path followed by a narrow beam of monochromatic light when it passes through a glass prism. (b) What would happen if this beam is replaced by a narrow beam of white light ? OR (a) A person is suffering from both myopia and hypermetropia. (i) What kind of lenses can correct this defect ? (ii) How are these lenses prepared ? (b) A person needs a lens of power + 3D for correcting his near vision and - 3D for correcting his distant vision. Calculate the focal lengths of the lenses required to correct these defects.

A student uses spectacles of focal length $-2.5 \text{ m}$. (a) Name the defect of vision he is suffering from. (b) Which lens is used for the correction of this defect? (c) List two main causes of developing this defect. (d) Compute the power of this lens.

OR Give reasons: (a) Red colour is selected for danger signals. (b) The sky appears dark in space. (c) The time difference between actual sunset and apparent sunset is about 2 minutes.

Define the term power of accommodation. Write the modification in the curvature of the eye lens which enables us to see the nearby objects clearly?

State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms, show that white light is made of seven colours? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination.

What is “dispersion of white light”? Draw a labelled diagram to illustrate the recombination of the spectrum of white light. Why is it essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other?

(a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain (i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes. (ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens. (b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention.

Study the following ray diagram: In this diagram, the angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by

Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device.

The image of an object formed by a mirror is real, inverted and is of magnification – 1. If the image is at a distance of 40 cm from the mirror, where is the object placed? Where would the image be if the object is moved 20 cm towards the mirror? State reason and also draw ray diagram for the new position of the object to justify your answer.

The image formed by a spherical mirror is real, inverted and is of magnification $-2$. If the image is at a distance of 30 cm from the mirror, where is the object placed? Find the focal length of the mirror. List two characteristics of the image formed if the object is moved 10 cm towards the mirror.

(i) What should be the range of distance of an object placed in front of the mirror? (ii) Will the image be smaller or larger than the object. Draw ray diagram to show the formation of image in this case. (iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror? Draw ray diagram for this situation also to justify your answer. Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.

What is atmospheric refraction? Use this phenomenon to explain the following natural events. (a) Twinkling of stars (b) Advanced sun-rise and delayed sun-set. Draw diagrams to illustrate your answers.

(a) Define focal length of a divergent lens. (b) A divergent lens of focal length 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use lens formula to determine the distance of the object from the lens and the size of the image formed. (c) Draw a ray diagram to show the formation of image in the above situation.

With the help of a labelled diagram, explain why the sun appears reddish at the sun-rise and the sun-set.

A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect. Draw ray diagram for the: (i) defect of vision and also (ii) for its correction.

After tracing the path of a ray of light through a glass prism a student marked the angle of incidence ($\angle i$), angle of refraction ($\angle r$) angle of emergence ($\angle e$) and the angle of deviation ($\angle D$) as shown in the diagram. The correctly marked angles are:

State the difference in colours of the sun observed during sunrise/sunset and noon. Give explanation for each.

(a) A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length. (b) We see advertisements for eye donation on television or in newspapers. Write the importance of such advertisements.

While performing the experiment to trace the path of a ray of light passing through a glass prism, four students marked the incident ray and the emergent ray in their diagrams in the manner shown below. The correct path of the rays has been shown by:

In an experiment to trace the path of a ray of light through a glass prism for different values of angle of incidence a student would find that the emergent ray:

State one function of the crystalline lens in the human eye.

State one function of iris in human eye.

Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.

Draw a ray diagram to show the formation of a rainbow and mark the point where (i) dispersion, (ii) internal reflection occurs.

A star appears slightly higher (above) than its actual position in the sky. Illustrate it with the help of a labelled diagram.

“The time difference between the actual sunset and the apparent sunset is about 2 minutes.” What is the reason for the same? Explain with the help of a diagram.

A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected ? Draw ray diagrams for the (i) defect of vision and also (ii) for its correction.

Draw a diagram to show why distant objects cannot be seen distinctly by a myopic eye. List two reasons due to which this defect of vision may be caused. A person with a myopic eye cannot see objects clearly beyond a distance of 2 m. Name the type of the corrective lens that would be needed to correct the defect of vision and draw a ray diagram to show how the defect gets corrected.

Why is the colour of clear sky blue ?

What is Tyndall effect?

What is meant by the dispersion of white light? Draw a diagram to show dispersion of white light by the glass prism.

Explain the formation of rainbow in the sky with the help of a diagram.

Give reasons : (i) The extent of deviation of a ray of light on passing through a glass prism depends on its colour. (ii) Lights of red colour are used for danger signals.

What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.

Name the three common defects of vision. What are their causes ? Name the type of lens used to correct each of them.

What eye defect is myopia ? Describe with a neat diagram how this defect of vision can be corrected by using a suitable lens.

Name the part of our eyes that helps us to focus near and distant objects in quick succession.

In the figure given below a narrow beam of white light is shown to pass through a triangular glass prism. After passing through the prism it produces a spectrum XY on a screen. (a) State the colour seen at X and Y. (b) Why do different colours of white light bend through different angles with respect to the incident beam of light?