# CBSE Class 10 Physics Human Eye Colorful World Worksheet A

Read and download free pdf of CBSE Class 10 Physics Human Eye Colorful World Worksheet A. Students and teachers of Class 10 Science can get free printable Worksheets for Class 10 Science Chapter 11 Human Eye and Colourful World in PDF format prepared as per the latest syllabus and examination pattern in your schools. Class 10 students should practice questions and answers given here for Science in Class 10 which will help them to improve your knowledge of all important chapters and its topics. Students should also download free pdf of Class 10 Science Worksheets prepared by school teachers as per the latest NCERT, CBSE, KVS books and syllabus issued this academic year and solve important problems with solutions on daily basis to get more score in school exams and tests

## Worksheet for Class 10 Science Chapter 11 Human Eye and Colourful World

Class 10 Science students should refer to the following printable worksheet in Pdf for Chapter 11 Human Eye and Colourful World in Class 10. This test paper with questions and answers for Class 10 will be very useful for exams and help you to score good marks

### Class 10 Science Worksheet for Chapter 11 Human Eye and Colourful World

Question :  Match the following with correct response.
a. 1-A, 2-C, 3-B, 4-D
b. 1-D, 2-A, 3-C, 4-B
c. 1-B, 2-D, 3-A, 4-C
d. 1-C, 2-B, 3-D, 4-A
Explanation: Power of accommodation: The ability of the eye to focus both near and distant objects, by adjusting the focal length of the eye lens, is called the accommodation of the eye Near point: It is 25cm for normal eye. The minimum distance at which object can be seen most distinctly without strain.
Far point: It is infinity for normal eye. It is the farthest point upto which the eye can see object clearly.
Least distance of distinct vision in old people: As the person grows old, his ciliary muscle responsible for adjusting the eye lens gets weakened. As a result the power of accommodation reduces and hence the least distance of distinct vision for old people generally increases.

Question :  A ray of light travelling in air fall obliquely on the surface of a calm pond. It will-
a. Turn back on its original path.
b. Go into water without deviating from its path
c. Deviate towards the normal
d. Deviate away from the normal.
Explanation: When ray of light enters from a rarer medium (air) into a denser medium (water), it bends towards normal at the point of incidence.

Question : How long does the light from an event stay in our eye?
a. of a second
b. of a second
c. of a second
d. None of these
Explanation: The image of an object seen persists on the retina for 1/16 second even after the removal of the object. This continuance of sensation of eye for some time is called persistence of vision.

Question :  The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to
a. Presbyopia
b. Near-sightedness
c. Accommodation
d. Far-sightedness
Explanation: The ability of the eye to focus both near and distant objects, by adjusting the focal length with the help of ciliary muscles, is called the accommodation of the eye.

Question :  Optical fibre is used for
a. All of these
b. biomedical engineering
c. communication over long distance
d. medical applications
Explanation: Applications of optical fiber include:
i. Communication: Telephone transmissoin method usese fiber-optic cables. Optical fibres transmit energy in the form of light pulses.
ii. Medical uses: Optical fibres are well suited for medical use. They can be made in extremely thin, flexible stands for insertion into the blood vessels, lungs, and other hollow parts of the body. Optical fibers are used in a number of instruments that enable doctors to view internal body parts without having to perform surgery.
iii. Simple uses: The simplest application of optical fibers is the trnsmission of light to locations otherwise hard to reach.

CASE STUDY

1.A prism is a transparent refracting medium bounded by two plane surfacesinclined to each other at a certain angle. The refraction of light through a prism follows the laws of refraction. In the prism, refraction takes place on its refracting surface it means when the light enters the prism and when the light leaves the prism. The refraction through a prism is shown. Here, <A is the angle of prism, ∠ i is the angle of incidence of the face AB and ∠e is th

The incident ray suffers a deviation or bending through an angle δ due tothe refraction through prism. This angle is called angle of deviation as shown in figure.
i + e = δ + A

Question : The angle between the two refracting surfaces of a prism is called
(a) angle of prism
(b) angle of incidence
(c) angle of deviation
(d) angle of emergence

Question : The angle between the incident ray and the emergent ray is called
a) angle of emergence
(b) angle of deviation
(c) angle of incidence
(d) none of these

Question : When a ray is refracted through a prism, then
(a) ∠ ∠δ
(b) ∠ i=∠e+∠δ
(c) ∠δ= ∠e
(d) ∠i > ∠r

Question : The angle of deviation depends on
(a) refractive index of prism
(b) angle of incidence
(c) both (a) and (b)
(d) none of these

Question : What would have been the colour of sky if the earth had no atmosphere?
Answer :  The sky would have looked dark if the earth had no atmosphere as there would not have been any scattering.

Question : Which great scientist was colour blind?
Answer : Dalton was colour blind.

Question : On what factor does colour of scattered light depend?
Answer :  The colour of scattered light depends on the size of the scattering particle. Very fine particles scatter mainly blue light whereas particles of larger size scatter light of longer wavelengths.

Question : Why is a small amount of sodium thiosulphate added to water in tank in the activity to understand reddish appearance of sun at sunrise and sunset?
Answer :  Sodium thiosulphate is added to water in the tank for precipitating minute colloidal sulphur particles which scatter short wavelengths of light.

Question :  A man is wearing glasses of focal length +1m, what can be defect in the eye?
Answer : As the focal length of glasses is positive, so the power of the lens is also positive which indicates the use of a convex lens. Hence, he is suffering from hypermetropia.

Question :  Why are danger light signals red in color?
Answer : As red light is scattered the least and it covers longer distances. That's why it is used in danger signal.

Question : Which part of the human eye helps in changing the thickness of lens?

Question : Name the light sensitive part of the eye where image of an object is formed.

Question : Which is the range of vision of normal eye?
Answer : 25 cm to infinity.

Question : What are light sensitive cells?

Question : What type of image is formed on the retina?

Question : Define least distance of distinct vision.
Answer : The minimum distance at which the objects can be seen clearly without any strain is called least distance of distinct vision. It is the near point of eye and is equal to 25 cm.

Question : What is spectrum?
Answer : The band of seven colours obtained due to the dispersion of white light is called spectrum.

Question : What is Tyndall effect?
Answer : Scattering of light in the nature due to small particles present in the atmosphere is called Tyndall effect.

Question : Define the power of accommodation of human eye.
Answer : The ability of eye to see nearby as well as far off objects at the same time is called power of accommodation.

Question : Name the disease in which crystalline lens of human eye becomes opaque.

Question : What is the diameter of human eye?

Question : In which type of eye defect far point of the eye gets reduced?

Question : What type of lens should be used to correct the presbyopia?
Answer : Bi-focal lens. Concave-convex lens.

Question : In a human eye, name the following parts.
i. A thin membrane which allows light to enter into the eye?
ii. The muscles which help in changing the focal length of the eye lens?
Answer : i. Cornea is the thin transparent membrane.
ii. Ciliary muscles help in changing the focal length of the eye lens.

Question : The image formed on retina is inverted but we see the object erect. Why?
Answer : The image formed on retina is inverted, this image is formed on the light sensitive cells called rods and cones of the retina which generates electrical signals. This signal reaches brain via optic nerve. It is the brain that interprets this image and while processing the image it helps in perceiving objects as they are.

Question : Why danger signals are red?
Answer : Danger signals are of red colour, as it scatters the least and can be seen from the maximum distance.

Question : Why does sky look blue on a clear day?
Answer : White light scatters due to atmospheric refraction. White light is made up of seven colours out of which, blue light scatters the most hence the sky looks blue.

Question : Why do you take time to see objects when you enter a dim lighted room from outside in the sun?
Answer : In the sun light the size of pupil, is small but when one enters the dim light, it takes some time for iris to adjust the size of pupil and the light sensitive cells take some time to get activated.

Question : When white light enters the prism, which colour of light deviates/bends the least and which colour bends the most?
Answer : The light that bends the least is red colour and the light that bends the maximum is violet colour light.

Question : Why can’t we see object very close to our eye?
Answer : The objects are seen only when the image forms on retina when the light rays pass through the lens. The lens has its fixed ability of changing the focal length with the help of ciliary muscles.
Ciliary muscles cannot be contracted beyond a certain limit to change the focal length of eye lens. The objects kept very close to our eye cannot be focused by ciliary muscles.

Question : Why does a ray of light splits into different colours on passing through a glass prism?
Answer : When light rays enter the glass prism the angle at which it bends makes the light split into its seven components because the speed of each component of light is different and due to the bending every component shows its different ability to pass through it.

Question : Why do birds fly back to their nest in the evening?
Answer : Birds lack light sensitive cells called rods, due to lack of these cells they cannot see the objects clearly in less/dim light.

Question : In dispersion of white light through prism, which colour deviates most and which colour the least? Why do they deviate differently?
Answer : The colour of light that deviates least is red and violet deviates the maximum. The difference in deviation is due to the difference in wavelength and speed of each colour of light, also due to different bending ability when it passes through the prism.

Question : What is hypermetropia? How can it be corrected?
Answer : Hypermetropia is an eye defect also called as long-sightedness. Person can see a far off objects but cannot see nearby objects. It is because the image is formed beyond retina.
Cause – (a) The focal length of the eye lens is too long.
(b) The eyeball has become too small.
Correction: It can be corrected by using convex lens of appropriate power.

Question : What is the direction of rainbow formation? What is the position of red colour in rainbow?
Answer : Rainbow is always formed in the direction opposite to sun. The position of red colour in the rainbow is at the top.

Question : A short-sighted person cannot see clearly beyond 5 cm. Calculate the power of lens required to correct his vision to normal?
Answer : f = – 5 cm
P= 1/f = −(1/5)
= 0.20
∴ Power = 0.2 Dioptre

Question : Why are two eyes more helpful for us to see as compared to one?
Answer : Two eyes are more helpful as one eye gives only a view of 150° angle where as two eyes increase the view by making it wide to 180° angle. Two eyes also helps us to see the objects in dim light or darkness clearly. Two eyes give stereoscopic vision helping us assess the depth of vision.

Question : Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect?
Assume that the near point of the normal eye is 25 cm.

Question : What is accommodation?
Answer :  Accommodation is the distance between near point and far point. The eye is able to adjust its focal length in such a way that it is able to focus any of the objects between near point and far point.

Question : State one effect produced by the scattering of light by the atmosphere.
Answer :  There are two effects produced due to scattering of light in the atmosphere: tyndall effect and appearance of the blue colour of the sky. Related Theory  When light moves from one medium to another, the light scatters in different directions due to change in the medium. This is called scattering of light. When tiny particles of dust come in front of light and leads to its scattering, this is called tyndall effect. We can see these tiny dust particles in the scattered light.
When the light from stars enters the atmosphere, the light with smaller wavelengths gets easily scattered, while lights with longer wavelength do not scatter much and hence travels straight. This gives red colour to the sky during sunrise and sunset. On the other hand, the shorter wavelengths scatter in the sky and give the sky its usual blue colour.

Question :  A person needs a lens of power -5.5 diopters for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 diopter. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

Question : The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Answer : For the myopic eye

Question : What is the cause of dispersion?
Answer : All colours of light travel at the same speed in a vacuum. A light ray is refracted (bent) when it passes from one medium to another at an angle and its speed changes. At the interface, it is bent in one direction if the material it enters is denser (when light slows down) and in the other direction if the material is less dense (when light speeds up).
Because different wavelengths (colors) of light travel through a medium at different speeds, the amount of bending is different for different wavelengths. Violet is bent the most and red the least because violet light has a shorter wavelength, and short wavelengths travel more slowly through a medium than longer ones do. Because white light is made up of all visible wavelengths, its colors are be separated (dispersed) by this difference in behavior.

Question :  A person is unable to read a book properly. From which defect is he suffering? How to correct this defect?
Answer :  The person is suffering from hypermetropia or long-sightedness.
A long sighted person can see distant objects clearly, but cannot see distinctly objects lying closer than a certain distance. Thus, he cannot see clearly an object lying at 25 cm which is the least distance of distinct vision for a normal eye. His far point is
farther from the eye than 25 cm, say at 75 cm or so.
Causes of the defect: This defect is due to either :
Normal eye : It is able to focus the rays from normal near point (25 cm from eyes)

Defective eye: Due to eye ball getting short or an increase in focal length of eye lens, the rays do not focus on retina.
Defective eye: is able to form image at retina when object is moved from N to N' the near point of defective eye.

Corrected eye : A convex (or any convergent) lens of suitable focal length converges the rays to match those coming from N'. Hypermetropic eye.
Normal eye is able to focus on retina the rays emerging out from N.
However, the defective eye is not able to focus the rays from near point of normal eye i.e. N.
It can focus the rays from near point of defective eye. i.e. N'.
From fig. we conclude that more inclined rays are not focused on retina whereas less inclined rays from N' get focused on retina.
Correction of this Defect: Such a defect is corrected by placing a convex or converging lens of suitable focal length before the eye so that the rays diverging from N appear to come, after refraction, from the near point N'.
i. the size of the eye ball becoming too short.
ii. the lens becoming too thin, so that its focal length becomes abnormally large.

Question :  Make a diagram to show how hypermetropia is corrected. The near point of hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of normal eye is 25 cm.
Answer :   For diagram of correction of hypermetropia,

Numerical

Question : With the help of well labeled diagram, explain the construction and working of human eye.
Answer :   Human eye is the most remarkable and most delicate optical instrument.
Though in principle, it is similar to a photographic camera, it is far most delicate and perfect than the finest camera ever designed by human ingenuity.
Structure : The human eye consists of nearly spherical ball of about 2.5 cm diameter.
Its outermost coating is made of a tough and opaque white substance known as SCLEROTIC. Sclerotic preserve the shape of eye and protects it against external injury.
Front portion of sclerotic is transparent and slightly bulged outwards and known as CORNEA.
There is a layer of black tissues, below sclerotic and is called CHOROID. It serves to absorb any stray light and thus avoids blurring of the image by reflection from the eye-ball.
In font of eye, choroids merge into a coloured diaphragm known as iris which a hole in the middle called PUPIL. When we refer to the colour of eyes of a person, we refer to the colour of iris of the person. This iris corresponds to the stop in the camera. By means of involuntary muscle control, it regulates the amount of light entering the eye.
In strong light, the pupil contracts so as to admit less light whereas in dim light, it expands so as to admit as much light as required.
Behind iris is a crystalline lens with jelly-like layers. The lens is held in position with the help of ciliary muscles. The lens divides the eye ball into two chambers – the front chamber called anterior chamber and other between lens and the retina called posterior chamber. Anterior chamber is filled with a fluid called aqueous humour while the posterior chamber is filled with a jelly like substance called vitreous humour.
The innermost coating of the eye, covering the rear of inner surface, is a very delicate membrane called the retina. It is richly supplied with blood vessels and nerve fibres and serves as a light-sensitive screen to receive the image. The sensation of vision in the retina is carried to the brain by a nerve called optic nerve. The most sensitive part of retina is known as the yellow spot. It is a slightly raised portion with a slight depression known as the fovea centralis. The point where the optic nerve enters the eye is totally insensitive to light and is known as the blind spot.
Eye Lids are provided to control the amount of light falling on the eye. Lids also protect the eyes from dust etc.
How does the eye focus: In eye, the distance between lens and the retina remains the same, while crystalline lens automatically changes its focal length by changing its curvature due to pull or push of ciliary muscles according to the distance of the object so as to bring the image to a sharp focus upon the retina. While seeing the far objects such as distant tree, the eye lens becomes thinner and flatter so as to increase its focal length. To see the objects close to the eyes, such as printed page, the lens becomes thicker so as to decrease its focal length. The process by which the eye can adapt itself to see objects at different distances is called accommodation.
Range of vision : The most distant point upto which a fully relaxed eye can see is called the far point. For normal eye, far point is infinity. The point at the shortest distance from the eye upto which the eye can accommodate itself and therefore, can see clearly is known as the near point. It is about 15 cm for a normal eye. The distance between far and near points is called range of vision or accommodation. Within the range of vision, there is a certain distance where the object is most clearly seen. The distance for a normal eye is about 25 cm and is known as the least distance of distinct vision.
Persistence of vision: Time for which the impression of the object seen by the eye remains on the retina even after the removal of the object is called the persistence of vision.

Question : What is meant by power of accommodation of the eye?

Question : Define the following terms- a)Persistence of vision b) Far point of the eye c)Near point of the eye  d)Least distance of distinct vision

Question : What is the condition of the ciliary muscles of the eye when the eye is looking at a distant object. What is its effect on the focal length of the eye lens?

Question : Why are we not able to see things clearly for some time when we enter fro bright light to a darkened cinema hall?

Question : A student has difficulty in reading the blackboard while sitting on the last desk. From what defect of vision is he suffering? How can it be corrected? Draw ray diagram for it.

Question : What happens to the image distance in the eye when we increase the distance of an object from the eye?

Question : What do you mean by dispersion?

Question : Why do different colours deviate through different angles on passing through a prism?

Question : How do we see colours?

Question : Why does the sky appear dark instead of blue to an astronaut?

Question : Why does the sun appear reddish early in the morning?

Question : Explain the formation of a rainbow.

Question : What is the cause of twinkling of stars?

Question : Why are danger signal lights red in colour?

Question : What information do we get about sunlight from the formation of a rainbow?

Question : Why does the sun appear red at sunrise and sunset?

Question : What are ‘bifocal’ lenses?Under what condition(s) are these required by a person?

Question : A person with a myopic eye cannot see objects beyond 1.2m distinctly. What should be the nature of corrective lens to restore proper vision? (P= -0.83 Lens – concave)

Question : The near point of a hypermetropic eye is at 75 cm from the eye. What is the power of the lens required to enable him to read clearly a book held at 25 cm from the eye? (P= 2.66D)

Question : A myopic person uses specs of power – 0.5D. What is the distance of far point of his eye? (2m)

Question : A person wants to read a book placed at 20 cm, whereas near point of his eye is 30 cm. calculate the power of the lens required (1.67D).

Question : The far point distance of a short sighted person is 1.5meters. find the focal length, power and nature of the remedial lens? (-1.5 m, -0.67D, concave lens)

Question : A person having a myopic eye uses a concave lens of focal length 10 cm. Find the power of the lens. (-10D)

Question : A person with myopic eyes is nit able to see objects beyond 3 m. determine the nature, focal length and power of the correcting lens? (divergent, -3m,-3.3D)

Question : A person can see clearly up to 3m. Name the defect of vision he is suffering from. What type of lens should be used so that he can clearly see up to 12m.find its power. (-0.25D)

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