Please refer to Chapter 11 Human Eyes and Colourful World Class 10 Science Important Questions with solutions provided below. These questions and answers have been provided for Class 10 Science based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 10 Science for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 10.
Class 10 Science Important Questions Human Eyes and Colourful World Chapter 11
Very Short Answer
Question. Which part of the eye controls the amount of light entering the eye?
Answer : Pupil controls the amount of light entering the eye.
Question. How can change of size of eyeball be one of the reason for: (a) Myopic (b) Hypermetropic Compare the size of eyeball with that of a normal eye in each case. How does this change of size affect the position of image in each case?
Answer : (a) The eye suffering from myopia, has long eye ball than that of normal eye due to which the retina is at a larger distance from the eye lens. This results in the formation of the image in front of the retina.
(b) The eye suffering from hypermetropia has short eye ball than that of normal eye due to which the retina is smaller distance from the eye lens. This results in the formation of the image behind the retina.
Question. What is eye lens made of ?
Answer : Eye lens is made of transparent and flexible jelly like material.
Question. Name the two phenomena involved in the formation of rainbow.
Answer : The phenomena involved in formation of rainbow are dispersion and total internal reflection and refraction.
Question. Name the component of white light that deviates the least and the most while passing through a prism.
Answer : Red colour deviates the least and violet colour deviates the most.
Question. A person is advised to wear spectacles with concave lenses. What type of defect of the vision is he suffering from?
Answer : Myopia.
Question. How is the sense of vision carried from the eye to the brain?
Answer : Through optical nerve, sense of vision is carried from eye to the brain.
Question. Which liquid fills the space between eye lens and retina?
Answer : Vitreous humour.
Question. Why is blind spot so called?
Answer : An image formed at this point is not sent to brain.
Question. A person suffering from an eye defect uses lenses of power – 1D. Name the defect he is suffering from and the nature of lens used.
Answer : He uses a concave lens (negative power) because he is suffering from myopia.
Question. Which colour of white light suffers (i) least deviation and (ii) maximum deviation when a beam of white light passes through a glass prism?
Answer : Longer wavelength light (red) suffers least deviation and shorter wavelength (violet) suffers maximum deviation when white light is passed through a prism. depends. Why does the sky appear dark in space?
Answer : Scattering of light depends on the presence of atmosphere which contains water droplets, molecules of air, smoke and dust particles.
In the space, there is no atmosphere to scatter light.
Question. What is the number of receptors contained in the retina?
Answer : Retina contains more than 125 millions receptors which are of two types, rods and cones.
Question. What is meant by far point?
Answer : The farthest point upto which an normal human eye can see objects clearly is known as far point.
Question. Why can you not see an object clearly if it is placed very close to your eye?
Answer : For a human eye, there is a near point, 25 cm. If the distance of the object is lesser than this distance, eye cannot see object clearly.
Question. What is Presbyopia ?
Answer : Presbyopia is a kind of eye defect in old persons due to ageing. It happens due to decrease in flexibility of eye lens and weakening of ciliary muscles.
Question. What is twinkling of stars due to?
Answer : Twinkling of star is due to atmosphere refraction.
Question. Define dispersion of white light.
Answer : The splitting of white light into its constituents seven colours is called dispersion of light.
Question. What kind of lens is used in the spectacles of a person suffering from myopia (near sightedness)?
Answer : A diverging lens/concave lens is used for a person suffering from near sightedness/ myopia.
Question. Name the part of the human eye that helps in changing the focal length of the eye lens.
Answer : Ciliary muscles help in changing the focal length of the eye lens.
Question. Write the value of near point of distinct vision for normal eye.
Answer : For a normal human eye the value of near point of distinct vision is 25 cm.
Question. What is the role of pupil in a human eye?
Answer : Pupil regulates and controls the amount of light entering in the eyes.
Question. What is the range of vision for a normal human eye?
Answer : Range of vision is 25 cm to infinity.
Question. Name the part responsible for the power of accommodation of the eye.
Answer : Ciliary muscles help for the power accommodation of the eye.
Question. Name the essential parts of human eye,
Answer : (a) Retina (6) Eye lens (c) Cornea (d) Pupil (e) Iris
Question. Which liquid fills the space behind the cornea?
Answer : Aqueous humour is filled in the space behind the cornea.
Question. Name the condition resulting due to the eye lens becoming cloudy.
Answer : Cataract.
Question. When you enter from a bright sunshine into a dark room, you are not able to see clearly for sometime, why?
Answer : In bright light, pupil had become small.
Question. On what factor the colour of the scattered light depends?
Answer : The colour of the scattered light depends on the size of scattered particles.
Question. Why sky appears dark to the passengers flying at high altitudes?
Answer : There is no atmosphere at high altitudes. Hence no scattered light can reach to the eye.
Question: What will be the observed colour of sky on a planet where there is no atmosphere? Why?
Answer: Observed colour of the sky on a planet where there is no atmosphere will be black because there is no air molecules to scatter the light coming from the sun.
Question: Why does sky look blue on a clear day?
Answer:The colour of clear sky is blue due to the scattering of light having shorter wavelength by the air molecules present in the atmosphere
Question: Why does the Sun appear reddish at sunrise?
Answer: The Sun appears reddish at sunrise is due to scattering of light by the particles present in the atmosphere.
Short Answer I
Question: Draw a labelled diagram to explain the formation of a rainbow in the sky.
Answer: A rainbow is a natural spectrum caused by dispersion of sunlight by tiny water droplets, present in the atmosphere.
Short Answer: II
Question: State the function of each of the following parts of human eye:(i) Cornea (ii) Iris (iii) Pupil
Answer: (i) Cornea : It is a transparent bulge on the fron surface of eyeball which refracts most of the light rays entering the eye.
(ii) Iris is a dark muscular diaphragm that controls the size of the pupil..
(iii) Pupil : It controls the amount of light entering into the eye.
Question: What is hypermetropia? State the two causes of hypermetropia. With the help of ray diagrams, show:
(i) the eye-defect hypermetropia
(ii) correction of hypermetropia by using a lens
Answer: Hypermetropia : It is a defect in an eye in which a person is not able to see nearby object distinctly but can see far objects clearly.
Hypermetropia is caused due to following reasons:
(a) Shortening of the eyeball
(b) Focal length of crystalline lens is too long.
Question: Write about power of accommodation of human eye. Explain why the image distance in the eye does not change when we change the distance of an object from the eye?
Answer: The ability of the eye lens to adjust its focal length is called power of accommodation. The ciliary muscles modifies the curvature to some extent. The change in the curvature of the eye lens can thus change its focal length. Thus, the focal length of the human lens increases or decreases depending on the distance of the object value to this distance of the image does not change. For example, when the ciliary muscles are relaxed, the lens becomes thin and its focal length increases, thus enables us to see distant object clearly.
Question: What eye defect is myopia? Describe with a neat diagram how this defect of vision can be corrected by using a suitable lens.
Answer: Myopia is also known as near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.
Myopia can be corrected by using concave lens of appropriate focal length.
Question: Name the three common defects of vision. What are their causes? Name the type of lens used to correct each of them.
Answer: Three common defects of vision are
(i) Myopia
(ii) Hypermetropia
(iii) Presbyopia
Myopia can be caused due to following reasons.
(a) Elongation of eyeball.
(b) Excessive curvature of eye lens.
Hypermetropia can be caused due to following reasons.
(a) Shortening of eyeball.
(b) Focal length of eye lens becomes too long.
Presbyopia is caused due to gradual weakening of ciliary muscles and diminishing flexibillity of eye lens due to ageing.
Correction of these defects:
(i) Myopia can be corrected by using concave lens of appropriate focal length.
(ii) Hypermetropia can be corrected by using convex lens of appropriate focal length.
(iii) Presbyopia can be corrected by using bifocal lens.
Question: (a) Draw a diagram to show the formation of image of a distant object by a myopic eye. How can such an eye defect be remedied?
(b) State two reasons due to which this eye defect may be caused.
(c) A person with a myopic eye cannot see objects beyond a distance of 1.5 m. What would be the power of the corrective lens used to restore proper vision?
Answer:
This defect can be correct by using concave lens.
(b) Myopia can be caused due to the following reasons.
(i) Excessive curvature of the eye lens
(ii) Elongation of the eyeball
(c) The far point of this myopic person is 1.5 m (This means a person can see a distant object kept at inffnity clearly if the image of the
object is formed at his in nity i.e., at 1.5 m)
Question: About 3.5 crore people in the developingworld are corneal blind. About 30 lac blindchildren below the age of 12 can be curedby replacing the defective cornea with the cornea of a donated eye. What can a student of your age do in order to create awareness about this fact among people of your locality and why?
Answer: To create awareness among the people, we as a student can do the following.
(i) Organise a team of 3-4 members for eyedonation champion.
(ii) We can organise a play to aware people about the importance of donating an eye.
(iii) We can demonstrate poster and banner and take a walk around the area. We must spread such awareness to encourage people to donate their eyes after their death so that the children below 12 years have to see this world as they are the future of our country.
Question: (a) What is Presbyopia? State the cause of presbyopia. How is Presbyopia of a person corrected?
(b) What is meant by power of accommodation of the eye of a person?
Answer: (a) : Presbyopia is a defect in eye where anold person is not able to see the nearby object distinctly.
Cause : Presbyopia is caused by the gradual weakening of ciliary muscles and diminishing flexibillity of eye lens.
Correction : Presbyopia can be corrected by using appropriate convex lens or bifocal lens if he suffers from both myopia or hypermetropia.
(b) Power of accommodation of the of a person is the ability of crystalline lens to adjust its focal length
Question: What is ‘dispersion of white light’? State its cause. Draw a ray diagram to show the dispersion of white light by a glass prism.
Answer: Splitting of white light into its seven constituent colours due to refraction is known as dispersion of white light.
Cause of dispersion : When a beam of white light enters a prism, it gets refracted and splits into seven constituent colours. The splitting of the light ray occurs due to the different bending angle for each colour. Thus, each colour ray when passing through the prism bends at different angles with respect to the incident beam, thus gives rise to a spectrum.
Question: What is a spectrum? How can we recombine the components of white light after a glass prism has separated them? Illustrate it by drawing a diagram.
Answer: Spectrum : The band of the colored components of a light beam is called its spectrum.
We recombine the components of white light by placing a second identical prism in an inverted position with respect to first prism.
On passing white light to the first prism it splits into colours of the spectrum. Then this spectrum is allowed to pass through a second identical prism in an inverted position with respect to the first prism. Then, we found a beam of white light.
Long Answer:
Question: (a) List the parts of the human eye that control the amount of light entering into it. Explain how they perform this function?
Answer: (a) The part of the human eye that control the amount of light entering into it is pupil. Light enters the eye through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea, the crystalline lens merely provides the linear adjustment of focal length required to focus objects at different distances on the retina. Iris which is behind the cornea controls the size of the pupil. The pupil regulates and controls the amount of light entering
the eye.
Question: Millions of people of the developing countries of world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission how would you contribute in this noble cause?
(i) State the objective of organising such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
Answer: (i) The objective of organising such campaign is to make people aware and realize their duties towards society.
(ii) (a) By donating our eyes after the die, we can light the life of a blind person.
(b) One pair of eyes gives vision to two corneal Blind people.
(iii) (a) It shows the concern for others.
(b) It also shows the responsible behavior towards the society.
Question: Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due do gradual weakening of the ciliary muscles in old age. What type of lenses are required by the persons suffering from this defect to see the objects clearly?
Akshay, sitting in the last row in his class, could not see clearly the words written on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.
In the context of the above event, answer the following questions:
(a) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?
(b) State the values displayed by the teacher and Salman.
(c) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?
Answer: Ciliary muscles modifies the curvature of eye lens and hence adjusts its focal length. This enables us to see objects.
The defect of vision is presbyopia, person suffering from this defect should wear bifocal lenses. These lenses consists of both concave and convex lenses.
(a) Akshay is suffering from myopia or nearsightedness. He should use concave lens to correct this defect.
(b) Teacher and salman are concerned and caring.
(c) Akshay can show his gratitude by saying thank you.
Question: A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. (a) 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, end the power of the lens as per the new Cartesian sign convention.
Answer: (a) The two possible reasons due to which the defect of vision arises are : excessive curvature of the eye lens elongation of the eye ball.
(i) A student with myopia has the far point nearer than infinity, thus, the image of a distant object is formed in front of the retina. In the given case the student is not able to see distinctly the objects placed beyond 5 m from his eyes are formed in front of the retina hence, it appears blurred.
(ii) This defect can be corrected by using a concave lens of suitable power as it brings the image back on to the retina, thus the defect is corrected.
(b) focal length, f = 5 m
P=-1/f(inmeters) or, p=1/5=-0.2D
Hence, the power is – 0.2 D.
Question. A person needs a lens of power –0.5 dioptre for correcting his distant vision he needs a lens of power +1.5 dioptre for correcting his near vision. What is the focal length of the lens required for correcting his
(i) distant vision, (ii) near vision?
Answer : i. For correcting his distant vision.
P =- 0.5D
f = 1/P = 1/-0.5 = -2.0
ii. For correcting his near vision
f = 1/P = 1/+1.5 = + 0.67m
Question. (a) Explain why colour of clear sky appears blue during the day with the help of diagram.
(b) Explain why Sun looks reddish at the time of sunrise and sunset.
Answer :
(a) Due to scattering of blue colours by the dust particles present in the atmosphere.
(b) During the Sunrise or Sunset, Sun is at the horizon, and sunlight travels a longer distance in the atmosphere. Due to this all colours get scattered except red which reaches to the eye of the observer to whom sun appears reddish in the morning or evening.
Question. A person cannot see the objects distinctly, when placed beyond 2 m.
a. Identify the eye defect.
b. Give two reasons for this defect.
c. Calculate the power and nature of the lens he should be using to see the distant objects clearly.
d. Draw the ray diagrams for the defective and the corrected eye.
Answer :
a. Myopia.
b. Elongation of eye ball or excessive curvature of cornea.
c. P=1/f = 1/-2 = 0.5D
He will be advised to used a concave lens of power – 0.5 D.
d.
Question. A person cannot see the objects distinctly, when placed at a distance less than 50 cm.
a. Identify the defect of vision.
b. Give two reasons for this defect.
c. Calculate the power and nature of the lens he should be using to see clearly the object placed at
a distance of 25 cm from his eyes.
d. Draw the ray diagrams for the defective and the corrected eye.
Answer :
a. Hypermetropia.
b. Decrease in power of eye lens or shortening of eye ball.
Question. (a) What is dispersion of white light? What is the cause of such dispersion? Draw a diagram, to show the dispersion of white light by a glass prism.
(b) A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why it is so.
Answer :
(a) Dispersion : When white light is passed through a prism it splits into its constituent colours splitting of white light into its constituent colours is known as dispersion.
Light of all wavelengths in vacuum travel with the same speed but have the different speeds in a medium due to different refractive light of indices for them. As a result different wavelength, deviate at different angle. Red colour deviates least when as violet colour deviates most.
(b) In glass slab also, dispersion takes place at AB surface, but these splitted colours emerge out in the form of a parallel beam which becomes white. A glass slab whose focus are parallel can be considered as comprising two prisms of same refractive angle. The second identical prism can be considered in an inverted position w.r.t. first prism. When a beam of white light passes from one prism it get dispersed, but on passing through the second inverted prism, the spectrum recombine to form a white light.
Question. (a) Explain the following terms used in relation to defects of vision and corrections provided for them:
(i) Myopia
(ii) Astigmatism
(iii) Bifocal lenses
(iv) Far sightedness.
(b) Describe with a ray diagram how a person with myopia can be helped by spectacles.
Answer :
(a) (i) Myopia is a kind of defect in human eye due to which a person can see near by objects clearly but unable to see the distant objects.
Myopia is due to (i) excessive curvature of cornea (ii) elongation of eye ball.
(ii) Astigmatism is a kind of human eye defect in which he cannot see simultaneously horizontal and vertical lines both. This defect arises either when the cornea or the eye lens or both
are not perfectly spherical. It can be corrected by using cylindrical lenses.
(iii) Bifocal lenses with the ageing a person may suffer myopia and hypermetropia. For ncorrection of these defects he is advised to use bifocal lenses whose upper half is concave
and lower part is convex to see distant and reading purposes respectively.
(iv) Far sightedness, a person suffering from this defect can see distant objects but unable to see nearby objects clearly. The image of an objects is formed beyond the retina. Such
defects can be corrected by using a convex lens.
(b) A person with myopic eye may be advice to use a concave lens of suitable power/ focal length.
Question. Draw a neat labelled diagram of the structure of the human eye and mention the functions of any four parts.
Answer :
a. Cornea: A thin membrane which covers the eye ball which allows the light to enter and refracts the light to focus it as the crystalline lens.
b. Eye Lens: It is a convex lens made of transparent and flexible jelly like material. Its curvature is adjusted by ciliary muscles.
c. Iris: It controls and regulates the light entering the eye by changing the size of pupil.
d. Pupil: It is a hole in the middle of the iris through which light enters the eye.
Question. (a) State two main causes of a person developing near sightedness. With the 3 help of a ray diagram, suggest how he can be helped to overcome this disability?
(b) The far point of a myopic person is 150 cm in front of the eye. Calculate the focal length and power of a lens required to enable him to see distant objects clearly.
Answer :
a. Elongation of eye ball, and excessive curvature of cornea. He may be adviced .to use a concave lens of suitable focal–length.
Question. A person with a defective eye-vision is unable to see the objects nearer than 1.5 m. He wants to read books at a distance of 30 cm. Find the nature, focal length and power of the lens he needs in his spectacles.
Answer : Defect is hypermetropia
Question. (a) How does refraction take place in the atmosphere?
Why do stars twinkle but not the planets?
(b) State any two effects of atmospheric refraction on the sun as observed from the earth.
Answer : (a) Due to change in the density of atmospheric layers when light travel through them gets refracted. It is known as atmospheric refraction. Due to this atmospheric refraction intensity of light, coming from a point sized star same times becomes more and sometimes less, which gives the appearance of twinkling of the star.
(b) (i) Sun can be seen two minute prior it rises and two minute before it sets.
(ii) Twinkling of star.
Question. The far point of a myopic person is 80 cm in front of the eyes. What is the nature and power of the lens required to enable him to see very distant objects distinctly?
Answer : Concave lens is used for myopic eye for point x = 80 cm.
For viewing fat distant object, focal length of lens.
Question. Far point of a myopic person is 40 cm. What type of lens, should he wear so as to see the distant objects clearly? Calculate the focal length and the power of the lens he should use.
Answer :
The person should wear a concave lens. For myopic eye u = 3, v =- 40
1/f = 1/v-1/u
1/f = 1/-40 – 1/∞
1/f = -1/40
p = 100/f(cm) = -100/40 = -2.5D
Question. (a) A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
(b) Why do stars twinkle? Explain.
Answer :
(a) He is suffering from myopia.
Causes of myopia:
(i) elongation of eye ball.
(ii) excessive curvature of cornea.
Concave lens of suitable power is used to correct myopia.
(b) Light coming from stars when enter in the Earth’s atmosphere suffers refraction from the atmospheric layers. Since the densities of atmospheric gases changes frequently. Since the stars are point sized and at a far distance so sometimes star appear brighter and sometimes dimmer which gives the impression as the stars twinkling.
Question. The far point of a myopic person is 150 cm in front of the eye. Calculate the focal length and the power of a lens required to enable him to see distant objects clearly.
Answer :
For myopic person
u = 3, v =- 150 cm
f = ?
From lens formula 1/f = 1/v-1/u
1/-160 – 1/∞ = -1/160
p = 100/f(cm) = -100/150 = -0.66D
=- 0.66 D
