CBSE Class 10 Physics The Human Eye and The Colorful World Worksheet Set D

Question. The sky appears dark to passengers flying at very high altitudes mainly because :
(a) Scattering of light is not enough at such heights.
(b) There is no atmosphere at great heights.
(c) The size of molecules is smaller than the wavelength of visible light.
(d) The light gets scattered towards the earth.
Answer : (a) Scattering

Question. If a person can see a doll at the far distance, but he cannot have the newspaper in his hands. What lens should he wear to make correct his eyesight ?
(a) Convex lens
(b) Concave lens
(c) Bi- focal lens
(d) Prism
Answer : (b) Concave lens

Question. The image formed by the retina of the human eye is :
(a) Virtual and erect
(b) Real and inverted
(c) Virtual and inverted
(d) Real and erect
Answer : (b) Real and inverted

Question. The persistence of vision for the human eye is :
(a) 1/10 thof a second
(b) 1/16th of a second
(c) 1/6 thof a second
(d) 1/18 th of a second
Answer : (b)

Question. The light-sensitive cell present on the retina and is sensitive to the intensity of light is :
(a) Cones
(b) Rods
(c) Both rods and cones
(d) None of these
Answer : (b) Rods

Question. The phenomena of light responsible for the working of the human eye is :
(a) Reflection
(b) Refraction
(c) Power of accommodation
(d) Persistence of vision
Answer : (b) Refraction

Question. Match the following
Column I                                      Column II
(a) Carries signals from an           (i) Ciliary muscles
eye to the brain
(b) Muscle which change              (ii) Eye-lens
snaps of eye-lens
(c) A clear window at font              (iii) Optic nerve
(d) Change shape to focus a        (iv) Cornea
picture on retina.
Answer : (a) (iii), (b) (i), (c) (iv), (d) (ii).

Question. Fill in the blanks

(a) A short-sighted person cannot see ............ objects clearly.
(b) When a ray of light enters a prism, it bends .............. the normal.
(c) The blue colour of sky is due to ............... of light.
Answer :
(a) distant, (b) towards, (c) scattering.

Very Short Answers Type Questions

Question. Where do we see (a) concave and (b) convex lens in bifocal lenses ?
Answer :
(a) Concave lens—Upper part
(b) Convex lens—Lower part.

Question. Name the principle on which a prism form the image of an object ?
Answer : Refraction of light.

Question. What do you mean by a rainbow ?
Answer : Rainbow is a natural spectrum formed in the sky after rain shower due to dispersion of light caused by suspended water droplets in atmosphere.

Question. Give an example in nature which shows that sunlight may be made up of different colours.
Answer : Formation of rainbow.

Question. What is persistence of vision ?
Answer : The image of any object formed on the retina persists for about 1/16 of a second. This continuance of sensation of eye for sometime even after the removal of the object is called persistence of vision.

Question. What do you mean by far point of human eye ?
Answer : The most distant point at which an object can be seen clearly by the eye is called the far point of the eye.

Question. In the formation of spectrum of white light by a prism which colour is :
(a) deviated least ? (b) deviated most ?
Answer : (a) Red, (b) Violet.

Short Answer Questions

Question. Define the term power of accomodation. Write the modification in the curvature of the eye lens which enables us to see the nearby objects clearly ?
Answer : The ability of the eye lens to adjust its focal length, is called the power of accommodation. There should be a contraction of ciliary muscles, that will increase the curvature of the eye lens and becomes thicker, so the focal length of the eye lens will decrease. It will thus enable us to see the objects clearly.

Question. Write the structure of eye lens and state the role of ciliary muscles in the human eye. 
Answer : The eye lens of the human eye is a convex lens that is thick in the middle and thin from the edges. It converges the incident light rays and forms the image on retina.
Role of ciliary muscles :
(a) It changes the shape of the lens in eye to help with focussing.
(b) It helps to regulate the flow of aqueous humor in eye.

Question. What happens to the image distance in the normal human eye when we decrease the distance of an object, say 10 m to 1 m ? Justify your answer.
Answer : The image distance will remain unaffected even if we change the object distance because the image is formed on the retina.

Question. A person is advised to wear spectacles with (a) Convex lenses, (b) Concave lenses. What type of defect of vision is he suffering from ?
Answer :
(a) Hypermetropia or long-sightedness.
(b) Myopia or short-sightedness.

Question. What is scattering of light ? Why is the colour of the clear sky blue ? Explain.
Answer :
(a) The phenomenon in which a part of the light incident on a particle is redirected in different directions.
(b) When sunlight passes through the atmosphere, its fine particles scatter the blue colour more strongly than red. So, the scattered blue light enters our eyes.
Hence the sky appears blue.

Question. What is atmospheric refraction ? List two phenomena which can be explained on the basis of atmospheric refraction.
Answer : In atmosphere, there are layers of different densities and refractive indices, when light ray is passed through these layers refraction of light takes place which is
called atmospheric refraction.
Two phenomenon that can be explained on the basis of atmospheric refraction are :
(a) Twinkling of stars.
(b) Early sunset and delayed sunrise.

Question. What is presbyopia? How can it be corrected?
Answer : Presbyopia is caused due to decrease in the power of accommodation of the eyes due to ageing and weakening of ciliary muscles diminishing flexibility of eye lens. A person with this defect cannot see nearby as well as far off objects clearly.
Correction: It can be corrected by using bi-focal lens with both concave and convex lens in it.

Question. The near point of hypermetropic eye is 80 cm. What is the nature and power of the lens required to enable him to read a book placed at 25 cm from the eyes?
Answer : Near point = 80 cm
Object distance u = – 25 cm
ν= – 80 cm (convex lens in case of hypermetropia)
1/f = 1/v − 1/u
 = 1/( -80) −  1/( −25)
∴
1/f  =  -1/( 80) + 1/25
= −5 + 16/400
1/f = +11 /400
+
∴ f = 400/11 = 36.36 cm
f = 0.36 m
Power of lens P = 1/f = 1/0.36 = 2.7 D

Question. A student can see objects clearly only when the objects are lying at distances between 60 cm and 320 cm from the eye.
(a) What kind of eye defect he is suffering from?
(b) What kind of lens will be required to increase his range from 25 cm to infinity?
Explain briefly.
Answer : Student is suffering from myopia. It can be corrected by using concave lens of appropriate focal length and power. The light rays meet before retina and hence concave lens will help the rays to diverge further and help them in meeting on retina.

 

Question. Near point of a hypermetropic eye is at 1 m. Find the focal length, power and nature of lens used to correct this defect.
Answer : Near point of hypermetropic eye is 1 m i.e., 100 cm. The eye cannot see objects between 100 cm and 25 cm.
u = – 25 cm
ν = – 1 m = – 100 cm
∴
1/f = 1/v − 1/u
= −1/100 − 1/(−25)
= − 1/100 + 1/25
1 /f = -1+4/100 = 3/100

f = 100/3 cm = 1/3
P = 1/f = ¹/_1/3
∴ P = + 3 Dioptre
Convex lens of power 3D is used to correct this defect.

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.

HOTS Question

Question. How does the size of particles present in medium produce different colours of light by its scattering property?
Answer : The colour of the scattering light in a medium depends on the size of the scattering particles.
(i) If the size of particles is very small, it will scatter mainly blue light.
(ii) If the size of particles is larger then it will scatter light of longer wavelength i.e., red.
(iii) If the size of scattering particles is larger enough, the light appears to be white.

Question. To correct myopia why we use concave lens and to correct hypermetropia, why do we use convex lens? Why can’t we do vice-versa?
Answer : Myopia is a defect in which the image is formed in front of retina. We need to use diverging lens so that it can further diverge the light rays before it enters our eye and make it possible to meet on the retina.
In case of hypermetropia, the image is formed beyond retina, we need to use convex lens so as to converge the rays and make it possible for the rays to meets on the retina.

Question. Why does light splits into spectrum when it passes through prism only and does not split when it passes through glass slab?
Answer : Rectangular glass slab has parallel refracting surfaces, the emergent ray is parallel to the incident ray. It slightly gets displaced laterally. While in case of prism the surface is not parallel and the light ray gets deviated at larger angle due to which it splits into its constituent colour.

VBQs Question

Question. Rohan’s father is an eye surgeon. He persuaded his father to put a camp in his society for educating people on eye-donation. Rohan made a banner. One donation can give eye-vision to two blind persons.
(a) Name the part of the eye that is used during eye transplant.
(b) Name the defect that can be corrected by this transplant.
(c) What value of Rohan is reflected?
Answer : (a) Cornea is used for eye transplant.
(b) Defects caused due to cornea can be corrected by eye donation.
(c) Rohan shows sympathy, compassion and empathy in his behaviour.

Assertion and Reason Type MCQs :

Following questions consists of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
A. Both assertion and reason are true, and reason is the correct explanation of assertion.
B. Both assertion and reason are true, but reason is not the correct explanation of assertion.
C. Assertion is true but reason is false.
D. Assertion is false and reason is true.

Question. Assertion(A): The stars twinkle, while the planets do not.
Reason (R): The stars are much bigger in size than the planets.

Answer: B

Question. Assertion (A): The twinkling of stars is due to the fact that refractive index of the earth’s atmosphere fluctuates.
Reason (R): In cold countries, the phenomenon of looming (i.e ship appears in the sky) takes place, because refractive index of air decreases with height.

Answer: B

Question. Assertion(A): Sun looks reddish at sunrise and sunset.
Reason (R) : Sun rays have to pass through smaller distance in atmosphere.

Answer: C

Question. Assertion: The colour of the scattered light does not depend on the size of the scattering particles.
Reason: Red light is used as a danger signal because it can travel longer distances through rain and fog.

Answer: C

Question. Assertion(A): The red light bends the least while the violet bends the most.
Reason(R): Red light has short wavelength whereas violet has long wavelength.

Answer: C

Question. Assertion: The path of light is visible due to scattering of light.
Reason : Tiny water droplets in the mist scatter light.

Answer: B

Question. Assertion (A) : At Mid-day sun appears to be bright white .
Reason (R) : Scattering occurs due to size of dust particles and Air molecules.

Answer: A

Question. Assertion(A): A prism can split the incident white light into bands of different colours.
Reason(R): The different colours of light bend through different angles with respect to the incident rays.

Answer: A

I. The phenomenon of splitting of white light into its seven constituent colors when it passes through a glass prism is called dispersion of white light. The various colors seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red. The sequence of colors remembers as VIBGYOR. The band of seven colors is called the spectrum. 

Question. The angle between incident ray and emergent ray of a prism is called .
A. Angle of Refraction
B.Angle of deviation
C.Angle of incidence
D.Angle of emergence

Answer: B

Question. What happens when white light is passed from air to glass prism ?
A. Reflects back
B. Bends away from normal
C. Un deviated
D. Bends towards normal

Answer: D

Question. Which Color deviates most in the formation of spectrum of white light by a prism ?
A. VIOLET
B. ORANGE
C. GREEN
D. RED

Answer: A

II. A collection of suspended water droplets in the atmosphere serves as a refractor of light. The water represents a medium with a different optical density than the surrounding air. Light waves refract when they cross over the boundary from one medium to another. The decrease in speed upon entry of light into a water droplet causes a bending of the path of light towards the normal. And upon exiting the droplet, light speeds up and bends away from the normal. 

The droplet causes a deviation in the path of light as it enters and exits the drop.
There are countless paths by which light rays from the sun can pass through a drop. Each path is characterized by this bending towards and away from the normal.
One path of great significance in the discussion of rainbows is the path in which light refracts into the droplet, internally reflects, and then refracts out of the droplet. The diagram at the right depicts such a path. A light ray from the sun enters the droplet with a slight downward trajectory. Upon refracting twice and reflecting once, the light ray is dispersed and bent downward towards an observer on earth's surface. Other entry locations into the droplet may result in similar paths or even in light continuing through the droplet and out the opposite side without significant internal reflection. But for the entry location shown in the diagram at the right, there is an optimal concentration of light exiting the airborne droplet at an angle towards the ground. As in the case of the refraction of light through prisms with nonparallel sides, the refraction of light at two boundaries of the droplet results in the dispersion of light into a spectrum of colors. The shorter wavelength blue and violet light refract a slightly greater amount than the longer wavelength red light. Since the boundaries are not parallel to each other, the double refraction results in a distinct separation of the sunlight into its component colors.

Question. When compared to air, medium of water droplet is
A. Optically rarer
B. Has same optical density
C. Optically insignificant when compared to air
D. Optically denser.

Answer: D

Question. Rainbow can also be observed on a sunny day when an observer looks at the sky through a waterfall or a sprinkler source or through a water fountain with the following condition.
A. Sun between the observer and the water source.
B. Sun behind the observer.
C. Sun behind the water source with observer in the opposite direction.
D. Position of sun does not affect the formation of rainbow.

Answer: B

Question. The speed of light from sun when enters the water droplet undergoes this phenomenon
A. its speed decreases
B. Light gets absorbed in the droplet
C. it becomes monochromatic
D. Passes through undeviated

Answer: A

Question. The rainbow formation could be because of the following reasons
A. light being reflected when entering a droplet of water, then refracted inside on the back of the droplet and refracted again when leaving it.
B. light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it.
C. . Due to interference of different wavelengths in white light
D. All scenarios possible.

Answer: B

III.  Atmospheric refraction is the phenomenon of bending of light on passing through earth’s atmosphere. As we move above the surface of earth, density of air goes on decreasing. Local conditions like temperature etc. also affect the optical density of earth’s atmosphere. On account of atmospheric refraction, stars seen appear higher than they actual are; advanced sunrise; delayed sunset, oval appearance of the sun at sunrise and sunset; stars twinkle, planets do not.

Question. The sun appears oval shaped or flattened due to
A. dispersion
B. scattering
C. atmospheric refraction
D. cannot say

Answer: C

Question. Twinkling of stars and non-twinkling of planets is accounted for by
A. scattering of light
B. dispersion of light
C. atmospheric refraction
D. none of these

Answer: C

Question. In absence of atmosphere, the colour of sky appears
A. blue
B. black
C. red
D. yellow

Answer: B

Question. Due to atmospheric refraction, apparent length of the day
A. increases
B. decreases
C. remains the same
D. all of these

Answer: A

Question. Apparent position of the star appears raised due to
A. atmospheric refraction
B. scattering of light
C. both (a) and (b)
D. none of these

Answer: A

SECTION A

• CONCEPTUAL QUESTIONS

1 Imagine for a moment that the earth has no atmosphere. What would be the colour of sky in such case? Give reason for your answer.

2 Newton placed two triangular prisms in inverted position with respect to each other. He is then let white light pass through them. What was his observation on screen? Draw diagram of this experiment.

3 The power of a lens is +1.5D. Name the type of defect of vision that can be corrected using this lens. Draw a ray diagram to illustrate this defect of vision.

4 What is meant by least distance of distinct vision? Mention its value. 

5 Explain how is the focal length of eye lens is changed by the ciliary muscles when object distance when object distance from it changes?

6 Explain the formation of rainbow in the sky with the help of diagram. State the phenomena involved in proper sequence.

7 A person is unable to see the objects beyond 2m clearly. Name the defect of vision he is suffering from. State two causes due to which this defect may arise. Draw ray diagrams to show the defect of vision and correction of this defect using an appropriate lens.

8 Why is normal eye not able to see clearly the objects placed closer than 25cm?

9 What is atmospheric refraction? What is its cause?

10 How is the amount of light entering the eye controlled?

11 The time difference between actual sun set and the apparent sun set is 2 minutes. Explain this fact with the help of diagram

12 How does the size of particles affect the scattering of light? 

13 Red lights are used as warning signals at road crossing. Why? 

14 Name the following parts of human eye:

(i) A thin membrane through which light enters

(ii) The part of eye sensitive to light.

15 List the factors on which the angle of deviation through a prism depends. 

16 Why do stars twinkle but not the planets?

17 “Stars seem higher than they actually are” – explain why?

18 Draw a neat diagram to show refraction of light ray through a prism. Mark angle of incidence, angle of emergence and angle of deviation.

19 Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of the defect. Name the type of lens required such persons

20 Write the function of each of the following parts of the Human eye. i) Cornea ii) Iris iii) Crystalline lens iv) Ciliary muscles v) Retina

21 I) What is Tyndall effect?

ii) Draw a figure which shows the arrangement for observing the phenomenon of scattering of light in laboratory?

iii) What colours would you observe in the experiment? Why?

Section B

• Numerical problems

22 A person with a myopic eye cannot see beyond 1.2m distinctly. What should be the power of corrective lens used to restore his proper vision?

23 The near point of Hypermetropic eye is 75cm from the eye. What is the power of the lens required to enable him to read clearly a book held at 25cm from the eye?

24 The near point of Hypermetropic eye is 100cm from the eye. What is the power of the lens which he requires to read clearly a book held at 25cm from the eye?

25 The far point of a person is 2m. Find the power and focal length of the lens required to rectify this problem.
 

Please click on below link to download CBSE Class 10 Physics The Human Eye and The Colorful World Worksheet Set D