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

Short Answer Questions

Question. Why does the sky appears blue during day time, red during sunrise and sunset and black to an astronaut.
Answer : Sky appears blue during day time because the light of sun gets scattered and the most scattered light is blue, so the sky appears blue.
During evening and early morning when the sun is not over head but it is below the horizon, the only light that reaches our eye is red and hence the sky appear to be reddish in colour.
For an astronaut the sky appears to be black because there is no atmosphere that can refract the light.

Question. When we see any object through the hot air over the fire, it appears to be wavy, moving slightly. Explain.
Answer : The objects beyond the hot air appears to be wavy because the medium for light to pass through changes, the light passes from denser to rarer and then again to denser medium thereby causing refraction in the air. Moreover the refractive index of the hot air keeps changing which leads to give the wavy appearance of the object.

Question. (a) Give reasons for the following:
(i) Colour of the clear sky is blue.
(ii) The sun can be seen about two minutes before actual sunrise.
(iii) We cannot see an object clearly if it is placed very close to the eyes.
(b) What is presbyopia? Write two causes of this defect. 
Answer : (a) (i) Clear sky appears blue because the white light of sun when enters the earth’s atmosphere the large number of molecules present in the earth’s atmosphere scatter the light. As blue light scatters the maximum it reaches our eyes.
(ii) The sun is visible to us 2 minutes before the actual sunrise because of atmospheric refraction. When the sun is below the horizon, the light travelling from rarer to denser medium bends and reaches our eyes creating an impression that it is above the horizon.
(iii) A normal human eye has a near point of 25 cm, anything closer to it is not seen clearly.
(b) Presbyopia: This defect is caused due to ageing. The person suffering from this disease cannot see nearby as well as far off objects. It is caused due to weakening of ciliary muscles. The lens is not able to change the focal length. It can be corrected by using bi-focal lens.

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): In case of rainbow, light at the inner surface of the water drop gets internally reflected.
Reason(R): The angle between the refracted ray and normal to the drop surface is greater than the critical angle.

Answer: A

Question. Assertion(A): The angle of incidence and the angle of emergence are equal.
Reason(R): The angle of refraction and the angle of deviation are not equal.

Answer: B

Question. Assertion: Rainbow is an example of the dispersion of sunlight by the water droplets.
Reason: Light of shorter wavelength is scattered much more than light of larger wavelength.

Answer: B

Question. Assertion(A): Rainbow is formed in the sky due to the dispersion of sunlight by water droplets.
Reason(R): Light of shorter wavelength is scattered much more than the light of longer wavelength.

Answer: B

Question. Assertion: Red light travels faster in glass than green light.
Reason: The refractive index of glass is less for green light.

Answer: C

Question. Assertion(A): The light of violet colour deviates the most and the light of red colour the least, while passing through a prism.
Reason(R): For a prism material, refractive index is highest for red light and lowest for the violet light.

Answer: B

Question. Assertion(A) : Just before sunset ,the sun appears to be elliptical. this may happen due to refraction
Reason (R) : Refraction of light rays through atmosphere may cause different magnification in mutually perpendicular directions.

Answer: A

Question. Assertion(A): The Sun appears flattened at sunrise and sunset.
Reason (R): The apparent flattering of the Sun’s disc at sunrise and sunset is due to atmospheric refraction.

Answer: A

Question. Assertion: The sky appears dark in outer space..
Reason : Scattering does not occur in outer space as there is no atmosphere.

Answer: A

CASE BASED MCQs

I. The spreading of light by the air molecules is called scattering of light.The light having least wavelength scatters more.The sun appears red at sunrise and sun set, appearance of blue sky it is due to the scattering of light.The colour of the scattered light depends on the size of particles.The smaller the molecules in the atmosphere scatter smaller wavelengths of light.
The amount of scattering of light depends on the wavelength of light. When light from the sun enters the earth’s atmosphere , it gets scattered by the dust particles and air molecules present in the atmosphere.The path of sunlight entering in the dark room through a fine hole is seen because of scattering of the sunlight by the dust particles present in its path inside the room.

Question. The colour of sky appears blue, it is due to the
A. refraction of light through the atmosphere
B. dispersion of light by air molecules
C. scattering of light by fine dust particles
D. all of these

Answer: C

Question. To an astronaut in a spaceship , the colour of earth appears
A. red
B. blue
C. white
D. black

Answer: D

Question. At the time of sunrise and sunset , the light from sun has to travel
A. longest distance of atmosphere
B.shortest distance of atmosphere
C. both (A) and (B)
D. can’t say.

Answer: A

II. The spreading of light by the air molecules is called scattering of light. The light having least wavelength scatters more. The sun appears red at sunrise and sunset, appearance of blue sky it is due to the scattering of light. The colour of the scattered light depends on the size of particles. The smaller the molecules in the atmosphere scatter smaller wavelengths of light.
The amount of scattering of light depends on the wavelength of light. When light from sun enters the earth’s atmosphere, it gets scattered by the dust particles and air molecules present in the atmosphere. The path of sunlight entering in the dark room through a fine hole is seen because of scattering of the sun light by the dust particles present in its path inside the room.

Question. The colour of sky appears blue, it is due to the
A. Refraction of light through the atmosphere
B. Scattering of light by air molecules
C. Dispersion of light by air molecules
D. All the above

Answer: B

Question. At the time of sunrise and sunset
A. Blue colour scattered and red colour reaches our eye
B. Red colour scattered and blue colour reaches our eye
C. Green and blue scattered and orange reaches our eye
D. None of these

Answer: B

Question. To an astronaut in a spaceship, the colour of earth appears
A. Red
B. Blue
C. White
D. Black

Answer: B

Question. At the time of sunsise and sunset light has to travel
A. Longest distance of atmosphere
B. Shortest distance of atmosphere
C. Both A and B
D. Cannot say

Answer: A
 

♦ Answer the following Conceptual and Numerical questions

Question. Why does it take some time to see objects in a cinema hall, when we just enter the hall?

Question. Why does ray of light split when passes through prism?

Question. Explain why star twinkle, planets do not.

Question. When we see any object through the hot air over the fire, it appears to be wavy and moving slightly. Explain.

Question. Why does sky appear blue on a clear day?

Question. A star sometimes appears brighter and some other times fainter. What is this effect called? State the reason for this effect.

Question. 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.

Question. Why is red colour selected as danger signal?

Question. 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.

Question. With the help of a labeled diagram, explain why the sun appears reddish at sun-rise and sunset.

Question. (a) What is dispersion of white light? What is the cause for dispersion? Draw a diagram to show the dispersion of white light through 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?

Question. What is a)the function of iris? b) persistence of vision? C) Tyndall effect?

Question. Draw a labeled diagram of rainbow formation. Also explain the phenomena.

Question. What is meant by spectrum of white light? How can we recombine the components of white light after a prism has separated them? Draw a ray diagram to illustrate.

Question. Explain (i) sun appears to rise 2 minutes before and set 2 minutes later. (ii) sun appears oval (or flattened) at sunrise and sunset.

Question. A person is advised to wear spectacles with convex lenses. What type of defect of vision is he suffering from?

Question. Why do different components of white light deviate through different angles when passing through a triangular glass prism?

Question.  A person can comfortably read a book but finds it difficult to read the number on a bus parked 5 m away from him. Name the type of defect of vision he is suffering from. Which type of lens should he use in his spectacles to correct his vision?

Question. The sky appears dark instead of blue to an astronaut. Give reason.

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

Question. (a) What is meant by power of accommodation of an eye?

(b) A person with a myopic eye cannot see objects beyond 1.2 m directly. What should be the type of the corrective lens used? What would be its power?

Question. A person needs a lens of power – 5.5D for correcting his distant vision. For correcting his near vision, he needs a lens of power +1.5D.What is the focal length of the lens required for correcting (i) distant vision (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?

Question. The near point of a hypermetropic eye is 1 m .What is the power of the lens required to correct this defect?

Question. Calculate maximum power of accommodation of a person having normal vision.

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.

Question. The near point of a hypermetropic eye is 50 cm .Calculate the power of the lens to enable him to read a book at 40cm?

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