CBSE Class 10 Physics The Human Eye And Its Colorful World Assignment

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The Human Eye And Its Colourful World Class 10 Physics Assignment Pdf

Class 10 Physics students should refer to the following printable assignment in Pdf for The Human Eye And Its Colourful World in standard 10. This test paper with questions and answers for Grade 10 Physics will be very useful for exams and help you to score good marks

Class 10 Physics Assignment for The Human Eye And Its Colourful World

Question : Which of the following colors is least scattered by fog, dust of smoke?
(a) Violet
(b) Blue
(c) Red
(d) Yellow
Answer :  C


Question : Which of the following statements is correct regarding the propagation of light of different colors of white light in air?
(a) Red light moves fastest.
(b) Blue light moves faster than green light.
(c) All the colors of the white light move with the same speed
(d) Yellow light moves with the mean speed as that of the red and the violet light.
Answer :  C


Question : In the following diagram, the path of a ray of light passing through a glass prism is shown:

Class 10 Science Human Eyes And Colourful World_9

In this diagram the angle of incidence, the angle of emergence and the angle of deviation respectively are (select the correct option):
(a) X, R and T
(b) Y, Q and T
(c) X, Q and P
(d) Y, Q and P
Answer :  D


Question : Twinkling of stars is due to atmospheric
(a) Ultraviolet radiations are absorbed in the atmosphere.
(b) refraction of light by different layers of varying refractive indices
(c) scattering of light by dust particles
(d) internal reflection of light by clouds.
Answer :  B


Question : A student traces the path of a ray through a glass prism for four different values of angle of incidence. On analyzing the diagrams, he is likely to conclude that the emergent ray
(a) is always parallel to the incident ray.
(b) Is always perpendicular to the incident ray
(c) Is always parallel to the refracted ray
(d) Always bends at an angle to the direction of incident ray.
Answer :  D


Question :  A person cannot see distinctly any object placed beyond 40cm from his eyes. Calculate the power of the lens which will help him to see distant objects clearly. 
(a) -2.5 Dioptre
(b) -1.5 Dioptre
(c) +2 Dioptre
(d) +1 Dioptre
Answer : D

Question : What is spectrum- 
(a) None of these
(b)  The band of 5 colours
(c) The band of 6 colours
(d) The band of 7 colours
Answer : D 
Explanation: When a white light is passed through a prism it gets split into combination of seven colours which is known as the spectrum. The colors of the spectrum of white light are those seen in a rainbow. They are usually named in order as: red, orange, yellow, green, blue, indigo and violet.
 
Question :  Danger signals are red in colour because 
(a) red colour is least scattered
(b) red colours is most scattered
(c) wavelength of red colour is less than that of other colour
(d) red colour looks attractive
Answer : A 
Explanation: Red colour scattered the least when strikes by the small particle of fog and smoke because it has the maximum wavelength (visible spectrum). Hence at large distance also, we can see the red colour clearly.
 
Question :  The colour that is scattered the least by the tiny particles and the atoms/ molecules of the atmosphere is 
(a) Red
(b) Green
(c) Violet
(d) yellow
Answer : A
Explanation: Scattering of light decreases with increase in wavelength. Red colour scattered the least when strikes the small particle of fog and smoke because it has the maximum wavelength (visible spectrum).
 
Question :  Which of the following phenomenon contributes significantly to the reddish appearance of the sun at sunrise or sunset? 
(a) Total internal Reflection
(b) Dispersion of light
(c) Reflection of light from the earth
(d) Scattering of light
Answer :  D
Explanation: While sunset and sunrise, the colour of the sun and its surrounding appear red. During sunset and sunrise, the sun is near horizon, and therefore the sunlight has to travel larger distance in atmosphere. Due to this most of the blue light (shorter wavelength) are scattered away by the particles. The light of longer wavelength (red colour) will reach our eye. This is why sun appear red in colour. 
 
 

Very Short Answers



Question :  Define power of accommodation? 
Answer :  The ability of the eye to focus objects lying at different distances clearly on the retina by changing the focal length of the eye lens with the help of ciliary muscles is called the power of accommodation of the eye. 
 
 
Question :  Why do we observe difference in colours of the Sun during sunrise, sunset and noon? 
Answer :  This is because of scattering of light near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles present in the atmosphere during sunrise and sunset. So, the light that reaches our eyes is of longer wavelength
(e.g. red). This gives rise to the reddish appearance of the sky. But during the day sun appears white as sun is near the surface of earth nearly overhead, thus the sunlight passes through much smaller distance and thus the scattering is much less and sun appears white. 
 
 
Question :  What part of the eye can be denoted after death ? 
Answer :  The cornea from dead body is removed within 6 hours of the death and transplanted in the eyes of blind person with opaque cornea. His opaque cornea is replaced by transparent cornea of dead person.  
 

Question : Why is the sun visible to us 2 minutes before actual sunrise and 2 minutes after actual sunset?
Answer :  We are able to see the sun 2 minutes before actual sunrise and 2 minutes after actual sunset because sunrays undergo atmospheric refraction as they travel from an optically rarer medium to an optically denser medium when they enter the earth’s atmosphere due to which they are refracted downwards and hence appear to be above the horizon.

Question :  Name the part of an eye which is equivalent to following parts in a camera.
i. diaphragm
ii. photographic plate
Answer :
i. Iris of an eye = diaphragm in a camera.
ii. Retina of an eye = photographic plate in a camera. 
 

Question : What is colour blindness? 
Answer : Colour-blindness is the inability to distinguish the differences between certain primary colours. This condition results from an absence of color-sensitive pigment in the cone cells of the retina, the nerve layer at the back of the eye. 


Question : Bees are able to see ultraviolet light. Comment. 
Answer : The bees are able to see ultraviolet light becuase the retina of bees contains cone cells that are sensitive to ultraviolet light. 


Question : Why do stars appear higher than their actual position?
Answer :  Stars appear higher than their actual position as starlight undergoes refraction continuously on entering earth’s atmosphere and bends towards the normal.


Question : On the basis of which observation did Newton conclude that sunlight is made up of seven colours?
Answer :  The observation on the basis of which Newton concluded that sunlight is made up of seven colours was the emergence of white light from the other side of a second identical and inverted prism placed alongside first prism and through which all colours of the spectrum were passed.


Question : Why is the colour of the clear sky blue?
Answer :  The blue colour of sky is due to the scattering of sunlight by the large number of molecules such as fine dust particles, gases, water vapour etc present in the earth’s atmosphere.
As the size of the scatterer is much smaller than the wavelength of light, light of smaller wavelength such as blue is scattered the most as compared to light of longer wavelength.


Short Answers


Question : Use scattering of light? phenomenon to explain why (A) the Sun appears reddish at sun-rise, and (B) the clear sky appears blue.
Answer :  Scattering of light is the phenomenon of change in the direction of light on striking an obstacle like an atom, a molecule, dust particle, water droplet etc.
(A) At the time of sunrise, the sun is near the horizon due to which sunrays have to travel much larger part of the atmosphere. Most of the blue light is thus scattered away. The red colour having the longest wavelength is scattered the least and hence enters our eyes.
(B) The blue colour of sky is due to the scattering of light by the large number of molecules and fine dust particles present in the earth’s atmosphere which mostly scatter light of shorter wavelength such as blue as the size of the scatterer is much smaller than the wavelength of light. 

Question :  What are rods and cones ? Give their action. 
Answer :   Sensitive portion of retina has large number of cells; one rod shaped and other cones shaped. Rod shaped cells are sensitive to the intensity or brightness of the light whereas cone shaped cells are sensitive to colours. Different animals have different type of cells. Bee has certain cone shaped cells which are sensitive to light beyond violet. This part of spectrum beyond violet called ultra violet region can be seen by bee whereas human being cannot see ultra-violet region. Chickens have very few rod
shaped cells and hence their eyes are not able to see less bright light. Hence they stroll only in bright light. They come late in the morning and go back earlier in the evening.
Most of its cells are cone shaped and hence are very sensitive to colours.
 
Question : Study the diagram given below and answer the questions that follow: 
T-8
i. Which defect of vision is represented in this case? Give reason for your answer.
ii. What could be the two causes of this defect?
iii. With the help of a diagram show how this defect can be corrected by the use of a suitable lens?
Answer : i. This defect is hypermetropia (Far- sightedness) as the image of a near point is formed beyond the retina.
ii. The two possible causes of the defect are (a) Size of eyeball become smaller. (b) The focal length of the lens increases.
iii. This defect can be corrected by using a convex lens of suitable focal length. The diagram showing correction of this defect by using convex lens of suitable focal length is shown below.
T-9
 
 
Question : A beam of white light falling on a glass prism gets split up into seven colours marked 1 to 7 as shown in the diagram. 
T-10
i. The colour at position marked 3 and 5 are similar to the colour of the sky and the colour of gold metal, respectively. Is the above statement made by the student correct or incorrect justify?
ii. Which of the above shown positions corresponds approximately to the colour of
a. a brinjal,
b. danger signal,
c. neel which is applied to clothes,
d. orange.
Answer : i. No the satement made by the student is incorrect as because 3 refers to yellow which is the colour of gold metal and 5 refers to blue colours of the spectrum which is the colour of sky.
ii. a. 7 which is violet
b. 1 which it red
c. 6 which is indigo
d. 2 which is orange
 

Long Answers


Question :  What is atmospheric refraction? Use this phenomenon to explain the following natural events. 
i. Twinkling of stars.
ii. Advanced sunrise and delayed sunset.
Draw diagrams to illustrate your answers.
Answer :  The density of the atmosphere, as we know goes on decreasing as the distance above the sea level increases. Hence, the refractive index of a layer of air level goes on changing with distance. Due to this refraction takes place when light passes through the earth's atmosphere. This phenomenon is called as atmospheric refraction.
i. Twinkling of stars: It is due to atmospheric refraction of star light. Due to variations in the refractive indices of the various layers of air, the light from a star passing through the atmosphere changes its path from time to time and therefore the amount of light reaching the eye is not always the same. This increase or decrease in the intensity of light reaching the eye results in the change in apparent position of the star. Hence, the stars appear to be twinkling.
ii. Advanced sunrise and delayed sunset: The figure below shows the actual position of the sun S at the time of sunrise and S' the apparent position of sun. The advanced sunrise and delayed sunset is because of atmospheric refraction.
T-11
The light rays starting from the Sun travel from rarer to denser layers. They bend more and more towards the normal as it moves in denser medium.
However, an observer on earth sees an object in the direction of the rays reaching his eyes. The Sun which is actually in a position S below the horizon appears in the position S' above the horizon for him. Thus, the Sun appears to rise early by about 2 min. Similarly, during sunset due to atmospheric refraction, the observer on earth sees the sunset than it would be without atmosphere. Thus, sunset late by about 2 min than its actual timings. These phenomena together increases the length of the day by about 4 min. 
 
 

Question : (a) Draw a labeled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.
(b) A star appears slightly higher (above) than its actual position in the sky. Illustrate it with the help of a labelled diagram.

Answer : (a)

Class 10 Science Human Eyes And Colourful World_7

(b) Light from a star is refracted as it leaves vacuum and enters the earth’s atmosphere. Air at higher altitudes is rarer and is denser nearer to the earth’s surface. Thus when light coming from the star comes down, the dense air bends the light more. Due to this refraction of star’s light, the star appears to be at a higher position.

Class 10 Science Human Eyes And Colourful World_8


 

Question : State the cause of dispersion of white light passing through a glass prism. How did Newton show that white light of Sun contains seven colors using two identical glass prisms? Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the focus of the first prism.
Answer :  White light is a mixture of lights of seven colors, red, orange, yellow, green, blue, indigo and violet. The dispersion of white light occurs because colors of white light travel at different speeds through the glass prism. The amount of refraction depends on the speed of colored light in glass. When white light consisting of seven colors falls on a glass prism, each color in it is refracted by a different angle, with the result that seven colors are spread out to form a spectrum. The red light bends the least, while violet bends the most.

Newton’s experiment with two identical prisms:
* When a beam of white light is passed through a glass prism, a band of seven colors is formed on a white screen. This band of seven colors is called spectrum of white light.
* Newton showed that the seven colored lights of the spectrum can be recombined to give back white light.
* First he tried to split the colors of the spectrum of white light using a prism.
* He then placed a second identical prism in an inverted position with respect to the first prism. This allowed all the colors of the spectrum to pass through the second prism. He found a beam of white light emerging from the other side of the second prism.

Class 10 Science Human Eyes And Colourful World_10


Question : ‘The human eye is like a camera’. Justify the statement.

Question : The eye lens forms an inverted real image of the object on the retina. But we perceive objects as they are. How is it possible?

Question : We are not able to see objects clearly for some time when we enter from bright light to a room with dim light. After sometime, however, we are able to see things in the dim-lit room.Why is it so?

Question : A person is not able to read the book comfortably but is able to read the matter written at far-off distance.

Name the defect of vision he is suffering from.

What is the cause for this defect?

With the help of the ray diagram show that how can this defect be corrected.

Question : Why is a normal eye not able to see clearly the objects placed at 10 cm?

Question : What is hypermetropia? Draw ray diagrams to show the image formation of an object by:

{i} Hypermetropic eye,

{ii} Correction made with a suitable lens for hypermetropic eye.

Question : The ciliary muscles of a normal eye are there in:

a) most relaxed

b) most contracted state

In which of the two cases is the focal length of the lens more. Explain.

Question : What is cataract? How is it corrected?

Question : The power of accommodation of the eye usually decreases with ageing. Why does it happen? How is it corrected?

Question : Which angle in a prism is known as the angle of the prism.

Question : Why do we see the seven colours when white light disperses? Which colour deviates the least?

Question : Trace the path of a ray of light passing through a glass prism and label it.

Question : A monochromatic beam of light does not split when it passes through a prism while a beam of White light does. How are the two cases different from each other? Explain.

Question : Name the scientist who used a glass prism to obtain the spectrum of sunlight for the first time. 
 
Question : The near point of a hypermetropic person is 75cm.Calculate the focal length and power of the lens used in his spectacles.
 
Question : Far point of a normal human eye is at infinity. Will the far point of a myopic person be at infinity or less than infinity?
 
Question : The far point of a myopic person is 150cm in front of eye. What is the nature and power of the lens required to correct this problem?
 
Question : With the help of a diagram show the arrangement of prisms so that a beam of light entering into the arrangement emerges out as a beam of white light.
 
Question : A glass prism splits a beam of white light into seven colours but a glass slab does not. Why?
 
Question : Name the three phenomenon of light responsible for the formation of Rainbow. Draw a labeled diagram for the same.
 
Question : Can we also see a rainbow on a sunny day? Give a situation to support your answer.
 
Question : Where is the rainbow formed in the sky with respect to sun? Diagrammatically support your answer.
 
Question : We generally observe the apparent random wavering or flickering of objects seen through a turbulent stream of hot air rising above a fire or a radiator. Explain the phenomenon.
 
Question : Why do stars twinkle but planets do not?
 
Question : The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset. Why? Draw a labeled diagram for the same.
 
Question : What is tyndal effect.
 
Question : Discuss the phenomenon of scattering.
 


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