CBSE Class 10 Science The Human Eye and the Colourful World Assignment Set A

Question. To get line spectrum, the substances are excited in their
(a) solid state
(b) molecular state
(c) gaseous state
(d) atomic state
Answer : D

Question. Sometimes blurred and less sharply defined images are formed. This defect is called
(a) Chromatic aberration
(b) Spherical aberration
(c) Blurred lens
(d) None of the above
Answer : B

Question. A prism ABC (with BC as base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in figure. In which of the following cases, after dispersion, the sixth colour from the top corresponds to the colour of the sun?

Question. A glass slab is placed over a page on which the word VIBGYOR is printed with each letter in corresponding colour. Then, which of the following is correct?
(a) The images of all the letters will be in the same place as that on paper
(b) Letter V is raised more
(c) Letter R is raised more
(d) None of the above
Answer : B

Question. The following one is not a primary colour
(a) Yellow
(b) Red
(c) Green
(d) Blue
Answer : A

Question. A person cannot see objects clearly which are nearer than 75 cms from his eyes, the disease he suffering from is
(a) Astigmatism
(b) Myopia
(c) Hypermetropia
(d) Presbyopia
Answer : C

Answer : D

Question. A person with a myopic eye cannot see object beyond -1.2m distinctly. The power of the corrective lens used to restore proper vision is
(a) -0.83 D
(b) -0.92 D
(c) +0.21D
(d) +0.91D
Answer : A

Question. Fraunhofer lines in the sun’s spectrum are present because
(a) Vapours of certain elements present in the atmosphere absorb certain colours
(b) The temperature of the sun is very high 
(c) The sun does emit certain light
(d) Certain elements present in the sun interfere
Answer : D

Question. When a mirror is rotated an angle the reflected ray moves through double that angle, the instrument based on the above principle is
(a) Periscope
(b) Odometer
(c) Refractometer
(d) Sextant
Answer : D

Question. The splitting of white light into several colours on passing through a glass prism is due to
(a) refraction
(b) reflection
(c) interference
(d) diffraction
Answer : A

Question. At sun rise or at sun set the sun appears to be reddish while at mid-day it looks white. This is because
(a) Scattering due to dust particles and air molecules causes this phenomenon
(b) The sun is cooler at sun rise or at sunset
(c) Refraction causes this phenomenon
(d) Diffraction sends red rays to the earth at these times.
Answer : A

Question. The frequency of light whose wavelength is 5000 Ac is
(a) 15#1013 cycles per second
(b) 5000 cycles per second
(c) 6#1014 cycles per second
(d) 15#1016 cycles per second
Answer : C

Question : Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?
(a) Dispersion of light
(b) Scattering of light
(c) Total internal reflection of light
(d) Reflection of light from the earth.
Answer : B

Question : While performing the experiment to trace the path of a ray of light passing through a glass prism, four students marked the incident ray and the emergent ray in their diagrams in the manner shown below.

The correct path of the rays has been shown by:
(a) I
(b) II
(c) III
(d) IV
Answer : C

Matching Questions

Question. 

Answer : A-s, B-r, p, C-q, D-q

Answer : A-q, B-p, C-r, D-s

Answer : (a) A-s, r, B-r, p, C-q, D-q

Answer : (a) A-t, B-p, C- q, s, D-r

Very Short Answer

Question :  What is the relation between intensity of scattered light and its amplitude? 

Answer :  The intensity of scattered light is directly proportional to the square of the amplitude 

a. of scattered light, i.e 

 

means greater the amplitude greater will be intensity of refraction and vice versa.

Question : Which phenomenon is responsible for making the path of light visible?
Answer :  Tyndall effect is responsible for making the path of light visible. 

Question : What will the color of the sky be for an astronaut staying in the international space station orbiting the earth?
Answer :  For an astronaut staying in the international space station orbiting the Earth the color of the sky will be black because the light reaching it does not scatter.

  

Short Answer 

 

Question : Why are we not able to see the object clearly for some time when we enter bright light to a room with dim light ? 

Answer :  The pupil of the eye acts as a variable aperture whose size can be varied with the help of the iris. When the light is very bright, the iris contracts the pupil to allow less light to enter the eye. However in dim light the iris expands the pupil to allow more light to enter the eye. When we enter from a bright light area to a dim light area, the pupil is  not able to expand quickly to allow more light into the eye. We are therefore not able to see the objects in dim light room momentarily. 

Question : When white light passes through a glass prism; seven colors namely red, orange, yellow, green, blue, indigo and violet are seen on the white screen. All these colors have different angles of deviation. Explain why?
Answer :  Speed of color in a medium depends upon its wavelength. All the colors have different wavelength. The red color has the longest wavelength and violet color has the last wavelength. Therefore, red color has the highest speed in the glass prism and the violet color has the lowest speed in the glass prism. Hence, all colors of white light are refracted by different amounts while passing through the glass prism. Therefore, all the colors have different angles of deviations. 

Question : (a) What is hypermetropia?
(b) What are the two causes of the defect of vision?
(c) How can this defect of the eye be corrected? Illustrate your answer by drawing ray diagrams to show the formation of image by
(i) a hypermetropic eye
(ii) a hypermetropic eye corrected with a suitable lens.
Answer : (a) Hypermetropia: It is also called long-sightedness. The person with this eye defect can see far off objects but cannot see nearby objects clearly. The image is formed beyond retina.
(b) Two causes
(i) Focal length of the lens increases
(ii) Eye ball becomes smaller
(c) Correction: It can be corrected by using a convex lens. It is a converging lens which shifts the image of the object on the retina.

Question : What is hypermetropia? State the two causes of hypermetropia. With the help of ray diagram show:
(i) the eye defect hypermetropia.
(ii) correction of hypermetropia by using a lens
Ans. Hypermetropia: Defect of a vision in which a person can see distant objects clearly but cannot see nearby objects clearly.
Causes: (a) Focal length of the eye lens is too large.
(b) Eye ball has become too small.

Long Answer

Question : A narrow beam PQ of white light is passing through a glass prism ABC as shown in the diagram.
(i) Write the name and cause of the phenomenon observed.
(ii) Where else in nature is this phenomenon observed?
(iii) Based on this observation, state the conclusion which can be drawn about the constituents of white light.