CBSE Class 10 Science Human Eye And Colorful World Worksheet

Assertion and Reason

DIRECTION : In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Question. Assertion : The sky looks dark and black instead of blue in outer space.
Reason : No atmosphere containing air in the outer space to scatter sunlight.
Answer : A

Question. Assertion : The optical instruments are used to increase the size of the image of the object.
Reason : The optical instruments are used increase the visual angle.
Answer : D

Question. Assertion : Hypermetropia is the defect of the eye in which only farther objects are seen.
Reason : Hypermetropia is corrected by using converging lens.
Answer : B

Question. Assertion : A normal human eye can clearly see all the objects beyond certain minimum distance.
Reason : The human eye has capacity of adjusting the focal length of eye lens.
Answer : A

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 : Thin prisms do not deviate light much.
Reason : Thin prism have small angle A and hence, D_m = [(μ - 1)A], where μ is the refractive index of prism w.r.t. medium 1.
Answer : A

Question. Assertion : Myopia is due to the increased converging power of the eye lens.
Reason : Myopia can be corrected by using spectacles made from concave lenses.
Answer : B

Question. Assertion : A normal human eye can clearly see all the objects beyond a certain minimum distance.
Reason : The human eye has the capacity to adjust suitable the focal length of its lens to a certain extent.
Answer : B

Question. Assertion : The optical instruments are used to increase the size of the image of the object.
Reason : The optical instruments are used to increase the visual angle.
Answer : D

Question. Assertion : A white light on passing through prism splits into its component colours as such that the red light emerges nearest to the base of the prism.
Reason : Wavelength of red light is more than other component colours and hence, red light deviates least.
Answer : D

Question. Assertion : The resolving power of a telescope is more if the diameter of the objective lens is more.
Reason : Objective lens of large diameter coileds more light.
Answer : A

Question. Assertion : The twinkling of stars is due to the fact that refractive index of the earth’s atmosphere fluctuates.
Reason : 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

Very Short Answer type Questions

Question. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Answer : Ciliary muscles can contract the lens of human eye to a certain limit because of which a person with normal vision can see the nearby objects clearly only if placed at 25 cm but if the object is placed closer to the eye than it cannot see the objects clearly.

Question. What is meant by power of accommodation of the eye?
Answer : The ability of the eye to focus the distant objects as well as the nearby objects on the retina by changing the focal length of the eye lens is called power of accommodation.

Question. Why do stars twinkle?
Answer : Stars twinkle due to atmospheric refraction of light from the stars and changing density of air around the earth.

Question. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected? 
Answer : A student is suffering with the eye defect named myopia, in this defect person can see nearby objects clearly but cannot see far off objects distinctly. It can be corrected by using concave lens.

Question. Why does the sun appear reddish early in the morning?
Answer : When the sun rises early in the morning (or set in the evening), the light from sun travels through the thicker layer of air and larger distance of the atmosphere surrounding the earth. Hence the blue light scatters the most but red light does not scatters and reaches our eyes.

Question. What is the far point and near point of the human eye with normal vision?
Answer : The far point is infinity and the near point is 25 cm of the human eye with normal vision.

Question. What happens to the image distance in the eye when we increase the distance of an object from the eye?
Answer : The image distance in the eye remains the same. On increasing the distance of an object from the eye, the focal length of the eyes changes due to ciliary muscles which helps an eye to focus the object image on retina.

Question. Explain why the planets do not twinkle.
Answer : Planets are much closer to earth and behave like extended source.

Question. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Answer : A person with a myopic eye can use concave lens to restore proper vision.

Question. Why does the sky appear dark instead of blue to an astronaut?
Answer : In space there are no particles, air, gases, water droplets etc., present to scatter the light. So when the astronauts look at the sky in the space, there is no light entering our eyes, hence it appears dark 

Question. Name the three phenomenon of light responsible for the formation of rainbow in the sky.
Answer : Refraction, dispersion and internal reflection of light.