Summary of the Chapter-10-The Human Eye and the Colourful World with Key-Points:
- The eye's ability to adjust its focal length to focus on objects both near and far is known as accommodation.
- The minimum distance at which the eye can view objects clearly without discomfort is referred to as the near point or the least distance of distinct vision. For a young adult with normal eyesight, this distance is approximately 25 cm.
- Common vision defects include myopia, hypermetropia, and presbyopia. Myopia (near-sightedness, where distant objects are focused in front of the retina) is corrected using a concave lens with the appropriate power. Hypermetropia (far-sightedness, where close objects are focused behind the retina) is corrected with a convex lens of the correct power. As people age, the eye's ability to accommodate diminishes.
- The separation of white light into its various colors is called dispersion.
- The blue color of the sky is caused by the scattering of light.
NCERT Based MCQ with Explanation:
1. The ability of the human eye to focus on objects at different distances by adjusting the focal length of the lens is called:
a) Myopia
b) Accommodation
c) Presbyopia
d) Hypermetropia
Explanation: The eye lens changes its focal length to focus on near and distant objects, a process known as accommodation.
2. The near point of a young adult with normal vision is approximately:
a) 2.5 cm
b) 25 cm
c) 2.5 m
d) 25 m
Explanation: The minimum distance at which a normal eye can see objects clearly without strain is about 25 cm.
3. Myopia is corrected by using:
a) Convex lens
b) Concave lens
c) Cylindrical lens
d) Bifocal lens
Explanation: Myopia (near-sightedness) is corrected by using a concave lens that diverges light rays to focus on the retina.
4. Hypermetropia is also known as:
a) Near-sightedness
b) Far-sightedness
c) Astigmatism
d) Color blindness
Explanation: Hypermetropia is the inability to see nearby objects clearly, hence it is called far-sightedness.
5. What is the function of the retina in the human eye?
a) It adjusts the size of the pupil
b) It refracts light
c) It forms the image
d) It detects light and sends signals to the brain
Explanation: The retina contains light-sensitive cells that detect light and send signals to the brain via the optic nerve.
6. Which condition is characterized by the elongation of the eyeball?
a) Hypermetropia
b) Myopia
c) Presbyopia
d) Cataract
Explanation: Myopia occurs when the eyeball is elongated, causing light to focus in front of the retina.
7. The primary cause of presbyopia is:
a) Aging
b) Eye infections
c) Excessive screen time
d) Congenital defects
Explanation: Presbyopia occurs as the lens of the eye loses flexibility with age, reducing its ability to focus on nearby objects.
8. The human eye forms an image on the:
a) Cornea
b) Retina
c) Iris
d) Pupil
Explanation: The eye lens focuses light onto the retina, where the image is formed.
9. Which lens is used to correct hypermetropia?
a) Concave
b) Convex
c) Cylindrical
d) Bifocal
Explanation: Hypermetropia (far-sightedness) is corrected using a convex lens, which converges light rays onto the retina.
10. Which structure controls the size of the pupil?
a) Cornea
b) Retina
c) Iris
d) Lens
Explanation: The iris is the muscular structure that controls the size of the pupil, regulating the amount of light entering the eye.
11. What is cataract?
a) A defect of distant vision
b) Clouding of the lens
c) Excessive curvature of the cornea
d) Loss of retinal cells
Explanation: Cataract refers to the clouding of the eye’s lens, leading to blurred vision.
12. The phenomenon responsible for the blue color of the sky is:
a) Refraction
b) Dispersion
c) Scattering of light
d) Reflection
Explanation: The scattering of shorter wavelengths (blue light) by air molecules is responsible for the sky’s blue color.
13. Twinkling of stars is caused by:
a) Reflection of starlight
b) Refraction in the atmosphere
c) Dispersion of light
d) Movement of stars
Explanation: The twinkling of stars is caused by atmospheric refraction, where the light from stars is bent due to varying densities in the Earth's atmosphere.
14. Why don't planets twinkle like stars?
a) They are too bright
b) They are closer to the Earth and appear larger
c) They are solid objects
d) They emit their own light
Explanation: Planets appear as extended sources of light due to their proximity to Earth, which averages out the twinkling effect.
15. The dispersion of white light produces how many colors?
a) 5
b) 6
c) 7
d) 8
Explanation: White light disperses into seven colors: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR).
16. Which of the following conditions is corrected by bifocal lenses?
a) Myopia and presbyopia
b) Hypermetropia and cataract
c) Myopia and hypermetropia
d) Presbyopia and astigmatism
Explanation: Bifocal lenses have both concave and convex sections, used to correct myopia (near-sightedness) and hypermetropia (far-sightedness).
17. The power of a lens is measured in:
a) Meters
b) Centimeters
c) Diopters
d) Degrees
Explanation: The power of a lens, which is the reciprocal of its focal length (in meters), is measured in diopters.
18. A person who can see distant objects clearly but not nearby objects has:
a) Myopia
b) Hypermetropia
c) Presbyopia
d) Astigmatism
Explanation: Hypermetropia (far-sightedness) occurs when a person can see distant objects clearly but struggles to focus on nearby objects.
19. The least distance of distinct vision for a normal eye is called:
a) Near point
b) Far point
c) Accommodation point
d) Focal point
Explanation: The least distance of distinct vision is known as the near point, typically about 25 cm for a normal eye.
20. The scattering of light by particles in the atmosphere that causes the path of a beam of light to become visible is known as:
a) Reflection
b) Tyndall effect
c) Dispersion
d) Refraction
Explanation: The Tyndall effect is the scattering of light by small particles, making the light beam visible.
21. A person suffering from presbyopia needs which type of lenses for correction?
a) Concave
b) Convex
c) Cylindrical
d) Bifocal
22. Which structure of the eye controls the amount of light entering?
a) Retina
b) Cornea
c) Pupil
d) Iris
23. The condition where the crystalline lens of the eye becomes cloudy or opaque is called:
a) Presbyopia
b) Myopia
c) Cataract
d) Astigmatism
24. The human eye's image formation is similar to which device?
a) Microscope
b) Telescope
c) Camera
d) Magnifying glass
25. The far point of a normal eye is:
a) 25 cm
b) Infinity
c) 10 m
d) 100 cm
26. When light passes through a prism, it splits into different colors due to:
a) Reflection
b) Refraction
c) Dispersion
d) Diffraction
27. What is the cause of twinkling of stars?
a) Scattering of light
b) Dispersion of light
c) Refraction of starlight through the atmosphere
d) Reflection of light from planets
28. When light passes from air into glass, it:
a) Bends towards the normal
b) Bends away from the normal
c) Does not change direction
d) Scatters
29. The condition where both nearby and distant objects appear blurry is called:
a) Astigmatism
b) Myopia
c) Hypermetropia
d) Presbyopia
30. The structure responsible for focusing light onto the retina is:
a) Cornea
b) Iris
c) Lens
d) Pupil