📘 Welcome
Hi User, you have selected Read Mode.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
Q1. The sky appears blue mainly due to scattering by
The sky appears blue mainly due to scattering of sunlight by air molecules (oxygen and nitrogen). These molecules are much smaller than the wavelength of light. According to Rayleigh scattering, they scatter blue light (shorter wavelength) much more than red light (longer wavelength). This scattered blue light reaches our eyes from all directions, making the sky appear blue.
Q2. Light from the Sun near the horizon passes through
Light from the Sun near the horizon passes through thicker layers of air compared to when the Sun is overhead. At sunrise and sunset, the Sun is near the horizon, so sunlight has to travel a longer path through the atmosphere. This longer path causes more scattering of blue light, making the Sun appear reddish.
Q3. Near the horizon, most of the blue light is
Near the horizon, most of the blue light is scattered away by air molecules and particles. Because sunlight travels through a thicker layer of atmosphere at sunrise and sunset, blue light (shorter wavelength) is scattered in all directions and does not reach our eyes directly. This leaves red and orange light to reach us, making the Sun appear reddish.
Q4. The image formed by the human eye is formed on the
The image formed by the human eye is formed on the retina, which is the light-sensitive layer at the back of the eye. The cornea and eye lens focus light onto the retina, where photoreceptor cells (rods and cones) convert it into electrical signals. These signals are then sent to the brain through the optic nerve.
Q5. In old age, the eye loses its power of
In old age, the eye loses its power of accommodation—the ability to change the focal length of the lens to focus on nearby objects. This happens because the eye lens becomes harder and less flexible, and the ciliary muscles weaken. This condition is called presbyopia and typically begins around age 40.
Q6. Objects placed closer than the near point appear
Objects placed closer than the near point (about 25 cm for a normal adult eye) appear blurred. The eye cannot focus on objects that are too close because the lens cannot become thick enough to provide the required converging power. The image falls behind the retina, resulting in blurred vision. This is why we cannot see objects clearly if they are too close to our eyes.
Q7. The eye lens changes its curvature due to
The eye lens changes its curvature due to the action of the ciliary muscles. When these muscles contract, they release tension on the suspensory ligaments, allowing the lens to become thicker and more curved (for near vision). When they relax, the lens becomes thinner and flatter (for distant vision). This change in curvature is called accommodation.
Q8. A person suffering from myopia cannot see
A person suffering from myopia (near-sightedness) cannot see distant objects clearly. They can see nearby objects clearly because the image of distant objects is formed in front of the retina instead of on it. This happens because the eyeball is too long or the lens is too curved. Myopia is corrected using concave lenses.
Q9. The sky appears dark to astronauts because
The sky appears dark to astronauts because there is no atmosphere in space to scatter sunlight. On Earth, the atmosphere scatters blue light, making the sky appear blue. In space, without an atmosphere, there are no particles to scatter light, so the sky appears black even when the Sun is shining.
Q10. Near the horizon, sunlight reaching our eyes is mainly of
Near the horizon, sunlight reaching our eyes is mainly of longer wavelength (red and orange). As sunlight travels through a thicker layer of atmosphere, blue light (shorter wavelength) is scattered away. Red light (longer wavelength) is scattered the least and reaches our eyes, making the Sun appear reddish at sunrise and sunset.
Q11. At sunrise, sunlight travels
At sunrise, sunlight travels a longer atmospheric path because the Sun is near the horizon. The light must pass through a thicker layer of the atmosphere compared to when the Sun is overhead. This longer path causes more scattering of blue light, leaving red and orange light to reach our eyes, making the Sun appear reddish.
Q12. Stars appear as
Stars appear as point sources of light because they are extremely far away from Earth. At such vast distances, even the largest stars appear as just a point of light (a point source). This is why stars twinkle—atmospheric refraction affects this single point of light, causing it to flicker. Planets are extended sources (small disks) and do not twinkle.
Q13. Dispersion occurs when light passes through
Dispersion occurs when light passes through a prism. A prism has inclined (non-parallel) surfaces that cause different colours (wavelengths) of light to refract by different amounts. This separates white light into its seven constituent colours (VIBGYOR). Lenses and mirrors do not cause dispersion—they focus or reflect light.
Q14. Atmospheric scattering is more effective for
Atmospheric scattering is more effective for shorter wavelengths (like blue and violet light). According to Rayleigh scattering, the amount of scattering is inversely proportional to the fourth power of wavelength. This means shorter wavelengths are scattered much more than longer wavelengths. This is why the sky appears blue (blue is scattered more) and why the Sun appears red at sunset (red is scattered less).
Q15. The far point of a normal eye is
The far point of a normal eye is at infinity. This means a normal eye can see objects at any distance (from the near point of 25 cm to infinity) clearly without straining. The eye lens becomes thin and flat enough to focus parallel rays from distant objects exactly on the retina.
Q16. Blue light has
Blue light has a short wavelength (about 400-450 nm) among visible colours. Shorter wavelengths are scattered more by air molecules, which is why the sky appears blue. In contrast, red light has a longer wavelength (about 700 nm) and is scattered less.
Q17. For a normal young adult, the near point is about
For a normal young adult, the near point (least distance of distinct vision) is about 25 cm. This is the closest distance at which the eye can see an object clearly without straining. For children, the near point is smaller (about 15-20 cm), and for elderly people, it increases due to presbyopia.
Q18. Blue colour of the sky is caused by
The blue colour of the sky is caused by scattering of sunlight by air molecules (Rayleigh scattering). Blue light (shorter wavelength) is scattered more than other colours. This scattered blue light reaches our eyes from all directions, making the sky appear blue. Without scattering, the sky would appear black.
Q19. Myopia is also known as
Myopia is also known as short-sightedness or near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects clearly. This happens because the image of distant objects is formed in front of the retina. Myopia is corrected using concave lenses.
Q20. Scattering of light explains
Scattering of light explains both the blue colour of the sky and the red colour of the Sun at sunrise and sunset. During the day, blue light is scattered more, making the sky blue. At sunrise/sunset, sunlight travels through more atmosphere, and blue light is scattered away, leaving red light to reach our eyes. Both phenomena are caused by the same scattering process.
Q21. The phenomenon responsible for reddening of the Sun is
The phenomenon responsible for the reddening of the Sun at sunrise and sunset is scattering. At these times, sunlight passes through a thicker layer of the atmosphere. Blue light is scattered away, leaving red light (which is scattered the least) to reach our eyes. This makes the Sun appear reddish.
Q22. The normal eye can see distant objects clearly when the image is formed
The normal eye can see distant objects clearly when the image is formed exactly on the retina. In a normal eye, the cornea and lens focus light precisely onto the retina. If the image forms in front of or behind the retina, the vision becomes blurred. This precise focusing is what gives us clear vision.
Q23. The least distance of distinct vision is also called
The least distance of distinct vision is also called the near point. It is the closest distance at which the eye can see an object clearly without straining. For a normal adult eye, the near point is about 25 cm. Objects closer than this appear blurred because the eye cannot accommodate enough to focus them.
Q24. At noon, the Sun appears white because
At noon, the Sun appears white because very little blue and violet light is scattered. At this time, sunlight travels the shortest distance through the atmosphere. Since the path is short, very little scattering occurs, and all colours of sunlight reach our eyes almost equally. The combination of all colours appears white.
Q25. When object distance increases, the image distance in the eye
When object distance increases, the image distance in the eye remains constant. This is because the retina is fixed at a constant distance from the lens. To maintain clear vision, the eye changes the focal length of the lens (accommodation) rather than changing the image distance. The image is always formed on the retina, regardless of the object distance.
Q26. Which defect requires convex lens correction?
Hypermetropia (far-sightedness) requires convex lens correction. In hypermetropia, the image of nearby objects is formed behind the retina. A convex lens converges light before it enters the eye, moving the focus forward onto the retina. Convex lenses have positive power. Myopia is corrected with concave lenses.
Q27. Splitting of white light into its component colours is called
Splitting of white light into its component colours is called dispersion. This occurs when white light passes through a prism or raindrops. Different colours have different wavelengths and speeds in the medium, so they refract by different amounts. The resulting spectrum consists of seven colours (VIBGYOR).
Q28. A person suffering from hypermetropia cannot see
A person suffering from hypermetropia (far-sightedness) cannot see nearby objects clearly. They can see distant objects clearly. In hypermetropia, the image of nearby objects is formed behind the retina because the eyeball is too short or the lens is too flat. It is corrected using convex lenses.
Q29. The pupil appears black because
The pupil appears black because no light comes out of it. Light enters the eye through the pupil and is absorbed by the dark choroid layer and retina inside the eye. Since very little light is reflected back out, the pupil looks black. This is similar to why a hole in a box appears black—light goes in but does not come out.
Q30. In myopia, the image of distant objects is formed
In myopia, the image of distant objects is formed before (in front of) the retina. This happens because the eyeball is too long or the lens/cornea is too curved. The excessive convergence causes light to focus before reaching the retina, resulting in blurred distant vision. Myopia is corrected using concave lenses.
Q31. Hypermetropia is also known as
Hypermetropia is also known as far-sightedness because a person with hypermetropia can see distant objects clearly but cannot see nearby objects clearly. In hypermetropia, the image of nearby objects is formed behind the retina. It is corrected using convex lenses.
Q32. Myopia is corrected using a
Myopia is corrected using a concave lens. A concave lens diverges (spreads out) light rays before they enter the eye, reducing the excessive convergence caused by myopia. This moves the focus of distant objects from in front of the retina to the retina. Concave lenses have negative power.
Q33. The change in focal length of the eye lens is caused by
The change in focal length of the eye lens is caused by the ciliary muscles. When they contract, the lens becomes thicker (shorter focal length) for near vision. When they relax, the lens becomes thinner (longer focal length) for distant vision. This ability to change focal length is called accommodation.
Q34. Which part controls the amount of light entering the eye?
The iris controls the amount of light entering the eye by adjusting the size of the pupil. In bright light, the iris contracts the pupil (makes it smaller) to reduce light entry. In dim light, the iris dilates the pupil (makes it larger) to allow more light in. The iris is the coloured part of the eye.
Q35. Light from the Sun overhead travels
Light from the Sun overhead travels a shorter distance through the atmosphere compared to when the Sun is near the horizon. At noon, the Sun is directly overhead, so sunlight passes through the least amount of atmosphere. This results in less scattering, making the Sun appear white.
Q36. The function of retina is to
The function of the retina is to form an image by detecting light and converting it into electrical signals. The retina contains photoreceptor cells (rods and cones) that respond to light. These cells generate electrical signals that are sent to the brain through the optic nerve. The brain then interprets these signals as visual images.
Q37. In hypermetropia, the image of nearby objects is formed
In hypermetropia, the image of nearby objects is formed behind the retina. This happens because the eyeball is too short or the lens is too flat, causing light to converge too slowly. As a result, nearby objects appear blurry. Hypermetropia is corrected using convex lenses, which converge light more.
Q38. The ability of the eye to focus near and distant objects is called
The ability of the eye to focus on both near and distant objects is called accommodation. This is achieved by the ciliary muscles changing the shape (and focal length) of the eye lens. For near objects, the lens becomes thicker. For distant objects, the lens becomes thinner. This adjustment ensures clear vision at all distances.
Q39. The Sun appears reddish at sunset because blue light is
The Sun appears reddish at sunset because blue light is scattered away by air molecules and particles. At sunset, sunlight travels through a thicker layer of atmosphere. Blue light (shorter wavelength) is scattered in all directions and does not reach our eyes directly. Red light (longer wavelength) is scattered less and reaches our eyes, making the Sun appear reddish.
Q40. The reddish appearance of the Sun near horizon is due to
The reddish appearance of the Sun near the horizon is due to longer wavelengths (red and orange) reaching our eyes. At sunrise and sunset, blue light is scattered away. Red light, having a longer wavelength, is scattered the least and travels straight to our eyes. This makes the Sun appear reddish or orange.
Q41. Planets do not twinkle because they are
Planets do not twinkle because they are extended sources of light (small disks). Because planets are closer to Earth than stars, they appear as small discs rather than points of light. Light from different parts of the disc undergoes different amounts of atmospheric refraction, and these variations average out, so the planet does not appear to twinkle.
Q42. Reddening of the Sun at sunrise and sunset is due to
Reddening of the Sun at sunrise and sunset is due to scattering of light. At these times, sunlight passes through a thicker layer of the atmosphere, and blue light is scattered away. Red light (which is scattered the least) reaches our eyes, making the Sun appear reddish. This is the same scattering process that makes the sky blue during the day.
Q43. Stars twinkle due to
Stars twinkle due to atmospheric refraction. As starlight passes through different layers of the atmosphere with varying densities, it is continuously refracted. This causes the apparent position and brightness of the star to change rapidly, making it appear to twinkle. Planets do not twinkle because they are extended sources.
Q44. Which colour is scattered most by air molecules?
Blue light is scattered most by air molecules. According to Rayleigh scattering, the amount of scattering is inversely proportional to the fourth power of wavelength. Blue light has a shorter wavelength, so it is scattered much more than red light. This is why the sky appears blue—blue light is scattered in all directions.
Q45. The eye lens is
The eye lens is convex (biconvex), meaning it is thicker in the middle and thinner at the edges. A convex lens converges light rays. The eye lens, along with the cornea, focuses light onto the retina. The convex shape allows the lens to change its curvature for accommodation (near and distant vision).
Q46. Which defect requires concave lens correction?
Myopia (near-sightedness) requires concave lens correction. In myopia, the image of distant objects is formed in front of the retina. A concave lens diverges light before it enters the eye, reducing the excessive convergence and moving the focus onto the retina. Concave lenses have negative power.
Q47. Presbyopia occurs mainly due to
Presbyopia occurs mainly due to old age. As a person ages (usually after age 40), the eye lens becomes harder and less flexible, and the ciliary muscles weaken. This reduces the eye’s power of accommodation, making it difficult to focus on nearby objects. Presbyopia is a natural part of ageing and is corrected using reading glasses.
Q48. Red light has
Red light has a longer wavelength (about 700 nm) among visible colours. This longer wavelength causes red light to be scattered less by air molecules (Rayleigh scattering), which is why red light can travel long distances and is used for danger signals. Red light is at the opposite end of the spectrum from violet light.
Q49. Accommodation of the eye occurs by adjusting the
Accommodation of the eye occurs by adjusting the focal length of the eye lens. The ciliary muscles change the shape of the lens—making it thicker (shorter focal length) for near vision and thinner (longer focal length) for distant vision. This adjustment ensures clear vision at different distances.
Q50. Hypermetropia is corrected using a
Hypermetropia is corrected using a convex lens. In hypermetropia, the image of nearby objects is formed behind the retina. A convex lens converges light before it enters the eye, moving the focus forward onto the retina. Convex lenses have positive power. Myopia is corrected with concave lenses.