Subject: Science (Physics) - Natural Phenomena
Target Syllabus: Reflection of Light, Refraction, Lenses, Human Eye, Defects of Vision, Prism, Dispersion, and Scattering.
This article contains 100 Important VSAQ (Very Short Answer Questions) and SAQ (Short Answer Questions) to help you prepare for your exams.
PART 1: REFLECTION OF LIGHT (SPHERICAL MIRRORS)
Q1. What is the reflection of light?
Ans: The bouncing back of light rays into the same medium after striking a polished surface is called reflection.
Q2. Define the pole of a spherical mirror.
Ans: The geometric center of the reflecting surface of a spherical mirror is called the pole (P).
Q3. What is the center of curvature?
Ans: The center of the hollow glass sphere of which the spherical mirror is a part is called the center of curvature (C).
Q4. Define Principal Focus of a concave mirror.
Ans: The point on the principal axis where light rays parallel to the principal axis converge after reflection is called the Principal Focus (F).
Q5. What is the relationship between radius of curvature (R) and focal length (f)?
Ans: R = 2f (The radius of curvature is twice the focal length).
Q6. Which mirror is known as a converging mirror?
Ans: Concave mirror.
Q7. Which mirror is known as a diverging mirror?
Ans: Convex mirror.
Q8. Write the Mirror Formula.
Ans: 1/v + 1/u = 1/f (Where v = image distance, u = object distance, f = focal length).
Q9. What is the nature of the image formed by a plane mirror?
Ans: Virtual, erect, and of the same size as the object.
Q10. Why do we use convex mirrors as rear-view mirrors in vehicles?
Ans: Because they always give an erect, diminished image and have a wider field of view, allowing the driver to see a large area behind.
Q11. What type of mirror is used by dentists?
Ans: Concave mirror (to see a large image of the teeth).
Q12. Define Magnification (m) of a mirror.
Ans: It is the ratio of the height of the image to the height of the object. Formula: m = -v/u.
Q13. If magnification is negative, what is the nature of the image?
Ans: The image is Real and Inverted.
Q14. If magnification is +1, what does it imply?
Ans: The image is virtual, erect, and of the same size as the object (formed by a plane mirror).
Q15. Where should an object be placed in front of a concave mirror to get a virtual and erect image?
Ans: Between the Pole (P) and the Principal Focus (F).
Q16. Where is the image formed when an object is placed at the center of curvature (C) of a concave mirror?
Ans: At the center of curvature (C). It is real, inverted, and of the same size.
Q17. What happens to a ray of light passing through the center of curvature after reflection?
Ans: It retraces its path (reflects back along the same line).
Q18. Define Principal Axis.
Ans: The straight line passing through the pole and the center of curvature of a spherical mirror.
Q19. What is the sign convention for the object distance (u)?
Ans: Object distance (u) is always taken as negative.
Q20. What is the focal length of a plane mirror?
Ans: Infinity.
Q21. Which mirror is used in solar furnaces?
Ans: Concave mirror (to concentrate sunlight at the focus).
Q22. An object is placed at infinity in front of a convex mirror. Where is the image formed?
Ans: At the focus (F) behind the mirror.
Q23. Why are concave mirrors used in headlights of cars?
Ans: To get a powerful parallel beam of light when the bulb is placed at the focus.
Q24. Can a convex mirror form a real image?
Ans: No, it always forms a virtual image for real objects.
Q25. If the radius of curvature is 20 cm, what is the focal length?
Ans: f = R/2 = 20/2 = 10 cm.
Q26. What is a real image?
Ans: An image that can be obtained on a screen and is formed by the actual intersection of light rays.
Q27. What is a virtual image?
Ans: An image that cannot be obtained on a screen and is formed where light rays appear to meet.
Q28. What is lateral inversion?
Ans: The phenomenon where the left side of an object appears as the right side in the image and vice versa.
Q29. What is the aperture of a mirror?
Ans: The diameter of the reflecting surface of the spherical mirror.
Q30. If 'm' is less than 1 (magnitude), what is the size of the image?
Ans: Diminished (smaller than the object).
PART 2: REFRACTION AND LENSES
Q31. Define Refraction of light.
Ans: The bending of a light ray when it passes obliquely from one transparent medium to another.
Q32. State Snell’s Law of refraction.
Ans: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media. (sin i / sin r = constant).
Q33. What is the Refractive Index?
Ans: It is the ratio of the speed of light in a vacuum (or air) to the speed of light in the medium (n = c/v).
Q34. What is the speed of light in a vacuum?
Ans: 3 × 108 m/s.
Q35. When light travels from a rarer to a denser medium, how does it bend?
Ans: It bends towards the normal.
Q36. When light travels from a denser to a rarer medium, how does it bend?
Ans: It bends away from the normal.
Q37. Which lens is called a converging lens?
Ans: Convex lens.
Q38. Which lens is called a diverging lens?
Ans: Concave lens.
Q39. Write the Lens Formula.
Ans: 1/v - 1/u = 1/f.
Q40. What is the SI unit of Power of a lens?
Ans: Dioptre (D).
Q41. Define 1 Dioptre.
Ans: 1 Dioptre is the power of a lens whose focal length is 1 meter.
Q42. How is Power (P) related to focal length (f)?
Ans: P = 1/f (where f is in meters).
Q43. What is the sign of power for a convex lens?
Ans: Positive (+).
Q44. What is the sign of power for a concave lens?
Ans: Negative (-).
Q45. Define the Optical Center of a lens.
Ans: The central point of a lens through which a ray of light passes without any deviation.
Q46. Where should an object be placed for a convex lens to act as a magnifying glass?
Ans: Between the optical center and the focus.
Q47. If the power of a lens is -2.0 D, what is its focal length and nature?
Ans: f = 1/P = 1/(-2) = -0.5 meters (-50 cm). It is a Concave lens.
Q48. Does the refractive index of a medium depend on the color of light?
Ans: Yes, the refractive index is highest for violet light and lowest for red light.
Q49. Why does a pencil appear bent in water?
Ans: Due to the refraction of light as it moves from water (denser) to air (rarer).
Q50. What is the magnification formula for a lens?
Ans: m = v/u (or m = height of image / height of object).
Q51. A convex lens forms a real, inverted image of the same size. Where is the object placed?
Ans: At 2F (twice the focal length).
Q52. What is absolute refractive index?
Ans: The refractive index of a medium with respect to a vacuum.
Q53. Which substance has the highest refractive index?
Ans: Diamond (2.42).
Q54. Why does light not bend when it falls normally (perpendicularly) on a surface?
Ans: Because the angle of incidence is 0, so the angle of refraction is also 0.
Q55. Why is a convex lens thicker at the middle?
Ans: Structurally, a convex lens is thick at the center and thin at the edges to converge light.
Q56. What happens to the power of a combination of lenses?
Ans: The total power is the algebraic sum of individual powers (P = P1 + P2 + ...).
Q57. A concave lens always forms what kind of image?
Ans: Virtual, erect, and diminished.
Q58. Define relative refractive index.
Ans: The ratio of the speed of light in medium 1 to the speed of light in medium 2.
Q59. Where is the image formed if an object is at infinity for a convex lens?
Ans: At the focus (F2).
Q60. Can a lens have two focal lengths?
Ans: Yes, a lens has two principal foci (F1 and F2) because light can pass from both sides.
PART 3: THE HUMAN EYE AND COLORFUL WORLD
Q61. Which part of the human eye acts as a screen?
Ans: Retina.
Q62. What is the function of the pupil?
Ans: It regulates and controls the amount of light entering the eye.
Q63. What controls the size of the pupil?
Ans: Iris.
Q64. What is the Power of Accommodation?
Ans: The ability of the eye lens to adjust its focal length to see objects at varying distances clearly.
Q65. What is the near point of a normal human eye?
Ans: 25 cm.
Q66. What is the far point of a normal human eye?
Ans: Infinity.
Q67. What is Myopia?
Ans: Near-sightedness. A person can see nearby objects clearly but cannot see distant objects distinctly.
Q68. How is Myopia corrected?
Ans: By using a Concave lens of suitable power.
Q69. What causes Myopia?
Ans: Excessive curvature of the eye lens or elongation of the eyeball.
Q70. What is Hypermetropia?
Ans: Far-sightedness. A person can see distant objects clearly but cannot see nearby objects distinctly.
Q71. How is Hypermetropia corrected?
Ans: By using a Convex lens of suitable power.
Q72. What is Presbyopia?
Ans: An age-related defect where the power of accommodation decreases, making it difficult to see nearby objects.
Q73. How is Presbyopia corrected?
Ans: Using Bifocal lenses (Concave upper part, Convex lower part).
Q74. What is the function of ciliary muscles?
Ans: They modify the curvature of the eye lens to change its focal length.
Q75. What are rods and cones?
Ans: Rods are light-sensitive cells (dim light), and cones are color-sensitive cells present in the retina.
Q76. Why do we have two eyes instead of one?
Ans: To have a wider field of view and depth perception (3D vision).
Q77. What is a Prism?
Ans: A homogeneous transparent medium bounded by two plane surfaces inclined at an angle.
Q78. What is the Angle of Deviation?
Ans: The angle between the incident ray and the emergent ray in a prism.
Q79. Define Dispersion of light.
Ans: The splitting of white light into its constituent seven colors.
Q80. What is the Spectrum?
Ans: The band of seven colors obtained due to the dispersion of white light (VIBGYOR).
Q81. Which color deviates the most in a prism?
Ans: Violet.
Q82. Which color deviates the least in a prism?
Ans: Red.
Q83. Who discovered that sunlight consists of seven colors?
Ans: Isaac Newton.
Q84. What causes a Rainbow?
Ans: Dispersion, refraction, and internal reflection of sunlight by tiny water droplets in the atmosphere.
Q85. What is Atmospheric Refraction?
Ans: The refraction of light caused by the earth's atmosphere due to varying optical densities of air layers.
Q86. Why do stars twinkle?
Ans: Due to atmospheric refraction, the apparent position of the star keeps changing slightly, and the amount of light entering the eye flickers.
Q87. Why don't planets twinkle?
Ans: Planets are closer and appear as extended sources of light. The variation in light from different points cancels out.
Q88. Why does the sun appear slightly oval?
Ans: Due to atmospheric refraction.
Q89. What is Scattering of light?
Ans: The phenomenon where light is deflected in all directions by particles (dust, molecules) present in the atmosphere.
Q90. What is the Tyndall Effect?
Ans: The scattering of light by colloidal particles in a medium, making the path of the light beam visible.
Q91. Why is the sky blue?
Ans: The fine particles in the atmosphere scatter blue light (shorter wavelength) more strongly than red light.
Q92. Why are danger signals red?
Ans: Red light has the longest wavelength and is scattered the least by fog or smoke, so it can be seen from a long distance.
Q93. Why does the sky appear dark to an astronaut?
Ans: Because there is no atmosphere in space to scatter light.
Q94. What is a Cataract?
Ans: A condition where the eye lens becomes milky and cloudy, leading to partial or complete loss of vision. It is corrected by surgery.
Q95. What is the blind spot?
Ans: The junction of the optic nerve and the retina where there are no light-sensitive cells.
Q96. What is the recombination of the spectrum?
Ans: If an inverted prism is placed after a prism dispersing light, the seven colors recombine to form white light.
Q97. What is Persistence of Vision?
Ans: The image remains on the retina for about 1/16th of a second even after the object is removed.
Q98. In which defect is the image formed behind the retina?
Ans: Hypermetropia.
Q99. In which defect is the image formed in front of the retina?
Ans: Myopia.
Q100. Why do stars appear higher than they actually are?
Ans: Due to atmospheric refraction, light from stars bends towards the normal as it enters the earth's atmosphere.
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