Practice Questions for Science Class 10th "Reflection and Refraction"

Multiple Choice Questions (MCQs):

1. B) Angle of incidence - The angle between the incident ray and the normal at the point of incidence.
2. C) Law of reflection - States that the angle of incidence equals the angle of reflection.
3. B) It bends away from the normal - When light moves from a denser to a rarer medium.
4. B) Refraction - The bending of light as it passes from one medium to another.
5. B) Concave mirror - A mirror that curves inward.
6. B) Virtual and erect - The characteristics of an image formed by a plane mirror.
7. A) Speed of light in vacuum/speed of light in the medium - The formula for refractive index.
8. C) Dispersion - The splitting of white light into its spectrum.
9. B) Convex lens - Converges light rays to a focal point.
10. A) Half the radius of curvature - For spherical mirrors, the focal length (f) is half the radius of curvature (R), f = R/2.
11. A) Dioptre - The unit for measuring the power of a lens.
12. B) Its wavelength decreases - When light enters a denser medium like glass, its speed and wavelength decrease, but frequency remains constant.
13. B) Convex - Provides a wider field of view, making it ideal for rear-view mirrors.
14. B) Focus - The point where parallel rays of light converge or appear to diverge after reflection/refraction.
15. A) Light travels from a denser to a rarer medium at an angle greater than the critical angle - This leads to total internal reflection.
16. B) Convex - Used in simple microscopes to magnify images.
17. A) 2 × 10^8 m/s - Speed of light in medium = speed in vacuum/refractive index = 3 × 10^8 m/s / 1.5.
18. B) Refraction - Due to varying densities in Earth's atmosphere, light from stars refracts differently, causing twinkling.
19. C) Emerges undeviated - Light passing through the optical centre of a lens does not deviate.
20. C) Diffraction - The bending of light around obstacles or through narrow slits.

Short Answer Questions:

21. Refractive Index: The ratio of the speed of light in vacuum to the speed of light in a medium.
22. Principal Focus of Concave Mirror: The point where parallel rays of light converge after reflection.
23. Pencil Appearing Bent: Due to refraction, light from the pencil bends at the water-air interface, creating a virtual image that looks bent.
24. Real vs. Virtual Images:

• Real: Can be projected onto a screen, formed by actual light rays converging.
• Virtual: Cannot be projected, formed by apparent divergence of light rays.

25. Thickness and Focal Length: Thicker lenses have shorter focal lengths because they bend light more.
26. Total Internal Reflection: When light traveling in a denser medium hits the interface at an angle greater than the critical angle, it reflects entirely back into the denser medium.
27. Power of a Lens: Power = 1/focal length in meters (in dioptres). Shorter focal length means higher power.
28. Blue Sky: Due to Rayleigh scattering where shorter blue light is scattered more by atmospheric particles.
29. Critical Angle: The angle of incidence at which the refracted angle becomes 90°, beyond which total internal reflection occurs.
30. Demonstrating Reflection Laws: Use a plane mirror, light source, and protractor to measure angles; verify angle of incidence equals angle of reflection.
31. Light from Glass to Air: Light bends away from the normal if it's at an angle less than the critical angle; if greater, it reflects back.
32. Dispersion: The separation of white light into its constituent colors due to different refractive indices for different wavelengths.
33. Curvature and Focal Length: More curved mirrors have shorter focal lengths because they converge light rays more sharply.
34. Convex Mirrors for Rear-View: They provide a wider field of view, making it easier to see traffic behind.
35. Sign Convention in Optics: Helps determine image type, position, and nature; distances to the left of the mirror/lens are negative, right positive, etc.
36. Image by Convex Lens:

• Object at infinity: Image at focus, real, inverted, diminished.
• Object beyond 2F: Image between F and 2F, real, inverted, diminished.
• Object at 2F: Image at 2F, real, inverted, same size.
• Object between F and 2F: Image beyond 2F, real, inverted, magnified.
• Object within F: Virtual, erect, magnified.

37. Optical Centre: The central point of a lens through which light rays pass without deviation.
38. Uses of Concave Mirrors:

• Dental mirrors, solar heaters, reflectors in torches, make-up mirrors.

39. Diamond Sparkle: Due to total internal reflection and dispersion, light is trapped and reflected multiple times, enhancing brightness and color.
40. Lenses and Vision Correction:

• Convex: For farsightedness, converge light to focus on the retina.
• Concave: For nearsightedness, diverge light to extend focal length.

Long Answer Questions:

41. Laws of Reflection:

• First Law: The incident ray, the normal, and the reflected ray all lie in the same plane.
• Second Law: The angle of incidence equals the angle of reflection. [Include a diagram showing this.]

42. Snell's Law:

• n₁sin(θ₁) = n₂sin(θ₂), where n is the refractive index, θ is the angle. Relates to refractive index by showing how light bends at different angles based on medium properties. [Include a diagram for refraction.]

43. Image Formation by Mirrors:

• Concave: Can form real or virtual images depending on object position; rays converge or appear to diverge. [Include ray diagrams for different positions.]
• Convex: Always forms virtual, erect, diminished images; rays diverge. [Include ray diagram.]

44. Applications of Total Internal Reflection:

• Optical fibers for communication, prisms in binoculars, total reflection prisms in photography, and endoscopes in medicine.

45. Human Eye:

• Light is refracted by the cornea, then by the lens which can change shape to focus light on the retina. Reflection off the retina forms an inverted image processed by the brain. [Include a diagram of the eye.]

46. Real vs. Virtual Images Comparison:

• Real: Formed by converging rays, can be captured on screen, always inverted (except for magnifying glass at close range).
• Virtual: Formed by diverging rays or appearance of divergence, cannot be captured on screen, always erect.

47. Lenses and Light:

• Convex: Converges light, forms real or virtual images based on object position.
• Concave: Diverges light, always forms virtual, erect images.

48. Dispersion and Rainbow:

• Dispersion splits light due to varying refractive indices for different colors. Rainbows occur when light is refracted, reflected, and dispersed in water droplets.

49. Power of Lens:

• Power = 1/f (where f is in meters). A higher power means a shorter focal length, thus stronger bending of light.

50. Focal Length Experiment:

• Use the lens to form a sharp image of a distant object on a screen. Distance from lens to screen is the focal length. [Explain setup with diagram.]

51. Refractive Index and Optical Instruments:

• Higher refractive index materials can bend light more, making for compact designs but also introducing more aberrations.

52. Lenses in Cameras/Microscopes:

• Cameras: Convex lenses focus light to form images on film/sensor.
• Microscopes: Use combinations of lenses to magnify and focus on tiny objects.

53. Critical Angle in Fiber Optics:

• Light must enter at an angle less than the critical angle to be totally internally reflected along the fiber, enabling light transmission with minimal loss.

54. Atmospheric Refraction and Stars:

• Light from stars refracts through varying air densities, causing stars to twinkle or appear to shift position.

55. Human Eye Image Formation:

• The lens changes shape (accommodation) to focus light from near or far objects onto the retina, where it's converted to electrical signals.

56. Conditions for Total Internal Reflection:

• Light must travel from denser to rarer medium, and the angle of incidence must exceed the critical angle.

57. Mirrors vs. Lenses:

• Advantages of Mirrors: No chromatic aberration, can handle high light intensity.
• Disadvantages: Bulky for large apertures.
• Advantages of Lenses: Compact, easy to combine for systems.
• Disadvantages: Chromatic aberration, limited by material properties.

58. Chromatic Aberration:

• Different wavelengths of light bend at different angles, causing color fringes. Minimized with achromatic lenses (combining lenses of different materials).

59. Prism and Dispersion:

• Prisms have a triangular shape where light enters, refract

61. Angle of Reflection: If the angle of incidence is 30°, the angle of reflection will also be 30° because of the law of reflection.
62. Experiment for Refraction in Water:

• Place a straight object like a pencil in a glass of water at an angle. Observe from the side; the pencil will appear bent due to refraction.

63. Speed of Light in Medium:

• Speed of light in medium = Speed of light in vacuum / Refractive index = 3 × 10^8 m/s / 1.33 ≈ 2.26 × 10^8 m/s.

64. Demonstrating Dispersion at Home:

• Shine a flashlight through a prism or a glass of water with a narrow slit. The light will disperse into a spectrum of colors on a white screen or wall.

65. Power of a Lens:

• Power = 1/f (in meters), f = 20 cm = 0.2 m, so Power = 1/0.2 = 5 Dioptres.

66. Using Concave Mirror to Light Paper:

• Place the paper at the focal point of a concave mirror, aim sunlight or a strong light source at the mirror to concentrate light onto the paper, causing it to burn.

67. Measuring Refractive Index with Laser:

• Use a laser to trace light path through a glass block, measure the angles of incidence and refraction, use Snell's law to calculate the refractive index.

68. Periscope Design:

• Use two plane mirrors at 45° angles to each other in a tube. Light reflects off one mirror to the next, allowing you to see over obstacles.

69. Critical Angle and Total Internal Reflection:

• If the angle of incidence is 43°, which is greater than the critical angle of 42°, the light will be totally internally reflected back into the glass.

70. Starting Fire with Convex Lens:

• Focus sunlight with a convex lens onto a small piece of paper or tinder at the focal point. The concentrated light will heat up and ignite the material.

Critical Thinking Questions:

71. Reflection and Refraction in Technology:

• Used in VR/AR headsets for image projection, optical data storage, solar concentrators, and advanced imaging systems in medicine.

72. High Refractive Index Materials:

• Allow for smaller, lighter optics but can introduce more chromatic and spherical aberrations, requiring complex corrections.

73. Astronomy and Optics:

• Understanding light's behavior through different media helps in designing telescopes, correcting for atmospheric distortion, and analyzing starlight spectra.

74. Environmental Considerations in Lens/Mirror Manufacturing:

• Involves resource use, chemical waste, energy consumption, and the lifecycle of products, pushing for sustainable materials and recycling.

75. Optics and Energy Efficiency:

• Efficient light distribution with lenses or reflective surfaces, reducing energy waste in lighting systems like LED technology.

76. Ethics of Optical Surveillance:

• Privacy concerns, potential for misuse, need for transparency and consent, and the balance between security and individual rights.

77. Optics in Medicine:

• Endoscopy, laser surgery, non-invasive diagnostics like OCT (Optical Coherence Tomography), and advanced microscopy techniques.

78. Reflection and Refraction in Daily Life:

• Mirrors for self-viewing, lenses in glasses, rainbows, mirages, the blue sky, and the use of prisms in optical instruments.

79. Optical Systems for Underwater:

• Challenges include water's high refractive index causing distortion, pressure effects on equipment, and maintaining clarity in turbid conditions.

80. Light Pollution Reduction:

• Using optics to direct light only where needed (light shields, directional lighting), promoting low-glare LED technology, and educating on light use to minimize sky glow.