Class 10 Physics: Light - Reflection & Refraction (Q&A)
Q1. Define principal axis of a spherical mirror.
Ans: The straight line passing through the pole and the centre of curvature is called the principal axis of the mirror.
Q2. Which mirror is convergent, concave or convex?
Ans: Concave mirror.
Q3. Can a convex mirror form a magnified image?
Ans: No.
Q4. When does a concave mirror form a virtual image?
Ans: When the object lies between the pole and focus of the mirror.
Q5. What is the relation between f and r of a spherical mirror?
Ans: f = r/2
Q6. Which of the following does not change when light goes from one medium to another: frequency, wavelength, speed, or intensity?
Ans: Frequency
Q7. What is the absolute refractive index of vacuum?
Ans: 1
Q8. For which medium is refractive index (i) minimum (ii) maximum?
Ans: (i) Vacuum (=1) (ii) Diamond (=2.42)
Q9. Does critical angle depend on the colour of light?
Ans: Yes, as refractive index varies with colour.
Q10. What do you mean by refraction of light?
Ans: Bending of light when it passes from one medium to another.
Q11. What is the basic cause of refraction of light?
Ans: Different speeds of light in different media.
Q12. Where is the image formed when an object is placed at the focus of a concave lens?
Ans: Between focus and optical centre on the same side of the lens.
Q13. Define power of a lens.
Ans: Reciprocal of focal length in metres.
Q14. How can a convex lens behave like a diverging lens?
Ans: When placed in a medium with a higher refractive index than the lens.
Q15. What is deviation produced in a prism?
Ans: Angle between incident and emergent ray.
Q16. What is meant by dispersion of light?
Ans: Splitting of white light into its constituent colours.
Q17. Which colour deviates (i) most (ii) least in a prism?
Ans: (i) Violet (ii) Red
Q18. Is dispersion of white light in vacuum possible?
Ans: No.
Q19. Does a beam of light give spectrum in air-filled prism?
Ans: No, all colours travel at the same speed in air.
Q20. Which colour has (i) maximum (ii) minimum velocity in glass?
Ans: (i) Red (ii) Violet
Q21. What is the essential condition for observing a rainbow?
Ans: The sun must be behind the observer after rain.
Q22. Can a short-sighted person read books without glasses?
Ans: Yes.
Q23. What lens corrects myopia?
Ans: Concave lens.
Q24. What is the least distance of distinct vision?
Ans: 25 cm.
Q25. What is the far point of a normal eye?
Ans: Infinity.
Q26. How many colours mix to produce white light?
Ans: Seven.
Q27. What is the image position when object is at 2f in convex lens?
Ans: At 2f on the other side, real, inverted, same size.
Q28. What is a convex lens?
Ans: A lens thicker at the centre than edges.
Q29. What is a spectrum?
Ans: Band of colours formed due to dispersion.
Q30. What is a lens?
Ans: Transparent object with two refracting surfaces.
Q31. What is a concave lens?
Ans: Lens thinner at the centre and thicker at edges.
Q32. What is linear magnification?
Ans: Ratio of height of image to height of object.
Q33. How does green cloth appear in red light?
Ans: Black.
Q34. What colour is used in danger signals?
Ans: Red.
Q35. What type of reflection is used in torches?
Ans: Concave mirror reflection.
Q36. What does Refractive Index 2.41 mean?
Ans: Light travels 2.41 times faster in air than in diamond.
Q37. What factors affect lateral shift?
Ans: Thickness of slab, angle of incidence, refractive index.
Q38. What is the angle of refraction if angle of incidence is 90°?
Ans: Ray travels along the boundary, no refraction.
Q39. Why can’t a normal eye see objects closer than 25 cm clearly?
Ans: Eye lens cannot accommodate enough.
Q40. Is dispersion possible without refraction?
Ans: No, dispersion occurs due to different speeds after refraction.
Q41. Which ray has the highest frequency?
Ans: Gamma ray.
Q42. What would be the sky colour without atmosphere?
Ans: Black.
Q43. What is centre of curvature of a lens?
Ans: Centre of the sphere of which lens is a part.
Q44. What is the principal axis of a convex lens?
Ans: Line joining both centres of curvature.
Q45. What is radius of curvature?
Ans: Radius of the sphere from which lens is made.
Q46. What is focus of a convex lens?
Ans: Point where parallel rays converge after refraction.
Q47. What is optical centre?
Ans: Point on principal axis where light passes undeviated.
Q48. Which mirror is used for shaving and why?
Ans: Concave mirror; it gives magnified erect image when close to face.
Q49. What is myopia?
Ans: Short-sightedness; far objects are blurry.
Q50. Why do stars twinkle?
Ans: Atmospheric refraction due to temperature and density changes.
Q51. Which type of image can be cast on a screen?
Ans: Real image.
Q52. Why is glycerine not visible in a glass bottle?
Ans: Because it has nearly the same refractive index as glass.
Ans: The process by which light is redirected in different directions when it strikes small particles in the atmosphere.
Q54. Why is the sky blue?
Ans: Because blue light is scattered the most by the atmosphere due to its shorter wavelength.
Q55. Why does the sky appear reddish at sunrise and sunset?
Ans: At sunrise and sunset, sunlight travels a longer path through the atmosphere. Most of the blue and shorter wavelengths are scattered away, leaving red and orange hues.
Q56. Why do stars appear to twinkle?
Ans: Due to atmospheric refraction and scattering caused by turbulence in air layers.
Q57. Why do planets not twinkle?
Ans: Planets are closer and appear as extended sources, so variations in light cancel out, preventing twinkling.
Q58. What would happen to the colour of the sky if there were no atmosphere?
Ans: The sky would appear black because there would be no scattering of sunlight.
Q59. Name one real-life application of scattering.
Ans: Tyndall effect observed in colloidal solutions or headlights appearing bluish in fog.
Ans: The straight line passing through the pole and the centre of curvature is called the principal axis of the mirror.
Q2. Which mirror is convergent, concave or convex?
Ans: Concave mirror.
Q3. Can a convex mirror form a magnified image?
Ans: No.
Q4. When does a concave mirror form a virtual image?
Ans: When the object lies between the pole and focus of the mirror.
Q5. What is the relation between f and r of a spherical mirror?
Ans: f = r/2
Q6. Which of the following does not change when light goes from one medium to another: frequency, wavelength, speed, or intensity?
Ans: Frequency
Q7. What is the absolute refractive index of vacuum?
Ans: 1
Q8. For which medium is refractive index (i) minimum (ii) maximum?
Ans: (i) Vacuum (=1) (ii) Diamond (=2.42)
Q9. Does critical angle depend on the colour of light?
Ans: Yes, as refractive index varies with colour.
Q10. What do you mean by refraction of light?
Ans: Bending of light when it passes from one medium to another.
Q11. What is the basic cause of refraction of light?
Ans: Different speeds of light in different media.
Q12. Where is the image formed when an object is placed at the focus of a concave lens?
Ans: Between focus and optical centre on the same side of the lens.
Q13. Define power of a lens.
Ans: Reciprocal of focal length in metres.
Q14. How can a convex lens behave like a diverging lens?
Ans: When placed in a medium with a higher refractive index than the lens.
Q15. What is deviation produced in a prism?
Ans: Angle between incident and emergent ray.
Q16. What is meant by dispersion of light?
Ans: Splitting of white light into its constituent colours.
Q17. Which colour deviates (i) most (ii) least in a prism?
Ans: (i) Violet (ii) Red
Q18. Is dispersion of white light in vacuum possible?
Ans: No.
Q19. Does a beam of light give spectrum in air-filled prism?
Ans: No, all colours travel at the same speed in air.
Q20. Which colour has (i) maximum (ii) minimum velocity in glass?
Ans: (i) Red (ii) Violet
Q21. What is the essential condition for observing a rainbow?
Ans: The sun must be behind the observer after rain.
Q22. Can a short-sighted person read books without glasses?
Ans: Yes.
Q23. What lens corrects myopia?
Ans: Concave lens.
Q24. What is the least distance of distinct vision?
Ans: 25 cm.
Q25. What is the far point of a normal eye?
Ans: Infinity.
Q26. How many colours mix to produce white light?
Ans: Seven.
Q27. What is the image position when object is at 2f in convex lens?
Ans: At 2f on the other side, real, inverted, same size.
Q28. What is a convex lens?
Ans: A lens thicker at the centre than edges.
Q29. What is a spectrum?
Ans: Band of colours formed due to dispersion.
Q30. What is a lens?
Ans: Transparent object with two refracting surfaces.
Q31. What is a concave lens?
Ans: Lens thinner at the centre and thicker at edges.
Q32. What is linear magnification?
Ans: Ratio of height of image to height of object.
Q33. How does green cloth appear in red light?
Ans: Black.
Q34. What colour is used in danger signals?
Ans: Red.
Q35. What type of reflection is used in torches?
Ans: Concave mirror reflection.
Q36. What does Refractive Index 2.41 mean?
Ans: Light travels 2.41 times faster in air than in diamond.
Q37. What factors affect lateral shift?
Ans: Thickness of slab, angle of incidence, refractive index.
Q38. What is the angle of refraction if angle of incidence is 90°?
Ans: Ray travels along the boundary, no refraction.
Q39. Why can’t a normal eye see objects closer than 25 cm clearly?
Ans: Eye lens cannot accommodate enough.
Q40. Is dispersion possible without refraction?
Ans: No, dispersion occurs due to different speeds after refraction.
Q41. Which ray has the highest frequency?
Ans: Gamma ray.
Q42. What would be the sky colour without atmosphere?
Ans: Black.
Q43. What is centre of curvature of a lens?
Ans: Centre of the sphere of which lens is a part.
Q44. What is the principal axis of a convex lens?
Ans: Line joining both centres of curvature.
Q45. What is radius of curvature?
Ans: Radius of the sphere from which lens is made.
Q46. What is focus of a convex lens?
Ans: Point where parallel rays converge after refraction.
Q47. What is optical centre?
Ans: Point on principal axis where light passes undeviated.
Q48. Which mirror is used for shaving and why?
Ans: Concave mirror; it gives magnified erect image when close to face.
Q49. What is myopia?
Ans: Short-sightedness; far objects are blurry.
Q50. Why do stars twinkle?
Ans: Atmospheric refraction due to temperature and density changes.
Q51. Which type of image can be cast on a screen?
Ans: Real image.
Q52. Why is glycerine not visible in a glass bottle?
Ans: Because it has nearly the same refractive index as glass.
Scattering of Light – Important Points
Q53. What is scattering of light?Ans: The process by which light is redirected in different directions when it strikes small particles in the atmosphere.
Q54. Why is the sky blue?
Ans: Because blue light is scattered the most by the atmosphere due to its shorter wavelength.
Q55. Why does the sky appear reddish at sunrise and sunset?
Ans: At sunrise and sunset, sunlight travels a longer path through the atmosphere. Most of the blue and shorter wavelengths are scattered away, leaving red and orange hues.
Q56. Why do stars appear to twinkle?
Ans: Due to atmospheric refraction and scattering caused by turbulence in air layers.
Q57. Why do planets not twinkle?
Ans: Planets are closer and appear as extended sources, so variations in light cancel out, preventing twinkling.
Q58. What would happen to the colour of the sky if there were no atmosphere?
Ans: The sky would appear black because there would be no scattering of sunlight.
Q59. Name one real-life application of scattering.
Ans: Tyndall effect observed in colloidal solutions or headlights appearing bluish in fog.
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