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Chapter 9: Ray Optics

NCERT Solutions for CBSE Class 10 Physics — 73 solved questions with detailed explanations.

73

Questions

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Topics

Solved Questions

Q1. The focal length of a concave mirror of radius of curvature 20 cm is:

20 cm
10 cm
40 cm
5 cm

Difficulty: Easy · Topic: Mirror Formula

Solution

f = R/2 = 20/2 = 10 cm.

Q2. The refractive index of a medium where the speed of light is 2 × 10⁸ m/s is:

1.5
2.0
0.67
3.0

Difficulty: Easy · Topic: Refraction

Solution

n = c/v = 3×10⁸/2×10⁸ = 1.5.

Q3. Total internal reflection occurs when light travels from:

Rarer to denser medium
Denser to rarer medium
Any medium to vacuum
Vacuum to any medium

Difficulty: Easy · Topic: TIR

Solution

TIR requires light going from denser (higher n) to rarer (lower n) medium at angle > critical angle.

Q4. A concave mirror (R=20 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q5. A concave mirror (R=24 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q6. A concave mirror (R=28 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q7. A concave mirror (R=32 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q8. A concave mirror (R=36 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q9. A concave mirror (R=40 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q10. A concave mirror (R=44 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q11. A concave mirror (R=48 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q12. A concave mirror (R=52 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q13. A concave mirror (R=56 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q14. A concave mirror (R=60 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q15. A concave mirror (R=64 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q16. A concave mirror (R=68 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q17. A concave mirror (R=72 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q18. A concave mirror (R=76 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q19. A concave mirror (R=80 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q20. A concave mirror (R=84 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q21. A concave mirror (R=88 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q22. A concave mirror (R=92 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q23. A concave mirror (R=96 cm) has focal length:

Difficulty: Easy · Topic: Mirror

Solution

f = R/2.

Q24. Mirror R=4cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=2 cm.

Q25. Mirror R=6cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=3 cm.

Q26. Mirror R=8cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=4 cm.

Q27. Mirror R=10cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=5 cm.

Q28. Mirror R=12cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=6 cm.

Q29. Mirror R=14cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=7 cm.

Q30. Mirror R=16cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=8 cm.

Q31. Mirror R=18cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=9 cm.

Q32. Mirror R=20cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=10 cm.

Q33. Mirror R=22cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=11 cm.

Q34. Mirror R=24cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=12 cm.

Q35. Mirror R=26cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=13 cm.

Q36. Mirror R=28cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=14 cm.

Q37. Mirror R=30cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=15 cm.

Q38. Mirror R=32cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=16 cm.

Q39. Mirror R=34cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=17 cm.

Q40. Mirror R=36cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=18 cm.

Q41. Mirror R=38cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=19 cm.

Q42. Mirror R=40cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=20 cm.

Q43. Mirror R=42cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=21 cm.

Q44. Mirror R=44cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=22 cm.

Q45. Mirror R=46cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=23 cm.

Q46. Mirror R=48cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=24 cm.

Q47. Mirror R=50cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=25 cm.

Q48. Mirror R=52cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=26 cm.

Q49. Mirror R=54cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=27 cm.

Q50. Mirror R=56cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=28 cm.

Q51. Mirror R=58cm. Focal length:

Difficulty: Easy · Topic: Mirror

Solution

f=R/2=29 cm.

Q52. Speed of light in medium is 1.0×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/1.0=3.0.

Q53. Speed of light in medium is 1.2×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/1.2=2.5.

Q54. Speed of light in medium is 1.5×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/1.5=2.0.

Q55. Speed of light in medium is 1.8×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/1.8=1.67.

Q56. Speed of light in medium is 2.0×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/2.0=1.5.

Q57. Speed of light in medium is 2.25×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/2.25=1.33.

Q58. Speed of light in medium is 2.5×10⁸ m/s. Refractive index:

Difficulty: Easy · Topic: Refraction

Solution

n=c/v=3/2.5=1.2.

Q59. An equiconvex lens of focal length f is cut into two equal halves along the principal axis. The focal length of each half is:

f
2f
f/2
3f/2

Difficulty: Medium · Topic: Lens Cutting

Solution

Cutting along the principal axis gives a plano-convex lens. Using lensmaker's equation, focal length doubles to 2f.

Q60. For a mirror with f=-10 cm and u=-20 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/-10 - 1/(-20). v = -20.0 cm.

Q61. For a mirror with f=-15 cm and u=-30 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/-15 - 1/(-30). v = -30.0 cm.

Q62. For a mirror with f=-20 cm and u=-40 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/-20 - 1/(-40). v = -40.0 cm.

Q63. For a mirror with f=10 cm and u=-20 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/10 - 1/(-20). v = 6.67 cm.

Q64. For a mirror with f=15 cm and u=-30 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/15 - 1/(-30). v = 10.0 cm.

Q65. For a mirror with f=20 cm and u=-30 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/20 - 1/(-30). v = 12.0 cm.

Q66. For a mirror with f=-10 cm and u=-15 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/-10 - 1/(-15). v = -30.0 cm.

Q67. For a mirror with f=-20 cm and u=-30 cm, the image distance v is:

Difficulty: Medium · Topic: Mirror Formula

Solution

1/v = 1/f - 1/u = 1/-20 - 1/(-30). v = -60.0 cm.

Q68. A lens of focal length 20 cm with object at -30 cm gives image at:

Difficulty: Medium · Topic: Lens Formula

Solution

1/v - 1/u = 1/f. v = uf/(u+f) = -30×20/(-30+20) = 12.0 cm.

Q69. A lens of focal length 10 cm with object at -15 cm gives image at:

Difficulty: Medium · Topic: Lens Formula

Solution

1/v - 1/u = 1/f. v = uf/(u+f) = -15×10/(-15+10) = 6.0 cm.

Q70. A lens of focal length 15 cm with object at -20 cm gives image at:

Difficulty: Medium · Topic: Lens Formula

Solution

1/v - 1/u = 1/f. v = uf/(u+f) = -20×15/(-20+15) = 8.57 cm.

Q71. A lens of focal length -10 cm with object at -5 cm gives image at:

Difficulty: Medium · Topic: Lens Formula

Solution

1/v - 1/u = 1/f. v = uf/(u+f) = -5×-10/(-5+-10) = 10.0 cm.

Q72. A lens of focal length 20 cm with object at -40 cm gives image at:

Difficulty: Medium · Topic: Lens Formula

Solution

1/v - 1/u = 1/f. v = uf/(u+f) = -40×20/(-40+20) = 13.33 cm.

Q73. A lens of focal length -20 cm with object at -30 cm gives image at:

Difficulty: Medium · Topic: Lens Formula

Solution

1/v - 1/u = 1/f. v = uf/(u+f) = -30×-20/(-30+-20) = -60.0 cm.

Other Chapters in Physics

Ch 1: Electric Charges & Fields Ch 2: Electrostatic Potential Ch 3: Current Electricity Ch 4: Moving Charges & Magnetism Ch 5: Magnetism & Matter Ch 6: Electromagnetic Induction Ch 7: Alternating Current Ch 8: Electromagnetic Waves Ch 10: Wave Optics Ch 11: Dual Nature of Radiation Ch 12: Atoms Ch 13: Nuclei Ch 14: Semiconductor Electronics

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