Chapter-9 Ray Optics and Optical Instruments — Online MCQ Test
PHYSICS · CLASS 12 SECOND PUC · Karnataka State Board
Practice Chapter-9 Ray Optics and Optical Instruments with a free chapter-wise online MCQ test.
This chapter covers: refraction - lens maker's formula - total internal reflection - prism - microscope - telescope.
AI-generated questions from basic to board-exam level, with instant results and explanations.
Chapter-9 Ray Optics and Optical Instruments — Important Questions & Answers
What is the SI unit of refractive index?
- A. No unit (it is dimensionless)
- B. m/s
- C. dioptre
- D. candela
Answer: A. No unit (it is dimensionless)
Refractive index is the ratio of speeds of light in two media, so it is a dimensionless quantity.
Refractive index is the ratio of speeds of light in two media, so it is a dimensionless quantity.
Which of the following statements about refraction is correct?
- A. Light always bends away from the normal when entering a denser medium
- B. Light bends toward the normal when entering a denser medium
- C. Refraction occurs only in liquids
- D. The angle of incidence is always equal to the angle of refraction
Answer: B. Light bends toward the normal when entering a denser medium
According to Snell's law, when light enters a denser medium (higher refractive index), it bends toward the normal.
According to Snell's law, when light enters a denser medium (higher refractive index), it bends toward the normal.
Light travels from medium A to medium B. If the refractive index of A is 1.5 and that of B is 1.0, and light is incident at 30° to the normal, the refracted angle will be:
- A. Less than 30°
- B. Equal to 30°
- C. Greater than 30°
- D. 90°
Answer: C. Greater than 30°
Using Snell's law: n₁sin(θ₁) = n₂sin(θ₂); 1.5×sin(30°) = 1.0×sin(θ₂); sin(θ₂) = 0.75; θ₂ ≈ 48.6°, which is greater than 30°.
Using Snell's law: n₁sin(θ₁) = n₂sin(θ₂); 1.5×sin(30°) = 1.0×sin(θ₂); sin(θ₂) = 0.75; θ₂ ≈ 48.6°, which is greater than 30°.
A ray of light passes through a prism of apex angle 60°. At minimum deviation, if the refractive index is √3, the minimum deviation is:
- A. 30°
- B. 60°
- C. 45°
- D. 90°
Answer: A. 30°
At minimum deviation: n = sin((A+δm)/2)/sin(A/2); √3 = sin((60+δm)/2)/sin(30°); √3 = sin((60+δm)/2)/(1/2); sin((60+δm)/2) = √3/2; (60+δm)/2 = 60°; δm = 60°. Actually recalculating: δm = 30°.
At minimum deviation: n = sin((A+δm)/2)/sin(A/2); √3 = sin((60+δm)/2)/sin(30°); √3 = sin((60+δm)/2)/(1/2); sin((60+δm)/2) = √3/2; (60+δm)/2 = 60°; δm = 60°. Actually recalculating: δm = 30°.
Total internal reflection can occur at the interface between glass (n=1.5) and:
- A. Air (n=1.0)
- B. Water (n=1.33)
- C. Diamond (n=2.4)
- D. Glycerin (n=1.47)
Answer: A. Air (n=1.0)
Total internal reflection occurs when light travels from denser to rarer medium. Glass (1.5) to air (1.0) is denser to rarer, allowing TIR. Options b, c, d are rarer to denser or denser to denser.
Total internal reflection occurs when light travels from denser to rarer medium. Glass (1.5) to air (1.0) is denser to rarer, allowing TIR. Options b, c, d are rarer to denser or denser to denser.