Chapter Exam

Chapter-9 Ray Optics and Optical Instruments — Online MCQ Test

Q: What is the SI unit of refractive index?

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.

Q: 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:

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°.

Q: 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:

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°.

Q: Total internal reflection can occur at the interface between glass (n=1.5) and:

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.

PHYSICS · Grade 12 · CBSE(NCERT)

Practice Chapter-9 Ray Optics and Optical Instruments with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 PHYSICS. 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.

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Chapter-9 Ray Optics and Optical Instruments — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 PHYSICS — Chapter-9 Ray Optics and Optical Instruments, with answers and explanations. These are sample questions; the exam has its own separate question set.

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.

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.

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°.

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°.

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.