Class 9 Science Chapter 13 Light MCQ Quiz: 30 Questions with Detailed Answers

The restructured CBSE Class 9 Science paper allocates 40–50% weightage to objective questions, including MCQs with single correct answers, multiple correct answers, assertion–reason pairs, and case-based scenarios. MCQs test not just rote knowledge but conceptual clarity and the ability to eliminate wrong options under time pressure. In Chapter 13 (Light), examiners focus on core concepts: (1) the laws of reflection and their application to plane mirrors, (2) the nature of images formed by mirrors and lenses, (3) the path of light through a prism and colour separation, and (4) eye defects and their correction. Unlike descriptive questions, MCQs demand precision—one wrong word in a definition, and your answer is marked incorrect. The new pattern also includes assertion–reason MCQs, where both statement and reason must be true, and the reason must logically explain the statement. Mastering MCQ patterns now builds the muscle memory needed for speed and accuracy during the board exam. Each question below mirrors real CBSE standards and includes reasoning to help you understand why wrong options are traps.

**Q1.** According to the law of reflection, the angle of incidence is: (A) Always 90° (B) Equal to the angle of reflection (C) Greater than the angle of reflection (D) Independent of the angle of reflection **Answer:** (B) **Reason:** The law of reflection states that ∠i = ∠r, where both angles are measured from the normal. **Q2.** A ray of light hits a plane mirror at an angle of incidence of 35°. The angle of reflection will be: (A) 35° (B) 55° (C) 70° (D) 90° **Answer:** (A) **Reason:** By the law of reflection, angle of reflection = angle of incidence = 35°. **Q3.** The image formed by a plane mirror is always: (A) Real and inverted (B) Virtual and erect (C) Real and erect (D) Virtual and inverted **Answer:** (B) **Reason:** Plane mirrors form virtual images (light rays don't actually meet) that are erect and the same size as the object. **Q4.** Which of the following is NOT a property of light? (A) It travels in straight lines (B) It requires a medium to propagate (C) It can be reflected (D) It can be refracted **Answer:** (B) **Reason:** Light can travel through vacuum (as it reaches us from the Sun); it does not need a medium. **Q5.** The normal to a reflecting surface: (A) Is parallel to the surface (B) Is perpendicular to the surface (C) Makes an angle of 45° with the surface (D) Depends on the angle of incidence **Answer:** (B) **Reason:** The normal is always drawn perpendicular to the reflecting surface at the point of incidence. **Q6.** When light travels from a denser to a rarer medium, it: (A) Bends towards the normal (B) Bends away from the normal (C) Travels parallel to the normal (D) Stops propagating **Answer:** (B) **Reason:** Snell's law states that when light moves from dense to rarer medium, the refracted ray bends away from the normal. **Q7.** The refractive index of a medium is defined as: (A) Speed of light in medium ÷ speed of light in vacuum (B) Speed of light in vacuum ÷ speed of light in medium (C) Angle of incidence ÷ angle of refraction (D) Density of the medium **Answer:** (B) **Reason:** Refractive index n = c/v, where c is speed in vacuum (~3 × 10⁸ m/s) and v is speed in the medium. **Q8.** A ray of light hits a mirror and reflects back along the same path. The angle of incidence must be: (A) 0° (B) 45° (C) 90° (D) 180° **Answer:** (A) **Reason:** When ∠i = 0°, the ray hits the normal perpendicularly and reflects straight back (∠r = 0° too). **Q9.** Which colour has the smallest wavelength in the visible spectrum? (A) Red (B) Green (C) Violet (D) Yellow **Answer:** (C) **Reason:** Violet light (~380–420 nm) has the shortest wavelength; red (~700–750 nm) is the longest. **Q10.** Dispersion of white light occurs because: (A) Different colours have different speeds in a medium (B) All colours have the same speed in glass (C) The mirror reflects different colours differently (D) The prism absorbs some colours **Answer:** (A) **Reason:** Refractive index varies with wavelength; shorter wavelengths (violet) bend more than longer ones (red) in a prism.

**Q11.** Two plane mirrors are placed at an angle of 90° to each other. An object is placed between them. The number of images formed is: (A) 2 (B) 3 (C) 4 (D) Infinite **Answer:** (B) **Reason:** Number of images = (360°/θ) − 1 = (360°/90°) − 1 = 4 − 1 = 3. **Q12.** When white light passes through a prism, the light that deviates the most is: (A) Red (B) Yellow (C) Green (D) Violet **Answer:** (D) **Reason:** Violet has the highest refractive index in glass, so it bends most; red bends least. **Q13.** A person suffers from myopia (short-sightedness). This occurs because: (A) The eyeball is too short (B) The cornea is too flat (C) The eyeball is too long or cornea is too curved (D) The lens is too weak **Answer:** (C) **Reason:** Myopia causes distant light rays to focus in front of the retina; the eye converges too much. **Q14.** The near point of a normal human eye is: (A) 25 cm (B) 50 cm (C) 10 cm (D) 15 cm **Answer:** (A) **Reason:** The near point (minimum distance for clear vision without strain) is approximately 25 cm for healthy adults. **Q15.** A convex lens is used to correct: (A) Myopia (B) Hyperopia (C) Astigmatism (D) Presbyopia **Answer:** (B) **Reason:** Hyperopia (far-sightedness) requires a converging lens to add optical power and focus light on the retina. **Q16.** The angle of deviation of a ray through a prism is the angle between: (A) The incident ray and refracted ray (B) The incident ray and emergent ray (C) The emergent ray and the base of the prism (D) The two faces of the prism **Answer:** (B) **Reason:** Deviation is measured as the angle δ between the incident and emergent rays outside the prism. **Q17.** If two mirrors form an angle of 60° between them and an object is placed between them, the total number of images formed is: (A) 5 (B) 6 (C) 7 (D) 8 **Answer:** (A) **Reason:** Number of images = (360°/60°) − 1 = 6 − 1 = 5. **Q18.** Presbyopia is a vision defect that occurs when: (A) The cornea becomes too curved (B) The ciliary muscles weaken with age (C) The eyeball becomes too long (D) The pupil shrinks **Answer:** (B) **Reason:** Presbyopia develops in older people when the ciliary muscles lose elasticity and cannot adjust the lens's focal length. **Q19.** Rainbow formation is an example of: (A) Reflection only (B) Refraction only (C) Dispersion only (D) Reflection, refraction, and dispersion combined **Answer:** (D) **Reason:** Rainbows form when sunlight is refracted into water droplets, internally reflected, and dispersed into colours. **Q20.** The human eye can see an object clearly only if the image is formed on the: (A) Cornea (B) Iris (C) Retina (D) Lens **Answer:** (C) **Reason:** The retina contains photoreceptor cells (rods and cones) that detect light and send signals to the brain.

**Q21. Assertion:** The angle of incidence equals the angle of reflection for all types of reflecting surfaces. **Reason:** The law of reflection applies only to plane mirrors. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true, but R is false (D) A is false, but R is true **Answer:** (C) **Reason:** The law of reflection (∠i = ∠r) applies to plane, concave, and convex mirrors; R incorrectly limits it to plane mirrors. **Q22. Assertion:** When white light is dispersed by a prism, red light emerges at a greater angle to the normal than violet light. **Reason:** Red light has a lower refractive index than violet light in glass. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true, but R is false (D) A is false, but R is true **Answer:** (A) **Reason:** Lower refractive index means less bending; red (n ≈ 1.51) bends less than violet (n ≈ 1.53), so red emerges at a larger angle from the normal. **Q23. Assertion:** A person with myopia can see distant objects clearly using a concave lens. **Reason:** A concave lens diverges light rays and reduces the optical power of the eye. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is false, but R is true (D) A is true, but R is false **Answer:** (A) **Reason:** Myopia causes light to focus in front of the retina; a concave lens diverges rays to shift focus onto the retina. **Q24. Assertion:** If two mirrors are placed at an angle of 45° to each other, the number of images formed by an object is 7. **Reason:** The formula for the number of images is (360°/θ) − 1, where θ is the angle between mirrors. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is false, but R is true (D) A is true, but R is false **Answer:** (A) **Reason:** Number of images = (360°/45°) − 1 = 8 − 1 = 7; the formula and calculation are both correct. **Q25. Assertion:** The critical angle for total internal reflection is larger for a medium with a smaller refractive index. **Reason:** Critical angle θc = sin⁻¹(1/n), where n is the refractive index of the denser medium. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is false, but R is true (D) A is true, but R is false **Answer:** (A) **Reason:** As n decreases, 1/n increases, so sin⁻¹(1/n) increases, making θc larger. **Q26. Assertion:** The pupil of the human eye contracts when light intensity increases. **Reason:** Contraction reduces the amount of light entering the eye and protects the retina. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true, but R is false (D) A is false, but R is true **Answer:** (A) **Reason:** Pupil dilation/constriction is a reflex that controls light entry; smaller pupil = less light on retina. **Q27. Assertion:** Hyperopia can be corrected using a bifocal lens that has both a convex and concave part. **Reason:** The convex part focuses light on the retina for near vision, while the concave part is used for distant vision. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is false, but R is true (D) A is true, but R is false **Answer:** (C) **Reason:** Bifocals are used for presbyopia (mixed near and far defects), not pure hyperopia; the convex part actually helps both near and distant vision in hyperopia. **Q28. Assertion:** The speed of light in a medium is always less than its speed in vacuum. **Reason:** Light travels slower in media with higher refractive indices. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true, but R is false (D) A is false, but R is true **Answer:** (A) **Reason:** v = c/n; since n > 1 for all media, v < c always. Higher n means greater optical density and slower light propagation. **Q29. Assertion:** A plane mirror always produces a virtual image that is the same distance from the mirror as the object. **Reason:** The image distance equals the object distance because the angle of incidence always equals the angle of reflection. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true, but R is false (D) A is false, but R is true **Answer:** (B) **Reason:** Both are true, but the law of reflection is not the direct reason; it's the geometry of reflected rays diverging from a virtual point behind the mirror. **Q30. Assertion:** When a ray of light undergoes total internal reflection at a boundary, the emergent ray is absent. **Reason:** At the critical angle, the refracted ray travels along the interface (angle of refraction = 90°), and beyond it, no refraction occurs. (A) Both A and R are true, and R is the correct explanation of A (B) Both A and R are true, but R is NOT the correct explanation of A (C) A is true, but R is false (D) A is false, but R is true **Answer:** (A) **Reason:** Beyond the critical angle, all light reflects back into the denser medium; there is no emergent ray because total internal reflection occurs.

CBSE MCQs often include plausible but incorrect options designed to catch students who half-understand concepts. Here are the most common traps in Chapter 13 Light: **Trap 1: Confusing angle of incidence with angle of deviation.** Many students think ∠i = ∠d or assume deviation equals refraction. Remember: deviation is the net change in ray direction after passing through a prism; it is not the same as the angle of refraction. **Trap 2: Mixing up lens types for vision defects.** Myopia corrects with a concave lens (not convex); hyperopia corrects with a convex lens (not concave). A common trap is listing both types for presbyopia, which does require bifocals. Test: *If you see "convex lens" for myopia, eliminate immediately.* **Trap 3: Reversing colour order in dispersion.** Violet bends more (higher refractive index), red bends less. Some options swap this. Remember the acronym ROYGBIV: Red bends least, Violet bends most. **Trap 4: Assuming 'angle of incidence' always equals a specific number.** Many students default to 45° or 90°. The law is ∠i = ∠r, but ∠i itself varies based on how the ray strikes the surface. **Trap 5: Stating light "needs" a medium.** Light propagates through vacuum (it doesn't need air or water). Options saying "light requires a medium" are false. **Trap 6: Confusing image distance with object distance in mirrors.** While plane mirrors form images at equal distances, curved mirrors do not. A distractor might say "image distance is always half the object distance"—wrong. **Trap 7: Missing the word "virtual" or "real".** A plane mirror forms a virtual image. If an option says "real", eliminate it. Conversely, a concave mirror can form real images—many students mistakenly think concave mirrors only form virtual images. **Trap 8: Forgetting the near and far points of the eye.** The near point is ~25 cm (not 10 or 50 cm); the far point for a normal eye is infinity. MCQs test whether you know these exact values. **Trap 9: Mixing reflection and refraction.** Reflection is the bouncing of light off a surface (angle of incidence = angle of reflection). Refraction is bending as light enters a new medium (Snell's law applies). Some options blur these—read carefully. **Trap 10: In assertion–reason, choosing (B) when both are true but unrelated.** For example, "The law of reflection applies to plane mirrors" (A is true), and "Water has a higher refractive index than air" (R is true), but R does NOT explain A. Choose (B) in such cases, not (A).

In a CBSE Class 9 Science board exam (80 marks, 3 hours), multiple-choice questions typically occupy 24–32 marks and must be completed in 40–50 minutes to leave time for long-answer questions. Here's a proven strategy: **Step 1: Triage (5 minutes total)** Don't solve sequentially. Scan all MCQs first. Mark every question as: - **Green:** You can answer in ≤30 seconds (straightforward factual recall). - **Yellow:** Requires thought but solvable in 60–90 seconds (application or numerical). - **Red:** Assertion–reason or unfamiliar; skip for now. Typically, 40–50% will be green, 35–40% yellow, and 10–15% red. **Step 2: Solve Green Questions (12–15 minutes)** Answer all green questions first. These build momentum and accumulate marks quickly. For Chapter 13 Light, green questions include: "Which colour has the smallest wavelength?" (Violet) or "A plane mirror forms which type of image?" (Virtual and erect). No second-guessing—if you know it, mark and move on. **Step 3: Attempt Yellow Questions (20–25 minutes)** Work through yellow questions at a steady pace. For numerical ones (e.g., calculating number of images with the formula (360°/θ) − 1), jot the formula on scrap paper, substitute, and solve. If stuck after 60 seconds, mark and return later. **Step 4: Smart Guessing on Red (5–10 minutes)** For assertion–reason MCQs: - Read the assertion first. If you know it's false, eliminate (A) and (B) immediately. - If the assertion is true, check if the reason is also true. If yes, verify the logical link. - If unsure of the reason, use elimination: statements that are too broad ("always", "never") or unrelated are often wrong. For dispersion/vision defect questions you didn't solve: - Eliminate trap options first. "Red bends more than violet in a prism" → eliminate (it's false). - Use context: if the question is about hyperopia and you see "concave lens", eliminate (concave is for myopia). **Step 5: Review (3–5 minutes)** Revisit yellow questions you flagged. Often, a second reading clarifies the confusion. Check your answer once more; don't change unless certain. **Timing Benchmark:** - Green questions: 15–20 seconds each. - Yellow questions: 60–90 seconds each. - Red questions: 30 seconds for smart guessing. - Total MCQ time: 45–50 minutes, leaving 130–135 minutes for short and long answers. **Final Tip:** Practice with a timer. Set a 45-minute block on your phone, complete 30 Light MCQs under pressure, and score yourself. Repeat twice a week in the month before the exam. This builds speed and confidence.