CBSE Class 10 Science Chapter 9 Light — Reflection and Refraction — 20 MCQs with Answers

Spherical mirrors — both concave and convex — follow the mirror formula 1/f = 1/v + 1/u, where f is focal length, v is image distance, and u is object distance. The NCERT defines sign convention: distances measured against the direction of incident light are negative. Questions in this section test your ability to apply the formula, interpret ray diagrams, and predict image characteristics (real/virtual, magnified/diminished, inverted/erect). Common traps include sign errors and confusion between concave and convex mirror behaviour. CBSE examiners often ask which mirror produces a diminished virtual image or what happens when an object is placed between the pole and focus of a concave mirror.

Refraction is the bending of light when it passes from one transparent medium to another due to change in speed. NCERT states the laws: (1) incident ray, refracted ray, and normal lie in one plane; (2) Snell's law: n₁ sin i = n₂ sin r. Refractive index n = speed of light in vacuum / speed in medium = sin i / sin r (for air-medium interface). Absolute refractive index of water ≈ 1.33, glass ≈ 1.5. Questions test numerical substitution, comparison of optical densities, and direction of bending. A ray bends towards the normal when entering a denser medium and away when entering a rarer medium. CBSE often asks which medium is optically denser or calculates refractive index from given angles.

The lens formula is 1/f = 1/v – 1/u, where f is focal length, v is image distance, u is object distance (measured from optical centre). Convex lens has positive focal length; concave lens negative. Power P = 1/f (in metres), measured in dioptres (D). NCERT emphasizes sign convention: object side is negative, image side is positive for real images, negative for virtual. Magnification m = v/u = h'/h. Questions test formula application, power calculation, and interpretation of sign. CBSE regularly asks: if focal length is 20 cm, power is +5 D; if an object at 30 cm produces an image at 60 cm, find focal length and magnification.

CBSE questions frequently test whether students apply the New Cartesian Sign Convention correctly. For mirrors and lenses: distances measured against incident light are negative; heights above principal axis are positive. Focal length of concave mirror and concave lens is negative; convex mirror and convex lens positive. Magnification m = h'/h = v/u. Positive m means erect image, negative means inverted. |m| > 1 indicates magnified, |m| < 1 diminished. NCERT provides worked examples with sign discipline; reproducing that discipline under exam pressure is key. Common mistakes: forgetting to use negative sign for object distance, confusing v and u, misinterpreting magnification sign.

CBSE introduced assertion-reason MCQs in 2020–21 and they now appear regularly in the board paper. Format: two statements — Assertion (A) and Reason (R). Options: (a) Both A and R true, R correct explanation of A; (b) Both true, R not correct explanation; (c) A true, R false; (d) A false, R true. You must evaluate each statement independently, then check logical linkage. HOTS questions demand conceptual depth: e.g. why does a concave lens never form a real image, or why can't you use a convex mirror as a shaving mirror. NCERT explanations are the gold standard here — read the 'In-Text Questions' and 'Exercises' carefully. These MCQs reward understanding over rote memory.

In the 2025 CBSE Class 10 Science paper (Term or annual), Section A typically contains 16–20 MCQs worth 1 mark each, including 2–3 assertion-reason questions. Speed and accuracy are crucial: you have roughly 1 minute per MCQ. Read the question stem carefully; underline keywords like 'not', 'always', 'never'. Eliminate obviously wrong options first. For numerical MCQs, write the formula in margin, substitute with correct signs, and check units. For assertion-reason, evaluate A and R separately before looking at options. If unsure, mark for review and return after finishing easier sections. Never leave an MCQ blank — there is no negative marking. Practice at least 50 MCQs from NCERT Exemplar, previous years, and this page before the exam. CBSETUTOR.ai users can upload doubt MCQs via photo and get step-by-step solutions instantly, helping you learn the correct approach under expert guidance at just ₹999/month for all subjects across classes 6–12. A 3-day free trial lets you test the AI tutor before committing.

Even well-prepared students lose marks on MCQs due to avoidable errors. Sign convention slip-ups are the number one reason: forgetting that object distance u is always negative, or assuming focal length of concave mirror is positive. Second common mistake is confusing the lens formula 1/f = 1/v – 1/u with the mirror formula 1/f = 1/v + 1/u. Third pitfall: misinterpreting magnification — forgetting that negative m means inverted image, not diminished. Fourth: unit confusion — calculating power in cm instead of metres. Fifth: in assertion-reason, marking (a) when R is true but does not explain A. Sixth: ignoring the question context — e.g. answering for concave lens when the question specifies convex. Drilling these MCQs and reviewing mistakes immediately will wire correct habits. Many students on CBSETUTOR.ai report that uploading incorrect MCQ images and reading the AI explanation within seconds cements concepts faster than passive reading.

Chapter 9 is one of the most predictable chapters in CBSE Class 10 Science. Every year, 3–4 MCQs appear from reflection by spherical mirrors, lens formula, refractive index, and laws of refraction. NCERT provides 15 in-text questions and 12 exercise problems; Board MCQs are often direct lifts or slight numerical tweaks of these. The NCERT Exemplar has another 20 MCQs on this chapter. If you solve these 47 questions twice and understand every step, you will score full marks in this section. The key is not to memorize answers but to internalize the sign convention and formula structure. Write the formula every time, substitute with signs, and simplify carefully. Speed comes from repetition. Students who score 19/20 or 20/20 in MCQs are those who have solved past papers from 2018 to 2024, identified recurring question types, and practiced under timed conditions. CBSETUTOR.ai curates chapter-wise MCQ sets aligned to CBSE pattern and gives instant feedback when you upload your attempt via photo, making practice efficient and targeted.