Mirror equation: 1/v + 1/u = 1/f. Sign convention: distances along principal axis from pole, positive in direction of incident light. Focal length f = R/2 (R = radius of curvature).
-- NCERT Class 12 Physics, Ch. 9, p. 222Reflection Light
8 MCQs1 revision card9-step worked example
Source: NCERT OpticsOfficial key: NTA-verifiedLast updated: 21 Sep 2026
Reflection Light, explained for NEET
The reflection questions that cost marks are rarely about the law itself. They are about the geometry you assume before you apply it — where the normal points, and what the mirror's centre of curvature has to do with its focus.
Start with the law, stated in NCERT Class 12 Physics Chapter 9, page 222: the angle of incidence equals the angle of reflection, and the incident ray, the reflected ray, and the normal all lie in one plane. Both angles are measured from the normal, not from the surface. A ray striking a plane mirror at 30° to the surface has an angle of incidence of 60°, and NEET stems phrase it that way deliberately.
For a spherical mirror, the normal at any point is the radius — the line joining that point to the centre of curvature C. That single fact generates everything else. A ray travelling along the radius hits the surface along its own normal, so the angle of incidence is zero and the ray retraces its path. Apply the law to a paraxial ray parallel to the axis and the geometry gives the focus at the midpoint of PC, so f = R/2. The focal length is not an independent property of the mirror; it is fixed by how sharply the surface curves.
Two consequences worth holding. First, reflection at a rough surface still obeys the same law at every point — the normals simply point in different directions, which is why a wall scatters rather than images. Second, a plane mirror is the R → ∞ limit, so f → ∞, and the image is always virtual, erect, and laterally inverted at equal distance behind.
Where this feeds forward: once you have f = R/2, the mirror formula and magnification are arithmetic. Those are separate lessons. What you must not carry forward is a sloppy normal.
Watch-out: when a stem gives a glancing angle or a deviation angle rather than an angle of incidence, convert to the normal-referenced angle before anything else.
Can you answer these Reflection Light MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
According to the laws of reflection, the angle of incidence and the angle of reflection are both measured with respect to the
Show answer and why every option is right or wrong
Answer: D. D is correct. NCERT Class 12 Physics Chapter 9, page 222, states the law of reflection with both angles measured from the normal drawn at the point of incidence.
Why A is wrong: A is wrong because angles measured from the surface are the complements of the true angles; stems that quote a surface-referenced angle are testing exactly this conversion.
Why B is wrong: B is wrong because the principal axis is a reference line for the mirror as a whole, not for an individual ray; a ray striking off-axis has a normal that is not parallel to the axis.
Why C is wrong: C is wrong because the object-image line plays no part in the statement of the law; it is a construction used afterwards, not a reference for measuring incidence.
MCQ 2Easy RecallPractice
The laws of reflection require that the incident ray, the reflected ray and the normal at the point of incidence
Show answer and why every option is right or wrong
Answer: C. C is correct. The coplanarity condition is the second half of the law of reflection as given in NCERT Class 12 Physics Chapter 9, page 222.
Why A is wrong: A is wrong because it contradicts the coplanarity requirement, which is what makes ray diagrams two-dimensional in the first place.
Why B is wrong: B is wrong because only the special case of normal incidence brings the rays onto the normal; in general the incident and reflected rays make equal non-right angles with it.
Why D is wrong: D is wrong because it states a true but different relation — the equal angles in the law are with the normal, and quoting the surface instead is the standard reference-line slip.
MCQ 3Direct ApplicationPractice
A ray of light strikes a plane mirror so that it makes an angle of 25° with the mirror surface. The angle of reflection is
Show answer and why every option is right or wrong
Answer: C. C is correct. The angle with the surface is 25°, so the angle from the normal is 90° − 25° = 65°, and reflection preserves it (NCERT Class 12 Physics Chapter 9, page 222).
Why A is wrong: A is wrong because it reports the surface-referenced angle unchanged, skipping the conversion to the normal that the law requires.
Why B is wrong: B is wrong because it doubles the surface angle; doubling belongs to the angle between the incident and reflected rays, not to a single angle of reflection.
Why D is wrong: D is wrong because 130° is the total angle between incident and reflected rays (2 × 65°), not the angle of reflection of one ray.
MCQ 4Easy RecallPractice
For a spherical mirror, the normal drawn at any point on the reflecting surface lies along the
Show answer and why every option is right or wrong
Answer: B. B is correct. A spherical surface is part of a sphere, so its normal at any point is radial — this is the geometric premise behind every mirror result in NCERT Class 12 Physics Chapter 9, page 222 onward.
Why A is wrong: A is wrong because the tangent lies in the surface and is perpendicular to the normal, so using it would make every angle of incidence the complement of its true value.
Why C is wrong: C is wrong because only the pole has a normal along the axis; at every other point the radius is inclined to it, which is precisely why off-axis rays converge.
Why D is wrong: D is wrong because the focus is a derived point, midway along the radius for paraxial rays; the normal runs to C, not to F.
MCQ 5Direct ApplicationPractice
A ray of light is directed at a concave mirror along a line passing through its centre of curvature. After striking the mirror, the ray
Show answer and why every option is right or wrong
Answer: A. A is correct. A ray along a radius strikes the surface along its own normal, so the angle of incidence is zero and the reflected ray returns along the same line (NCERT Class 12 Physics Chapter 9, page 222).
Why B is wrong: B is wrong because it applies the parallel-ray rule to the wrong ray; only a ray parallel to the axis is directed to the focus after reflection.
Why C is wrong: C is wrong because it states the reverse of the focal-ray rule — a ray through F emerges parallel, which is a different incident ray from this one.
Why D is wrong: D is wrong because no reflected ray travels along the tangent; the tangent lies in the surface, and reflection returns the ray into the medium.
MCQ 6Direct ApplicationPractice
A concave mirror has a radius of curvature of magnitude 3.60 × 10⁻¹ m. The magnitude of its focal length is
Show answer and why every option is right or wrong
Answer: D. D is correct. Applying the law of reflection to paraxial rays places the focus midway between pole and centre of curvature, giving |f| = |R| / 2 = 1.80 × 10⁻¹ m (NCERT Class 12 Physics Chapter 9, page 222).
Why A is wrong: A is wrong because it divides R by 4; the focal point bisects PC once, not twice.
Why B is wrong: B is wrong because it doubles R instead of halving it, inverting the f = R/2 relation.
Why C is wrong: C is wrong because it equates f with R, treating the centre of curvature and the focus as the same point — they coincide only in the R → 0 limit, which no real mirror occupies.
MCQ 7Concept TrapPractice
Light falls on a sheet of unpolished white paper and is scattered in all directions rather than forming an image. At the microscopic level, this happens because
Show answer and why every option is right or wrong
Answer: A. A is correct. Diffuse reflection obeys the same law everywhere; the surface's microscopic irregularity means each point has its own normal direction, so the reflected rays leave in many directions (NCERT Class 12 Physics Chapter 9, page 222).
Why B is wrong: B is wrong because equality of the two angles is the law itself, and a rough surface does not modify it — it only changes what the normal is.
Why C is wrong: C is wrong because it treats the law as a property of smooth surfaces only; the law is local and applies at every point regardless of surface finish.
Why D is wrong: D is wrong because coplanarity holds at each point of incidence; the plane simply differs from point to point, which is not the same as coplanarity failing.
MCQ 8CalculationPractice
A ray strikes a plane mirror at an angle of incidence of 40.0°. The mirror is then rotated through 15.0° about an axis in its own plane and perpendicular to the plane of incidence, while the incident ray is kept fixed. The angle between the original reflected ray and the new reflected ray is
Show answer and why every option is right or wrong
Answer: B. B is correct. Rotating the mirror by 15.0° turns the normal by 15.0°, so the new angle of incidence is 55.0° and the reflected ray shifts by twice the mirror rotation: 2 × 15.0° = 30.0° (law of reflection, NCERT Class 12 Physics Chapter 9, page 222).
Why A is wrong: A is wrong because it halves the mirror rotation; the reflected ray turns through twice the mirror's rotation, not half of it.
Why C is wrong: C is wrong because it assumes the reflected ray turns by the same angle as the mirror, ignoring that both the incidence and reflection angles change by 15.0° each.
Why D is wrong: D is wrong because 55.0° is the new angle of incidence measured from the rotated normal, not the angular separation between the two reflected rays.
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Reflection Light: quick recall before you leave
How do you solve a Reflection Light question? A worked example
- 1
Given
A ray of light is incident on a plane mirror, making an angle of 20.0° with the plane of the mirror. The mirror is then rotated about an axis lying in its plane and perpendicular to the plane of incidence, through 12.0°, in the sense that increases the angle of incidence. The incident ray is unchanged.
- 2
Required
(a) the angle of reflection before rotation, and (b) the angle through which the reflected ray turns.
- 3
Concept
The law of reflection fixes the reflected ray's direction relative to the normal. Rotating the mirror rotates its normal by the same amount, so both the incidence and the reflection angles change — and the reflected ray swings through the sum of those two changes.
- 4
Formula
angle of incidence i = angle of reflection r, with both measured from the normal. For a surface-referenced angle θ_s, i = 90° − θ_s. For a mirror rotation α with a fixed incident ray, the reflected ray turns through 2α.
- 5
Substitution
θ_s = 20.0°, so i = 90° − 20.0° = 70.0°. Mirror rotation α = 12.0°.
- 6
Calculation
(a) r = i = 70.0°.
(b) After rotation, the normal has turned by 12.0°, so the new angle of incidence is 70.0° + 12.0° = 82.0°, and the new angle of reflection is also 82.0°. The reflected ray's direction is set by the normal, which has moved 12.0°, plus the extra 12.0° opening of the reflection angle: total turn = 2 × 12.0° = 24.0°.
The 90° used in the surface-to-normal conversion and the factor 2 in "2α" are both exact — a right angle by definition and a counting factor respectively — so neither limits the significant figures. The data carry three significant figures, and so do the answers. - 7
Final answer
(a) 70.0° (b) 24.0°
- 8
Common trap
Reading "20.0° with the mirror" as the angle of incidence and answering 20.0° for part (a). The law is stated for normal-referenced angles only; every surface-referenced or glancing angle in a stem must be converted first. The same slip in part (b) produces 12.0° — reporting the mirror's rotation as the ray's rotation, which forgets that the reflection angle opens by α as well as the normal turning by α.
- 9
Similar NEET-style question
A ray of light makes a glancing angle of 35.0° with a plane mirror. The mirror is rotated through 8.00° about an axis in its own plane perpendicular to the plane of incidence, the incident ray being fixed. Find the angle between the incident ray and the reflected ray after the rotation.
What to remember before solving Reflection Light questions
Which Reflection Light formulas do you need for NEET?
1 formula — click to collapse
Mirror formula
Spherical mirror formula. Sign convention: distances from pole, positive in direction of incident light.
| Symbol | Quantity | SI Unit |
|---|---|---|
| v | image distance | m |
| u | object distance | m |
| f | focal length | m |
| m | magnification | - |
Valid when
- Spherical mirror, paraxial rays
- Sign convention used consistently
More in Optics: 9 exam traps and mistakes · 10 formulas · 7 question patterns from its other lessons.
Reflection Light questions from past NEET papers
No question in our NEET 2020–2025 set targets this topic directly.
Sources
NCERT refs: Class 12 Physics Chapter 9, p.222
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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