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Ray Optics is one of the biggest scorers in NEET(UG) Physics, and the questions are rarely hard. They are lost on sign conventions and on confusing the mirror formula with the lens formula. Ten questions below, with the answer key and a hint for each.
What this chapter carries in NEET(UG)
- Usually 3 to 4 questions every year, which is 12 to 16 marks.
- Most of them come from mirrors, lenses, refraction, total internal reflection and lens power.
- Learn one sign convention and stay with it. Mixing two is what costs marks.
What the syllabus says
In the syllabus (Unit 16, Optics): Reflection of light, spherical mirrors and the mirror formula, refraction of light at plane and spherical surfaces, the thin lens formula and the lens maker’s formula, total internal reflection and its applications, magnification, power of a lens, thin lenses in contact, refraction of light through a prism, and the microscope and the astronomical telescope, both reflecting and refracting, with their magnifying powers.
Taken out in 2024: deviation and dispersion of light by a prism, so dispersive power and angular dispersion go with it; the human eye, image formation and accommodation, and the correction of myopia and hypermetropia; scattering of light and the blue colour of the sky.
Taken from the NMC syllabus for NEET (UG) 2026, the latest one published. See the full syllabus, unit by unit.
Formulas you must know by heart
| Mirror formula | 1/v + 1/u = 1/f |
| Focal length of a spherical mirror | f = R/2 |
| Lens formula | 1/v − 1/u = 1/f |
| Magnification | m = v/u (lens), m = −v/u (mirror) |
| Refractive index | n = c/v |
| Snell’s law | n1 sin i = n2 sin r |
| Critical angle | sin C = 1/n |
| Power of a lens | P = 1/f, with f in metres, P in dioptres |
| Lenses in contact | P = P1 + P2 |
The mirror formula adds the two terms, the lens formula subtracts. That single difference causes more wrong answers in this chapter than anything else.
Ten questions. Give yourself ten minutes.
Write your answers down before you scroll. A question you looked up is a question you have not answered.
Q1. A concave mirror has a radius of curvature of 20 cm. Its focal length is
- (a) 5 cm
- (b) 10 cm
- (c) 20 cm
- (d) 40 cm
Q2. The speed of light in a medium of refractive index 1.5 is about
- (a) 1.5 × 108 m/s
- (b) 2 × 108 m/s
- (c) 3 × 108 m/s
- (d) 4.5 × 108 m/s
Q3. For a medium of refractive index 1.5, the sine of the critical angle is
- (a) 1/3
- (b) 2/3
- (c) 3/2
- (d) 1
Q4. The power of a convex lens of focal length 50 cm is
- (a) +0.5 D
- (b) +2 D
- (c) +5 D
- (d) +50 D
Q5. Total internal reflection can take place only when light travels
- (a) from a rarer to a denser medium
- (b) from a denser to a rarer medium
- (c) in a single medium
- (d) along the normal
Q6. An object is placed at a distance 2f in front of a convex lens of focal length f. The image formed is
- (a) at f, real and smaller
- (b) at 2f, real, inverted and the same size
- (c) at infinity
- (d) virtual and larger
Q7. Two thin lenses of powers +2 D and +3 D are placed in contact. The power of the combination is
- (a) +1 D
- (b) +1.5 D
- (c) +5 D
- (d) +6 D
Q8. The formula connecting object distance, image distance and focal length for a mirror is
- (a) 1/v − 1/u = 1/f
- (b) 1/v + 1/u = 1/f
- (c) v + u = f
- (d) v − u = f
Q9. A ray of light passes from air into glass. The angle of refraction, compared with the angle of incidence, is
- (a) larger
- (b) smaller
- (c) equal
- (d) always 90°
Q10. A plane mirror forms an image that is
- (a) real and inverted
- (b) real and erect
- (c) virtual and inverted
- (d) virtual, erect and of the same size
Answer key, with a hint for each
| Q1 | (b) | f = R/2 = 20/2 = 10 cm. |
| Q2 | (b) | v = c/n = 3 × 108 / 1.5 = 2 × 108 m/s. |
| Q3 | (b) | sin C = 1/n = 1/1.5 = 2/3. |
| Q4 | (b) | P = 1/f with f in metres: 1/0.5 = +2 D. Convert the centimetres first. |
| Q5 | (b) | It needs the denser to rarer direction, and an angle past the critical angle. |
| Q6 | (b) | At 2f the image comes at 2f on the other side, real, inverted and the same size. |
| Q7 | (c) | Powers of lenses in contact simply add: 2 + 3 = 5 D. |
| Q8 | (b) | The mirror formula adds the terms. The lens formula is the one that subtracts. |
| Q9 | (b) | Going into a denser medium the ray bends towards the normal, so r is smaller than i. |
| Q10 | (d) | A plane mirror always gives a virtual, erect image of the same size, as far behind as the object is in front. |
Now mark yourself honestly
NEET(UG) marks the way it marks. Use the same rule here:
- +4 for a right answer
- −1 for a wrong one
- 0 for a blank
So ten questions here are out of 40. In the real paper, 45 Physics questions are out of 180.
If you scored 32 or more, the basics of this chapter are secure. Move to harder questions, not more of these.
If you scored below 24, do not feel bad about it. You have just found out something useful before the exam did. Go back to the formula table above, learn it properly, and sit these ten again tomorrow.
And if you guessed a few and they landed, count those as wrong. A guess that works once will not work in May.
The full chapter, on a clock
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