Q1. What happens if you look at the Sun directly or through a lens?
a) Nothing happens
b) Your eyes will see a larger Sun
c) You may damage your eyes
d) You will see a rainbow
Answer: You may damage your eyes.
Why correct: The intense sunlight can burn the retina, causing permanent eye damage. Lenses concentrate sunlight, increasing the danger.
Why others wrong: (a) Sunlight is harmful; (b) magnification isn’t relevant; (d) rainbow formation requires prisms, not lenses.
Q2. When a convex lens focuses sunlight on paper, what is formed?
a) A virtual image
b) A real image
c) An upright image
d) A magnified image
Answer: A real image.
Why correct: Sunlight converges at a point on paper, forming an actual real image.
Why others wrong: (a) virtual images cannot be projected; (c) upright is not relevant here; (d) the Sun’s image is actually very small.
Q3. Why does the paper burn when sunlight is focused by a convex lens?
a) Sunlight becomes coloured
b) Lens produces chemical reactions
c) Sunlight is concentrated at one point
d) Sunlight cools the paper
Answer: Sunlight is concentrated at one point.
Why correct: Concentrated heat raises the temperature enough to ignite paper.
Why others wrong: (a) colour doesn’t cause burning; (b) no chemical reaction from lens; (d) sunlight heats, not cools.
Q4. The bright spot formed on paper by a convex lens is:
a) A virtual image of the Sun
b) A real image of the Sun
c) A shadow of the Sun
d) A reflection of the Sun
Answer: A real image of the Sun.
Why correct: The converging rays form an actual inverted tiny image of the Sun.
Why others wrong: (a) virtual cannot be caught on screen; (c) not a shadow; (d) no reflection involved.
Q5. Rays coming from the Sun are considered:
a) Divergent
b) Parallel
c) Random
d) Curved
Answer: Parallel.
Why correct: The Sun is far away, making rays nearly parallel.
Why others wrong: (a) divergence is negligible; (c) not random; (d) rays travel straight.
Q6. Parallel rays falling on a convex lens:
a) Diverge
b) Do not change direction
c) Converge to a point
d) Form no image
Answer: Converge to a point.
Why correct: Convex lenses bend rays inward to the focus.
Why others wrong: (a) divergence is for concave lens; (b) they DO bend; (d) image forms.
Q7. The point where parallel rays converge after a convex lens:
a) Optical centre
b) Pole
c) Principal focus
d) Aperture
Answer: Principal focus.
Why correct: Defined as the point where parallel rays meet after refraction.
Why others wrong: (a) centre of lens; (b) mirror term; (d) opening size.
Q8. For a concave lens, parallel rays after refraction:
a) Converge
b) Appear to diverge from a point
c) Do not bend
d) Get reflected
Answer: Appear to diverge from a point.
Why correct: Concave lens causes rays to spread out but they seem to come from a virtual focus.
Why others wrong: (a) concave never converges; (c) rays bend; (d) lenses refract, not reflect.
Q9. A lens has how many principal foci?
a) Zero
b) One
c) Two
d) Three
Answer: Two.
Why correct: Lenses allow light from both sides, so two foci exist.
Why others wrong: (a) incorrect; (b) only mirrors have one effective focus; (d) no three-focus lens.
Q10. Distance between optical centre and principal focus:
a) Aperture
b) Diameter
c) Focal length
d) Magnification
Answer: Focal length.
Why correct: Definition of focal length.
Why others wrong: (a) width; (b) size; (d) ratio of heights.
Q11. The focal length of a convex lens is:
a) Zero
b) Negative
c) Positive
d) Both
Answer: Positive.
Why correct: Converging lenses have positive focal length by sign convention.
Why others wrong: (b) negative is for concave; (a) meaningless; (d) not applicable.
Q12. The focal length of a concave lens is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: Negative.
Why correct: Concave lenses diverge rays, so f is negative.
Why others wrong: (a) convex; (c) impossible; (d) means no refraction.
Q13. All sign convention measurements for lenses are taken from:
a) Principal focus
b) Pole
c) Optical centre
d) Curved surface
Answer: Optical centre.
Why correct: All distances are measured from the optical centre.
Why others wrong: (a) not measurement point; (b) used for mirrors; (d) irrelevant.
Q14. Lens formula relates:
a) u, v, h
b) u, h, f
c) v, f, h
d) u, v, f
Answer: u, v, f.
Why correct: Lens formula is 1/f = 1/v + 1/u.
Why others wrong: They include height, which is not part of formula.
Q15. Magnification is the ratio of:
a) Object height to image distance
b) Image height to object height
c) Object height to focal length
d) Image distance to object distance
Answer: Image height to object height.
Why correct: Formula m = hᵢ / h₀.
Why others wrong: Other quantities irrelevant or incorrect.
Q16. If m = +2, the image is:
a) Real and inverted
b) Real and erect
c) Virtual and erect
d) Virtual and inverted
Answer: Virtual and erect.
Why correct: Positive magnification → erect virtual image in lenses.
Why others wrong: Real images are inverted (negative m).
Q17. A concave lens always forms an image that is:
a) Real and inverted
b) Real and erect
c) Virtual and erect
d) Virtual and inverted
Answer: Virtual and erect.
Why correct: Concave lenses always produce smaller, virtual, erect images.
Why others wrong: It never forms real or inverted images.
Q18. Concave lens example f = –15 cm, image at –10 cm. Object is at:
a) –10 cm
b) –15 cm
c) –30 cm
d) +30 cm
Answer: –30 cm.
Why correct: Using lens formula, u = –30 cm.
Why others wrong: Other distances do not satisfy the formula.
Q19. If m = –0.33, the negative sign means:
a) Image is larger
b) Image is inverted
c) Image is virtual and erect
d) Image is real
Answer: Image is inverted.
Why correct: Negative magnification indicates inversion.
Why others wrong: Virtual images have +m; real is not indicated by –m alone.
Q20. Convex lens f = +10 cm forms image of object at:
a) –10 cm
b) –15 cm
c) –20 cm
d) +20 cm
Answer: –15 cm.
Why correct: Using lens formula, u = –15 cm.
Why others wrong: Other values don’t satisfy formula.
Q21. Ability of lens to converge/diverge depends on:
a) Thickness
b) Colour
c) Focal length
d) Diameter
Answer: Focal length.
Why correct: Short focal length = stronger bending.
Why others wrong: (a,d) affect size only; (b) irrelevant.
Q22. Power of lens =
a) Product of focal length
b) Reciprocal of focal length
c) Square of focal length
d) Sum of focal lengths
Answer: Reciprocal of focal length.
Why correct: P = 1/f (in metres).
Why others wrong: Other formulas incorrect.
Q23. SI unit of power:
a) Watt
b) Lumen
c) Dioptre
d) Candela
Answer: Dioptre.
Why correct: Lens power unit is dioptre (D).
Why others wrong: Others are for light/energy.
Q24. 1 dioptre corresponds to focal length:
a) 1 m
b) 1 cm
c) 10 m
d) 10 cm
Answer: 1 m.
Why correct: P = 1/f → f = 1 m.
Why others wrong: Do not satisfy formula.
Q25. Power of convex lens is:
a) Positive
b) Negative
c) Zero
d) Variable
Answer: Positive.
Why correct: Converging lenses have + power.
Why others wrong: (b) concave; (c,d) incorrect.
Q26. Power of a concave lens is:
a) Positive
b) Negative
c) Zero
d) Depends on material
Answer: Negative.
Why correct: Concave lenses diverge, so P < 0.
Why others wrong: Other options incorrect.
Q27. A lens with +2 D is:
a) Concave
b) Convex
c) Plane
d) Cylindrical
Answer: Convex.
Why correct: Positive power → convex lens.
Why others wrong: Concave has – power.
Q28. Lens with –2.5 D has focal length:
a) +0.40 m
b) –0.40 m
c) +0.25 m
d) –2.5 m
Answer: –0.40 m.
Why correct: f = 1/P = –0.4 m.
Why others wrong: Others don’t match formula.
Q29. Net power of lenses in contact:
a) Multiply
b) Add (P₁ + P₂ + …)
c) Subtract
d) Divide
Answer: Add.
Why correct: P = P₁ + P₂ + P₃ …
Why others wrong: Other math operations wrong.
Q30. Opticians prefer power because:
a) Looks scientific
b) Easier to add powers
c) Focal length is hard to measure
d) Power never changes
Answer: Easier to add powers.
Why correct: For combinations, addition is simplest.
Why others wrong: Not real reasons.
Q31. Convex lens of short focal length bends rays:
a) Through small angles
b) Through large angles
c) Not at all
d) Backward
Answer: Through large angles.
Why correct: Short focal length = strong lens.
Why others wrong: Others contradict lens behaviour.
Q32. Concave lens of very short focal length has:
a) Low divergence
b) High convergence
c) High divergence
d) No effect
Answer: High divergence.
Why correct: Short focal length → stronger divergence.
Why others wrong: Concave never converges.
Q33. Optical instruments use many lenses to:
a) Reduce brightness
b) Minimise weight
c) Increase magnification and sharpness
d) Make device colourful
Answer: Increase magnification and sharpness.
Why correct: Multiple lenses improve clarity.
Why others wrong: Others are unrelated.
Q34. In lens formula, u is:
a) Aperture
b) Object distance
c) Image distance
d) Focus angle
Answer: Object distance.
Why correct: Defined as distance of object from optical centre.
Why others wrong: Other definitions wrong.
Q35. In lens formula, v is:
a) Object height
b) Image height
c) Image distance
d) Power
Answer: Image distance.
Why correct: v is distance of image from lens.
Why others wrong: Heights are h₀, hᵢ; power unrelated.
Q36. Distance between lens and image of Sun gives:
a) Aperture
b) Focal length
c) Power
d) Thickness
Answer: Focal length.
Why correct: Sun gives parallel rays → focus = focal length.
Why others wrong: Other options irrelevant.
Q37. A concave lens always forms images that are:
a) Real and erect
b) Inverted
c) Smaller than object
d) Larger and real
Answer: Smaller than object.
Why correct: Concave lens produces diminished images.
Why others wrong: Never forms real or inverted images.
Q38. Symbol F represents:
a) Focus
b) Principal focus
c) Optical centre
d) Focal plane
Answer: Principal focus.
Why correct: F denotes principal focus.
Why others wrong: Notations incorrect.
Q39. Magnification also equals:
a) v/u
b) v×u
c) u/v
d) f/u
Answer: v/u.
Why correct: m = v/u for lenses.
Why others wrong: Other formulas wrong.
Q40. Lenses follow sign conventions similar to:
a) Plane mirrors
b) Spherical mirrors
c) Prisms
d) Bulbs
Answer: Spherical mirrors.
Why correct: Both use principal axis and Cartesian sign conventions.
Why others wrong: Other objects do not.
Q41. For concave lens, image distance is always:
a) Positive
b) Negative
c) Zero
d) Greater than u
Answer: Negative.
Why correct: Images formed on same side as object → negative v.
Why others wrong: Other signs impossible.
Q42. Increasing power of convex lens means:
a) Increasing focal length
b) Decreasing focal length
c) Making it flat
d) Making it concave
Answer: Decreasing focal length.
Why correct: P = 1/f → small f = high P.
Why others wrong: Opposite or irrelevant.
Q43. Lens of focal length 0.5 m has power:
a) +1 D
b) +2 D
c) +0.5 D
d) –2 D
Answer: +2 D.
Why correct: P = 1/0.5 = 2 D.
Why others wrong: Wrong calculations.
Q44. Lens of power –1 D has focal length:
a) 1 m
b) –1 m
c) 0.5 m
d) –0.5 m
Answer: –1 m.
Why correct: f = 1/P = –1 m.
Why others wrong: Incorrect reciprocals.
Q45. A virtual image formed by a lens is always:
a) Inverted
b) On opposite side
c) On same side as object
d) Larger only
Answer: On same side as object.
Why correct: Virtual images lie on object’s side.
Why others wrong: Inversion happens for real images, not virtual.
Q46. A real image formed by a lens is always:
a) Inverted
b) Erect
c) Virtual
d) On same side
Answer: Inverted.
Why correct: Real lens images invert.
Why others wrong: Virtual is erect; real cannot be erect.
Q47. Magnification m > 1 means:
a) Image is smaller
b) Same size
c) Larger
d) Inverted
Answer: Image is larger.
Why correct: m > 1 means enlargement.
Why others wrong: Do not match definition.
Q48. Two lenses +1 D and –2 D have net power:
a) –3 D
b) +3 D
c) –1 D
d) +1 D
Answer: –1 D.
Why correct: P = 1 – 2 = –1 D.
Why others wrong: Other sums incorrect.
Q49. A lens with high power bends rays:
a) Not at all
b) Slightly
c) Strongly
d) Randomly
Answer: Strongly.
Why correct: High power = strong curvature = strong bending.
Why others wrong: Opposite or meaningless.
Q50. The plane passing through the principal focus is:
a) Focal plane
b) Image plane
c) Optical plane
d) Object plane
Answer: Focal plane.
Why correct: A plane containing the focus is called focal plane.
Why others wrong: Other planes are unrelated.