The Human Eye and the Colourful World – MCQs with Answers and Explanations
60 Topic-wise MCQs — The Human Eye and the Colourful World
Instructions: Each question has four options (A–D). Correct answer is shown with a brief explanation to clear the concept.
Topic 1 — Structure & Function of the Human Eye (Q1–10)
Q1.
Which part of the eye provides most of the eye's focusing power?Answer: B
The cornea, being a curved transparent surface, does most of the refraction when light enters the eye; the lens fine-tunes focus.
Q2.
The iris controls which of the following?Answer: B
The iris adjusts pupil size to regulate light intensity entering the eye.
Q3.
Which cells in the retina are responsible for colour vision?Answer: B
Cones function in bright light and detect colour; rods are for low-light vision without colour.
Q4.
The image formed on the retina is:Answer: C
Lens + cornea focus light to form a real, inverted image on the retina; the brain interprets it as upright.
Q5.
Accommodation refers to:Answer: B
Accommodation is adjusting lens shape via ciliary muscles to focus at different distances.
Q6.
The optic nerve carries signals to the:Answer: C
The optic nerve transmits electrical impulses from retina to the brain's visual cortex for interpretation.
Q7.
Which part maintains the shape of the eyeball and is filled with a jelly-like substance?Answer: B
The vitreous humour fills the posterior chamber and helps maintain eye shape.
Q8.
Which structure helps in protecting the eye by producing tears?Answer: A
Lacrimal glands secrete tears that lubricate and protect the eye surface.
Q9.
The black circular opening in the centre of the iris is called:Answer: B
The pupil is the aperture controlling light entry; its size is regulated by the iris.
Q10.
Which of the following is true about cones?Answer: C
Cones are concentrated in the fovea, enable colour vision and provide sharp central vision.
Topic 2 — Image Formation & Lens Formula (Q11–20)
Q11.
The lens formula is:Answer: B
Using sign convention in the form used by NCERT, 1/f = 1/v − 1/u is the standard lens relation.
Q12.
If an object is placed at infinity for a convex lens, where is the image formed?Answer: C
Parallel rays from infinity converge at the focal point f for a convex lens.
Q13.
Magnification m for a lens is given by:Answer: B
Linear magnification is ratio of image distance to object distance, m = v/u (or height ratio).
Q14.
For a convex lens, if object is at 2f, image distance will be:Answer: C
When object at 2f, image forms at 2f, same size and inverted.
Q15.
A lens of power +4 D has focal length equal to:Answer: B
Power P = 1/f (in metres) ⇒ f = 1/4 = 0.25 m or 25 cm.
Q16.
An image formed by a lens is magnified and inverted. The object is likely placed at:Answer: B
Object between f and 2f produces a real, inverted, magnified image located beyond 2f.
Q17.
When the object is within the focal length of a convex lens, the image is:Answer: C
Object inside f yields a virtual, erect, magnified image on the same side as the object.
Q18.
For a concave lens, image of a real object is always:Answer: B
Concave (diverging) lens forms virtual, erect, and diminished images for real objects.
Q19.
If u = −30 cm and v = 60 cm for a convex lens, the focal length f is:Answer: A
Using 1/f = 1/v −1/u = 1/60 − 1/(−30) = 1/60 +1/30 = (1+2)/60 = 3/60 ⇒ f = 20 cm.
Q20.
The sign of focal length for a concave lens is:Answer: B
By convention, concave (diverging) lenses have negative focal lengths.
Topic 3 — Defects of Vision & Their Correction (Q21–30)
Q21.
A person cannot see distant objects clearly but can see nearby objects. This condition is called:Answer: B
Myopia (short-sightedness) means distant objects are blurred; corrected with concave lenses.
Q22.
Which lens is used to correct hypermetropia?Answer: B
Hypermetropia is corrected with convex (converging) lenses which shift image onto retina.
Q23.
Presbyopia occurs mainly because of:Answer: C
Presbyopia is age-related and results from stiffening of the lens reducing accommodation.
Q24.
A person with myopia has a far point of 1.5 m. Power of corrective lens required for distant vision is approximately:Answer: B
For object at infinity, image should be at far point v = −1.5 m ⇒ f = −1.5 ⇒ P = −0.67 D.
Q25.
Cataract affects which part of the eye?Answer: B
Cataract is clouding of the eye's natural lens, treated by surgical replacement.
Q26.
Bifocal lenses are used to correct which condition?Answer: C
Bifocals have two powers to assist both near and distant vision, useful for presbyopia.
Q27.
Which of the following indicates correct spectacle prescription notation for a person needing a −2 D lens?Answer: C
Negative sign indicates diverging (concave) lens with power −2 dioptres for myopia.
Q28.
Which optical device replaces the cloudy natural lens in cataract surgery?Answer: B
Cataract surgery often implants an artificial intraocular lens to restore focus.
Q29.
The near point of a normal human eye is about:Answer: C
Typical near point for a young person with normal accommodation is ~25 cm.
Q30.
In myopia, the image of a distant object is formed:Answer: C
Myopia causes image to form in front of retina, making distant objects blurred.
Topic 4 — Dispersion, Prism & Spectrum (Q31–40)
Q31.
Dispersion of white light is caused by:Answer: C
Different wavelengths refract by different amounts due to variation of refractive index with wavelength.
Q32.
Order of colours in a visible spectrum from least to most deviated is:Answer: A
Red deviates least, violet most; sequence from least to most: Red, Orange, Yellow, Green, Blue, Indigo, Violet.
Q33.
Which of the following devices is best to spread white light into a spectrum on a screen?Answer: C
Prism shape causes angular dispersion producing a visible spectrum on a screen.
Q34.
Why does violet light bend more than red light in a prism?Answer: C
Higher refractive index for shorter wavelengths causes greater bending for violet.
Q35.
If white light is incident on a prism, which colour emerges closest to the base of the prism?Answer: D
Violet deviates the most and thus emerges closest to the prism base (most deviated side).
Q36.
Which phenomenon explains formation of colors in soap bubbles and thin films (different from prism dispersion)?Answer: B
Thin-film interference produces colourful patterns; different mechanism than prism dispersion.
Q37.
A student cannot see a spectrum when white light passes through a glass slab because:Answer: B
Parallel faces cause equal but opposite deviations leading to lateral shift without angular dispersion.
Q38.
Which of the following is NOT a property of colours obtained from dispersion of white light?Answer: C
Colours from dispersion depend on wavelength; the incorrect statement is that they are independent of wavelength.
Q39.
Which colour has the longest wavelength in the visible spectrum?Answer: D
Red has the longest wavelength (~700 nm) while violet is shortest (~400 nm).
Q40.
The separation of colours produced by a prism is called a:Answer: A
The dispersed colours form a spectrum; 'rainbow' is a natural spectrum formed by droplets.
Topic 5 — Scattering, Sky Colour & Rainbows (Q41–50)
Q41.
Rayleigh scattering intensity varies approximately as:Answer: D
Rayleigh scattering ∝ 1/λ^4, so shorter (blue) wavelengths scatter much more.
Q42.
Why does the sky appear red during sunrise/sunset?Answer: B
Longer path through atmosphere removes blue/green by scattering, so red reaches the observer.
Q43.
A primary rainbow forms roughly at an angle of about:Answer: B
Primary rainbow angle is about 42° from the antisolar point for red light.
Q44.
The secondary rainbow appears outside the primary and is fainter because:Answer: B
Two internal reflections reduce intensity and reverse colour order, making it fainter.
Q45.
The Tyndall effect is most closely related to which of the following?Answer: B
Tyndall effect is scattering by colloidal-sized particles, making light path visible.
Q46.
Why are clouds usually white?Answer: B
Cloud droplets are large relative to wavelength and scatter all visible wavelengths similarly (Mie scattering), producing white appearance.
Q47.
What is the primary cause of the blue colour of distant mountains observed from a valley?Answer: B
Atmospheric scattering of shorter wavelengths makes distant objects appear bluish and less saturated.
Q48.
During the day, the sun appears white because:Answer: B
Direct sunlight contains all visible wavelengths; although scattering removes some blue from the direct beam, the sun still appears white to the eye.
Q49.
Which scattering explains the blue colour of the clear daytime sky?Answer: C
Rayleigh scattering by small air molecules preferentially scatters shorter wavelengths such as blue.
Q50.
The angular radius of a primary rainbow is measured from the:Answer: B
Rainbow angles are measured from the antisolar point; primary red around 42° from this point.
Topic 6 — Colours of Objects, Practical & Diagrams (Q51–60)
Q51.
A red cloth appears black under green light because:Answer: A
Red cloth reflects red wavelengths; under green illumination there is little red to reflect, so it appears dark.
Q52.
Which statement is true about pigments and colours?Answer: C
Colours arise because materials reflect some wavelengths and absorb others; light source spectrum affects observed colour.
Q53.
In the lens practical, which ray passes through the optical centre without deviation?Answer: C
A ray through the optical centre of a thin lens goes straight without deviation (approximation).
Q54.
When drawing ray diagrams, dotted lines are used to represent:Answer: B
Dotted lines indicate the apparent extensions of rays (virtual rays) used to locate virtual images.
Q55.
In an optics experiment, why is it important to use a ray box with a narrow slit?Answer: C
A narrow slit produces narrow, well-defined rays necessary for precise ray diagrams and measurements.
Q56.
Which of the following should NOT be omitted when labeling a lens diagram in exams?Answer: D
All these labels are essential for clarity and to score method marks.
Q57.
The perceived colour of an object under coloured light depends on:Answer: C
Observed colour is determined by the light incident on the object and which wavelengths the object reflects.
Q58.
For a convex lens, if the object distance equals focal length (u = f), the image is formed at:Answer: C
Object at focal point makes refracted rays parallel; image is formed at infinity.
Q59.
Which practice improves accuracy when measuring focal length using a distant object?Answer: B
A distinct distant object acts like infinity and yields accurate focal length measurement when image is sharply focused on the screen.
Q60.
When light passes through a coloured glass filter, the transmitted light is:Answer: A
Coloured filters transmit certain wavelengths and absorb others, so transmitted light is enriched in the filter's colour.