📘 Human Eye and Colourful World – MCQs (Class 10 Science)

🔹 Part 2: Questions 26–50

Q26. The ciliary muscles of human eye are responsible for:

A) Producing tears
B) Controlling pupil size
C) Changing focal length of eye lens
D) Protecting the eye from dust

Correct Answer: C) Changing focal length of eye lens

Explanation:

• A) Producing tears → Lacrimal glands.
• B) Controlling pupil size → Iris.
• ✅ C) Ciliary muscles → Contract/relax to change lens curvature (accommodation).
• D) Eyelids/eyelashes → Dust protection.

Q27. The focal length of human eye lens is controlled by:

A) Retina
B) Iris
C) Ciliary muscles
D) Cornea

Correct Answer: C) Ciliary muscles

Explanation:

• ✅ C) Adjusts curvature of lens.
• A, B, D → Other functions.

Q28. The near point of a person suffering from hypermetropia is:

A) Less than 25 cm
B) More than 25 cm
C) At 25 cm
D) At infinity

Correct Answer: B) More than 25 cm

Explanation:

• ✅ B) Hypermetropic person → Cannot see near objects clearly, near point shifts beyond 25 cm.

Q29. The focal length of normal human eye lens in relaxed state is about:

A) 1 cm
B) 2.5 cm
C) 4 cm
D) 10 cm

Correct Answer: B) 2.5 cm

Explanation:

• ✅ B) Approx. 2.5 cm in normal condition.
• Others → Wrong values.

Q30. Which eye defect requires bifocal lens for correction?

A) Myopia
B) Hypermetropia
C) Presbyopia
D) Astigmatism

Correct Answer: C) Presbyopia

Explanation:

• ✅ C) Presbyopia → Near and distant vision both affected → Bifocals used.

Q31. A person can see objects only beyond 1 m clearly. His eye defect is:

A) Hypermetropia
B) Myopia
C) Presbyopia
D) Astigmatism

Correct Answer: B) Myopia

Explanation:

• ✅ B) Myopia → Cannot see far objects clearly.
• A) Hypermetropia → Cannot see near objects.

Q32. Which of the following is a natural phenomenon of dispersion?

A) Rainbow formation
B) Mirage
C) Twinkling of stars
D) Advance sunrise

Correct Answer: A) Rainbow formation

Explanation:

• ✅ A) Rainbow → Dispersion, reflection, refraction in raindrops.

Q33. Which optical phenomenon is responsible for advance sunrise and delayed sunset?

A) Reflection
B) Refraction
C) Dispersion
D) Scattering

Correct Answer: B) Refraction

Explanation:

• ✅ B) Atmospheric refraction bends sunlight → Sun visible even when below horizon.

Q34. The blind spot in the human eye is the region:

A) Where no image forms
B) With maximum cone cells
C) With maximum rod cells
D) For colour vision

Correct Answer: A) Where no image forms

Explanation:

• ✅ A) Optic nerve leaves eye, no photoreceptor cells → No image formed.

Q35. The persistence of vision enables us to see motion in cinema because:

A) Eyes can detect 25 frames/s
B) Eye lens magnifies images
C) Retina stores image for 1 second
D) Refraction occurs in eye

Correct Answer: A) Eyes can detect 25 frames/s

Explanation:

• ✅ A) Eye retains image for 1/16 s → Frames shown fast appear continuous.

Q36. Which of the following is responsible for twinkling of stars?

A) Reflection
B) Refraction through atmosphere
C) Dispersion
D) Scattering

Correct Answer: B) Refraction through atmosphere

Explanation:

• ✅ B) Changing density of air → Refraction varies → Apparent flickering.

Q37. Which of the following is not due to atmospheric refraction?

A) Advance sunrise
B) Twinkling of stars
C) Blue colour of sky
D) Apparent position of stars

Correct Answer: C) Blue colour of sky

Explanation:

• ✅ C) Blue colour → Due to scattering, not refraction.

Q38. The colour of sky appears blue due to:

A) Dispersion
B) Scattering of shorter wavelength light
C) Reflection of sea
D) Refraction

Correct Answer: B) Scattering of shorter wavelength light

Explanation:

• ✅ B) Rayleigh scattering ∝ 1/λ⁴ → Blue scattered most.

Q39. The danger signal lights are red because:

A) Red is attractive
B) Red has shortest wavelength
C) Red is least scattered
D) Red is invisible in day

Correct Answer: C) Red is least scattered

Explanation:

• ✅ C) Red has longest wavelength, least scattered → Visible from far.

Q40. The rainbow is formed due to:

A) Reflection only
B) Refraction and dispersion
C) Refraction, dispersion and internal reflection
D) Only scattering

Correct Answer: C) Refraction, dispersion and internal reflection

Explanation:

• ✅ C) All three combine to form rainbow in raindrops.

Q41. The splitting of white light into seven colours is due to:

A) Equal bending of all colours
B) Unequal bending of different colours
C) Reflection at surface
D) Absorption of colours

Correct Answer: B) Unequal bending of different colours

Explanation:

• ✅ B) Violet deviates most, red least → Dispersion.

Q42. In a prism, which colour deviates maximum?

A) Red
B) Green
C) Yellow
D) Violet

Correct Answer: D) Violet

Explanation:

• ✅ D) Violet → Shortest wavelength → Most deviation.

Q43. The phenomenon of mirage is due to:

A) Reflection of light
B) Refraction and total internal reflection
C) Dispersion
D) Scattering

Correct Answer: B) Refraction and total internal reflection

Explanation:

• ✅ B) Hot air near ground → Light bends/TIR → Mirage.

Q44. The splitting of sunlight into seven colours by raindrops is called:

A) Reflection
B) Refraction
C) Dispersion
D) Diffraction

Correct Answer: C) Dispersion

Explanation:

• ✅ C) Dispersion due to different refractive indices.

Q45. Which of the following phenomena explains red colour of Sun at sunset?

A) Dispersion
B) Scattering
C) Reflection
D) Refraction

Correct Answer: B) Scattering

Explanation:

• ✅ B) Blue scattered away, red (long λ) reaches eyes.

Q46. The twinkling of stars is absent in planets because:

A) Planets are closer and appear as extended sources
B) Planets emit no light
C) Planets do not undergo refraction
D) Planets are much larger

Correct Answer: A) Planets are closer and appear as extended sources

Explanation:

• ✅ A) Extended sources → Effects of refraction average out.

Q47. Which of the following phenomena makes the Sun appear reddish at sunrise and sunset?

A) Refraction
B) Dispersion
C) Scattering of shorter wavelengths away
D) Reflection

Correct Answer: C) Scattering of shorter wavelengths away

Explanation:

• ✅ C) Blue scattered away, red remains.

Q48. The spectrum produced by prism is an example of:

A) Regular reflection
B) Dispersion
C) Diffraction
D) Interference

Correct Answer: B) Dispersion

Explanation:

• ✅ B) Splitting into VIBGYOR → Dispersion.

Q49. Which part of the eye forms the image?

A) Cornea
B) Retina
C) Lens
D) Pupil

Correct Answer: B) Retina

Explanation:

• A) Cornea → Refraction only.
• B) ✅ Retina → Light-sensitive layer, image forms here.
• C) Lens → Focuses light.
• D) Pupil → Regulates light entry.

Q50. The colour of sky appears dark to astronauts because:

A) No scattering in absence of atmosphere
B) Dispersion of light in space
C) No refraction in space
D) No light in space

Correct Answer: A) No scattering in absence of atmosphere

Explanation:

• ✅ A) Space has no atmosphere → No scattering → Sky dark.

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