Human Eye & Colourful World CBQs — CBSE Class 10 (2027) with step-wise solutions

Sample Human Eye & Colourful World CBQs

1. Question 1MCQ1 mark
   Under which of these can myopia and hypermetropia be classified?
   • breakdown of tissues
   • incorrect bending of light in the eye
   • incorrect reflection of light by surfaces around us
   • incorrect coordination with brain for colour
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   1. [1 mark] Correct option: (2) incorrect bending of light in the eye. Both are refractive defects - the eye's converging power does not match its length, so light is not bent to focus on the retina.

   Answer: incorrect bending of light in the eye

2. Question 2Assertion-Reason1 mark
   Assertion (A): When a doctor shines a bright torch into a patient's eye, the patient's pupil becomes smaller within a moment. Reason (R): The ciliary muscles contract to reduce the size of the pupil when bright light falls on the eye.
   • (A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
   • (B) Both Assertion and Reason are true but Reason is NOT the correct explanation of Assertion.
   • (C) Assertion is true but Reason is false.
   • (D) Assertion is false but Reason is true.
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   1. [1 mark] (C): A is true, since in bright light the pupil contracts to limit the light reaching the retina. R is false, because the size of the pupil is controlled by the iris; the ciliary muscles change the curvature of the eye lens.

   Answer: (C) Assertion is true but Reason is false.

3. Question 3Short answer2 marks
   Space is mostly vacuum, devoid of any medium. (a) What colour does the Sun appear to the astronauts on International Space Station? (b) Give reason for your answer to (a).
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   1. [1 mark] (a) white
   2. [1 mark] (b) Since there is no medium to disperse or scatter the light coming from the Sun, it appears white.

   Answer: (a) white; (b) there is no medium in space to scatter or disperse the sunlight.

4. Question 4Case study4 marks
   Neha, a student in Dehradun, darkened her room and let a narrow beam of sunlight enter through a slit in a thick curtain. She placed a glass prism in the path of the beam and turned it slowly until a band of seven colours appeared on the white wall. She noted that the colours appeared in the order violet, indigo, blue, green, yellow, orange and red, and that the different colours were bent through different angles. Next, she switched off the sunlight and sent the light of a red laser pointer through the same prism. This time she saw only a single red spot on the wall, a little away from the straight path of the beam. (i) Which colour of the band is bent the most by the prism? (ii) Why did the red laser light not form a band of colours? (iii) Explain why white light splits into its component colours on passing through a glass prism.
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   1. [1 mark] (i) Violet light is bent (deviated) the most.
   2. [1 mark] (ii) The red laser light is of a single colour (monochromatic); it does not contain other colours, so the prism only deviates it and does not split it into a band.
   3. [1 mark] (iii) White light is a mixture of seven colours; on entering the glass prism the different colours travel at different speeds, so each colour bends through a different angle with respect to the incident ray.
   4. [1 mark] (iii) Red light bends the least and violet the most, so the colours come out of the prism along different paths and separate into a band — this is dispersion.

   Answer: (i) Violet; (ii) red laser light is a single colour, so it is only deviated, not split; (iii) the colours of white light travel at different speeds in glass and bend through different angles (red least, violet most), so they separate — dispersion.

5. Question 5Long answer5 marks
   A 16-year-old student in Jaipur cannot see objects clearly beyond 80 cm from her eyes, though she can read a book comfortably. (a) Name the defect of vision she is suffering from. Where is the image of a distant object formed in her eye? (b) List two possible causes of this defect. (c) Name the type of lens needed to correct her vision and find its focal length. (d) Calculate the power of the corrective lens. (e) How is a normal eye able to see clearly both a distant tree and a book held at 25 cm?
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   1. [1 mark] (a) Myopia (near-sightedness); the image of a distant object is formed in front of the retina instead of on it.
   2. [1 mark] (b) (1) Excessive curvature of the eye lens; (2) elongation of the eyeball.
   3. [1 mark] (c) A concave (diverging) lens, which forms a virtual image of a distant object at her far point: u = −∞, v = −80 cm, so 1/f = 1/v − 1/u = −1/80 ⇒ f = −80 cm = −0.8 m.
   4. [1 mark] (d) P = 1/f (in m) = 1/(−0.8) = −1.25 D.
   5. [1 mark] (e) By the power of accommodation: the ciliary muscles change the curvature, and hence the focal length, of the eye lens — they relax (lens thinner, longer focal length) for the distant tree and contract (lens thicker, shorter focal length) for the book.

   Answer: (a) Myopia, image in front of the retina; (b) excessive lens curvature, elongated eyeball; (c) concave lens, f = −80 cm; (d) −1.25 D; (e) power of accommodation by the ciliary muscles.

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