Class 10 The Human Eye and the Colourful World Mock Test (CBSE)

Topics in The Human Eye and the Colourful World

• The human eye
• Power of accommodation
• Defects of vision and their correction
• Refraction of light through a prism
• Dispersion of white light by a glass prism
• Atmospheric refraction
• Scattering of light
• Tyndall effect
• Why the clear sky is blue

The Human Eye and the Colourful World practice questions with answers

1. Q1Assertion and reason·1 mark
   Assertion (A): The sky appears blue on a clear day. Reason (R): Air molecules are much smaller than the wavelength of visible light, so they scatter shorter wavelengths like blue light more strongly than longer wavelengths like red light.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   A student sitting on the last bench of a classroom can read the blackboard clearly but struggles to read text written in a textbook kept on the desk. Identify the defect of vision and the appropriate corrective lens needed.

   1. (a)Hypermetropia, corrected by a convex lens
   2. (b)Myopia, corrected by a convex lens
   3. (c)Myopia, corrected by a concave lens
   4. (d)Presbyopia, corrected by a bifocal lens
   Show answer and step marks

   1. Correct option: (a) The student can see distant objects clearly but has trouble seeing nearby objects, which is the characteristic defect of hypermetropia (far-sightedness). It is corrected by using a convex lens.+1

   Answer: (a)
3. Q3Multiple choice·1 mark
   Water droplets in clouds are much bigger than the molecules of air. Compared with the scattering of light by fine air molecules, the scattering of white light by these water droplets is such that:

   1. (a)they scatter blue light much more strongly than red light
   2. (b)they scatter red light much more strongly than blue light
   3. (c)they scatter all colours of white light almost equally
   4. (d)they do not scatter light at all
   Show answer and step marks

   1. Correct option: (c) they scatter all colours of white light almost equally+1

   Answer: (c)
4. Q4Multiple choice·1 mark
   When a ray of light passes through a glass prism, it suffers refraction at both the refracting surfaces. The emergent ray bends:

   1. (a)parallel to the incident ray
   2. (b)away from the base of the prism
   3. (c)towards the base of the prism
   4. (d)perpendicular to the incident ray
   Show answer and step marks

   1. Correct option: (c) towards the base of the prism+1

   Answer: (c)
5. Q5Multiple choice·1 mark
   When a beam of light passes through a colloidal solution such as starch in water, its path becomes visible when viewed from the side. This phenomenon is called:

   1. (a)dispersion of light
   2. (b)total internal reflection
   3. (c)atmospheric refraction
   4. (d)Tyndall effect
   Show answer and step marks

   1. Correct option: (d) Tyndall effect+1

   Answer: (d)
6. Q6Long answer·5 marks
   Ravi can read distant road signs clearly, but when he holds a book at $25\text{ cm}$ from his eyes, the letters look blurred. On testing, his eye specialist finds that the nearest point at which he can see objects clearly, without any correction, is $50\text{ cm}$ from his eye. (a) Name the defect of vision from which Ravi suffers. [1] (b) Explain why his eye cannot focus the image of the book, held at $25\text{ cm}$, on the retina. [2] (c) Calculate the power of the lens required to correct his vision so that he can read the book held at $25\text{ cm}$ clearly. Assume the lens is placed close to the eye. [2]
   Show answer and step marks

   1. (a) Hypermetropia (long-sightedness)+1
   2. (b) For a near object, the image is formed behind the retina because the eye lens cannot converge the rays enough.+1
   3. (b) This happens because the focal length of the eye lens is too long for the near object, since the eyeball is too short or the eye lens is too flat.+1
   4. (c) For the corrective lens, $u = -25\text{ cm}$ and the virtual image must be at the near point, $v = -50\text{ cm}$. Using $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$ gives $\frac{1}{f} = -\frac{1}{50} + \frac{1}{25} = \frac{1}{50}\text{ cm}^{-1}$.+1
   5. $f = +50\text{ cm} = +0.5\text{ m}$, so the lens is convex.+0.5
   6. Power $P = \frac{1}{f} = \frac{1}{0.5} = +2\text{ D}$+0.5

   Answer: (a) Hypermetropia (long-sightedness). (b) The image of an object at $25\text{ cm}$ is formed behind the retina, as the eye lens cannot converge the rays enough. (c) $P = +2\text{ D}$ (convex lens, $f = +0.5$ m)

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