1A group of students went for a picnic. One of them, Rohan, who normally wears spectacles to correct his vision, forgot to bring them. He found that he could see the trees and mountains far away quite clearly, but struggled to read the menu card brought close to him.(a) Identify the defect of vision Rohan is suffering from. [1 mark](b) Explain the defect with the help of a ray diagram showing image formation in his eye. [2 marks](c) Suggest the type of lens required to correct this defect and explain its role. 2marks
2Anshul is observing a colourful spectrum projected on a screen after passing white light through a prism. He notices that the colours are arranged in a specific order. He then tries to pass the spectrum through another identical prism placed in an inverted position.(a) Name the phenomenon responsible for splitting of white light into its constituent colours. [1 mark](b) What is the order of colours observed in the spectrum, starting from the top? [1 mark](c) What is the outcome of passing the spectrum through the second inverted prism? What does this demonstrate? 2marks
3A student observes that while watching a distant lighthouse, the light appears to flicker. However, when observing a nearby street lamp, the light appears steady.(a) Why do stars appear to twinkle, while planets do not? [3 marks](b) Explain the phenomenon responsible for the apparent twinkling of stars. 2marks
4Mrs. Sharma, a 60-year-old woman, is finding it difficult to read the newspaper, even when holding it at a normal reading distance of 25 cm. She also finds it hard to thread a needle.(a) Identify the vision defect Mrs. Sharma is likely suffering from. [1 mark](b) Explain the reason for the development of this defect. [2 marks](c) What type of lens would be required to correct this defect and why? 2marks
5Assertion (A): The sky appears blue during the day.Reason (R): Blue light is scattered more effectively than red light by the fine particles in the atmosphere. 1mark
6A beam of light composed of several colours passes through a glass prism and separates into its constituent colours. The colours obtained are arranged in a band on a screen.(a) Name the phenomenon observed. [1 mark](b) Name the colour which bends the least and the colour which bends the most. [1 mark](c) If another identical prism is placed in an inverted position behind the first prism, what will be observed? Explain. 3marks
7A group of students is performing an experiment with a glass prism. They observe that when white light passes through the prism, it splits into different colours.(a) Name the phenomenon shown in the experiment. [1 mark](b) List the colours in the order of their deviation from the incident ray. [1 mark](c) Explain why different colours deviate by different angles. 2marks
8A person finds it difficult to see objects beyond 2 metres clearly. The far point of their eye is 2 metres.(a) Identify the defect of vision. [1 mark](b) Calculate the power of the lens required to correct this defect. 3marks
9Assertion (A): The Sun appears reddish during sunrise and sunset.Reason (R): The red light has a longer wavelength and is scattered less by the atmospheric particles. 1mark
10A school student, sitting in the last row of the classroom, is unable to read the writing on the blackboard clearly. However, they can see objects at the back of the classroom quite well.(a) Identify the defect of vision the student is likely suffering from. [1 mark](b) Explain why this defect occurs, referring to the image formation in the eye. [2 marks](c) Name the type of lens that can be used to correct this defect and explain its working with a ray diagram. 3marks
11Observe the diagram below which illustrates a phenomenon in nature:(Imagine a diagram showing sunlight passing through raindrops, with dispersion and internal reflection, resulting in a rainbow.)(a) Identify the phenomenon illustrated in the diagram. [1 mark](b) List the optical phenomena involved in the formation of this natural display. [1 mark](c) Explain the role of water droplets in forming this phenomenon. 3marks
12Assertion (A): Planets do not twinkle, while stars do.Reason (R): Planets are much closer to the Earth and act as extended sources of light. 1mark
13A farmer notices that his crops are not growing well due to a lack of clear vision to inspect them from a distance. He can see nearby objects clearly but distant objects appear blurred.(a) Name the defect of vision the farmer is suffering from. [1 mark](b) Explain the cause of this defect. [2 marks](c) Suggest the type of corrective lens needed and briefly explain how it helps. 2marks
14A scientist is studying the properties of light. He passes white light through a prism and observes a band of colours. He then passes this band of colours through another inverted prism and observes that white light is formed.(a) What is the name of the phenomenon where white light splits into constituent colours? [1 mark](b) What is the name of the phenomenon where the constituent colours recombine to form white light? [1 mark](c) Explain why different colours bend by different amounts when passing through a prism. 3marks
15A photographer is adjusting his camera lens to capture a clear image of a distant landscape and then a close-up of a flower. The camera lens, like the human eye, adjusts its focal length.(a) What is the biological term for the ability of the human eye to adjust its focal length for clear vision of objects at different distances? [1 mark](b) Explain how this adjustment occurs in the human eye. [2 marks](c) What is the minimum distance at which a normal human eye can see objects distinctly without strain? 1mark
16Assertion (A): When viewed through a prism, the colour of light that bends the least is red.Reason (R): The angle of deviation is inversely proportional to the wavelength of light. 1mark
17A space tourist is looking out of the window of the spacecraft at the Earth's atmosphere. They observe that the sky appears black.(a) Explain why the sky appears black from a very high altitude. [2 marks](b) Explain why the sky appears blue when viewed from the Earth's surface. 2marks
18A student accidentally spills some ink on a textbook, making it difficult to read. The student moves the book closer to their eyes to read the text.(a) If the student can read the text comfortably, what can be inferred about their vision? [1 mark](b) If the student is unable to read the text even when holding it very close (less than 25 cm), what vision defect might they have? [1 mark](c) What is the minimum distance at which a normal eye can see an object distinctly? 1mark
19Mr. Gupta, an elderly gentleman, is finding it difficult to see the menu at a restaurant, even with good lighting. He can see the distant decorations clearly but struggles with the menu card.(a) Name the defect Mr. Gupta is suffering from. [1 mark](b) Explain the cause of this defect. [2 marks](c) What type of lens is required to correct this defect? 1mark
20A teacher is demonstrating the refraction of light through a prism. White light enters the prism and splits into seven colours.(a) Name the phenomenon demonstrated. [1 mark](b) State the colour that deviates the least and the colour that deviates the most. [1 mark](c) Explain the reason for the different deviations of different colours. 3marks
Answers
1.(a) Hypermetropia (far-sightedness). [1 mark](b) In hypermetropia, the image of a nearby object is focused behind the retina. This is because either the focal length of the eye lens is too long or the eyeball has become too short. The ray diagram would show parallel rays from a nearby object entering the eye and converging behind the retina. [2 marks](c) A convex lens of appropriate power is required. A convex lens is a converging lens. It adds to the converging power of the eye lens, causing the rays from a nearby object to converge on the retina. 2marks
2.
(a) Dispersion of light. [1 mark]
(b) Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR). [1 mark]
(c) White light will be obtained. This demonstrates the recombination of the spectrum of white light, proving that white light is composed of seven colours. [2 marks]
3.
(a) Stars are very distant point-sized sources of light. As their light rays travel through the Earth's atmosphere, they undergo continuous refraction due to varying refractive indices. This causes the apparent position of the star to fluctuate slightly, leading to twinkling. Planets are closer to Earth and act as extended sources. The light from different parts of the planet averages out, cancelling the twinkling effect. [3 marks]
(b) Atmospheric refraction of starlight. The variation in the refractive index of atmospheric layers causes the starlight to bend differently from moment to moment, making the star appear to flicker. [2 marks]
4.
(a) Presbyopia. [1 mark]
(b) Presbyopia typically occurs with age due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens. This reduces the eye's ability to accommodate and focus on nearby objects. [2 marks]
(c) A convex lens is required. The convex lens adds converging power to the eye lens, enabling it to focus on nearby objects clearly. [2 marks]
5(A) Assertion (A): The sky appears blue during the day.(R) Reason (R): Blue light is scattered more effectively than red light by the fine particles in the atmosphere. 1mark
6.
(a) Dispersion of white light. [1 mark]
(b) Red light bends the least, and violet light bends the most. [1 mark]
(c) White light will emerge from the second prism. This demonstrates that the white light incident on the first prism was split into its constituent colours, and the second prism recombines these colours to form white light again. [3 marks]
7.
(a) Dispersion of white light. [1 mark]
(b) Red, Orange, Yellow, Green, Blue, Indigo, Violet (Red bends the least, Violet bends the most). [1 mark]
(c) The refractive index of the prism material is slightly different for different wavelengths (colours) of light. Shorter wavelengths (like violet) are refracted more than longer wavelengths (like red). This causes different colours to bend by different angles. [2 marks]
8.
(a) Myopia (near-sightedness). [1 mark]
(b) The far point of the myopic eye is 2 m. To see distant objects clearly, the eye needs to focus them at infinity. The corrective lens should form a virtual image of an object at infinity at the far point (2 m). This means the lens must form an image at 2 m of an object at infinity.
Using lens formula:
Here, , m (image is virtual and formed on the same side as object).
So, the focal length m.
The power of the lens is D. [3 marks]
9(A) Assertion (A): The Sun appears reddish during sunrise and sunset.(R) Reason (R): The red light has a longer wavelength and is scattered less by the atmospheric particles. 1mark
10.
(a) Myopia (near-sightedness). [1 mark]
(b) In myopia, the eyeball is often too long or the power of the eye lens is too high. This causes the image of a distant object to be focused in front of the retina, instead of on the retina. [2 marks]
(c) A concave lens is used. A concave lens diverges the parallel rays from a distant object before they enter the eye. This allows the eye lens to focus the image on the retina. The ray diagram shows parallel rays incident on a concave lens, then entering the eye and converging on the retina. [3 marks]
11.
(a) Formation of a rainbow. [1 mark]
(b) Refraction, dispersion, and internal reflection. [1 mark]
(c) When sunlight enters a raindrop, it is refracted and dispersed into its constituent colours. These colours then undergo total internal reflection at the back surface of the raindrop and are refracted again as they emerge from the raindrop. This combination of phenomena creates the spectrum of colours we see as a rainbow. [3 marks]
12(A) Assertion (A): Planets do not twinkle, while stars do.(R) Reason (R): Planets are much closer to the Earth and act as extended sources of light. 1mark
13.
(a) Hypermetropia (far-sightedness). [1 mark]
(b) This defect occurs because the focal length of the eye lens is too long, or the eyeball is too short. As a result, light rays from nearby objects are focused behind the retina. [2 marks]
(c) A convex lens is required. A convex lens converges the light rays before they enter the eye, effectively increasing the converging power of the eye lens and ensuring the image is formed on the retina. [2 marks]
14.
(a) Dispersion of white light. [1 mark]
(b) Recombination of spectrum of white light. [1 mark]
(c) The refractive index of the prism material is different for different colours (wavelengths) of light. This phenomenon is called dispersion. Violet light (shorter wavelength) has a higher refractive index and hence bends more, while red light (longer wavelength) has a lower refractive index and bends less. [3 marks]
15.
(a) Accommodation. [1 mark]
(b) The ciliary muscles contract or relax to change the curvature of the eye lens. When focusing on distant objects, the ciliary muscles relax, making the lens thinner and increasing its focal length. When focusing on nearby objects, the ciliary muscles contract, making the lens thicker and decreasing its focal length. [2 marks]
(c) 25 cm. [1 mark]
16(A) Assertion (A): When viewed through a prism, the colour of light that bends the least is red.(R) Reason (R): The angle of deviation is inversely proportional to the wavelength of light. 1mark
17.
(a) From very high altitudes, there are very few atmospheric particles to scatter sunlight. Hence, scattering is negligible, and the sky appears black, similar to how it appears in space. [2 marks]
(b) The blue colour of the sky is due to the scattering of sunlight by the tiny molecules of air in the atmosphere. Blue light has a shorter wavelength and is scattered more strongly than red light (longer wavelength). This scattered blue light reaches our eyes from all directions, making the sky appear blue. [2 marks]
18.
(a) The student might have hypermetropia (far-sightedness) or presbyopia, as they can see distant objects clearly but struggle with nearby ones. [1 mark]
(b) If the student cannot read text even at very close distances (less than 25 cm), they might be suffering from severe hypermetropia or presbyopia, where the eye's ability to accommodate is significantly reduced. [1 mark]
(c) 25 cm. [1 mark]
19.
(a) Presbyopia. [1 mark]
(b) Presbyopia is an age-related condition. It occurs due to the weakening of the ciliary muscles and the decreased elasticity of the eye lens, which reduces the eye's ability to adjust its focal length to see nearby objects clearly. [2 marks]
(c) A convex lens. [1 mark]
20.
(a) Dispersion of white light by a prism. [1 mark]
(b) Red light deviates the least, and violet light deviates the most. [1 mark]
(c) The refractive index of the prism material varies for different wavelengths (colours) of light. Shorter wavelengths (like violet) experience a higher refractive index and thus greater deviation, while longer wavelengths (like red) experience a lower refractive index and thus less deviation. [3 marks]
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