Answer: When a ray of light enters a prism, it bends because of refraction of light. When the ray of light finally emerges out of the prism. it deviates drastically from its original path. This...
How can we explain the reddish appearance of the sun at sunrise or sunset? Why does it not appear red at noon?
Answer: The sun appears red at sunrise and sunset because the sun is closer to the horizon during these times of the year. During its journey to our eyes, sunlight passes through a denser layer of...
Explain the refraction of light through a triangular glass prism using a labelled ray diagram. Hence define the angle of deviation.
The refraction of light through a triangular glass prism is depicted in the illustration above. At the first surface AB, a beam of light PE is penetrating the glass from the surrounding air. Due to...
When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eye can be corrected?
Answer: Myopia is a condition in which a person's ability to see distant objects clearly is impaired. Myopia is a condition in which the image is created in front of the retina rather than behind...
Explain the structure and functioning of the human eye. How are we able to see nearby as well as distant objects?
Answer: The human eye is considered to be one of the most valuable and sensitive sense organs on the planet. It allows us to take in the beauty of the world and the colours that surround us. After...
What is the difference in colours of the Sun observed during sunrise/sunset and noon? Give an explanation for each.
Answer: The sun appears red at sunrise and sunset because the sun is closer to the horizon during these times of the year. During its journey to our eyes, sunlight passes through a denser layer of...
Why is the colour of the clear sky blue?
Answer: The colour blue is the one that scatters the most light in the visible spectrum, and it is the most intense. As a result, the blue colour is able to reach us and the sky appears to be blue.
Why do we see a rainbow in the sky only after rainfall?
Answer: Rainbows are generated by the dispersion of sunlight by microscopic water droplets in the atmosphere, which are present in the air. A rainbow is always generated in the opposite direction to...
Is the position of a star as seen by us its true position? Justify your answer.
Answer: When starlight enters the earth's atmosphere, it is subjected to constant refraction. Refraction happens in a material with a refractive index that is gradually changing. Starlight is...
Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also indicate the order of the colours of the spectrum obtained.
Solution: The ray diagram is:
How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.
Solution: Using two identical prisms that are inverted with regard to one another, we can create a narrow beam of white light that is incident on one prism and emerges out of the second prism as...
A person needs a lens of power –4.5 D for correction of her vision. (c) What is the nature of the corrective lens?
Answer: Myopia is a condition in which a pupil is unable to see the chalkboard that is far away from her. As a result, the doctor recommends a concave lens with a proper focal length. Negative sign...
A person needs a lens of power –4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
Solution: Myopia is a condition in which a pupil is unable to see the chalkboard that is far away from her. As a result, the doctor recommends a concave lens with a proper focal length. Answer is...
How are we able to see nearby and also the distant objects clearly?
Answer: By varying the focal length of the lens, we can make our eyes focus on images from a variety of different distances. The action of the Ciliary muscle aids in the adjustment of the focal...
A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.
Myopia is a condition in which a pupil is unable to see the chalkboard that is far away from her. As a result, the doctor recommends a concave lens with a proper focal length.
Draw ray diagrams each showing (i) myopic eye and (ii) hypermetropic eye.
Solution: Myopia is a condition in which a person's ability to see distant objects clearly outweighs his ability to perceive those closer to him. Hypermetropia is a condition in which a person...
Which of the following statement is correct?
(a) A person with myopia can see distant objects clearly
(b) A person with hypermetropia can see nearby objects clearly
(c) A person with myopia can see nearby objects clearly
(d) A person with hypermetropia cannot see distant objects clearly
Solution: Answer is (c) A person with myopia can see nearby objects clearly Myopia is a condition in which a person's ability to see distant objects clearly outweighs his ability to perceive those...
The focal length of the eye lens increases when eye muscles
(a) are relaxed and the lens becomes thinner
(b) contract and lens become thicker
(c) are relaxed and the lens becomes thicker
(d) contract and lens become thinner
Solution: Answer is (a) are relaxed and the lens becomes thinner When the eye muscles relax and become thinner, the focal length of the eye lens grows in proportion to its thickness. The retina is...
When light rays enter the eye, most of the refraction occurs at the
(a) crystalline lens
(b) outer surface of the cornea
(c) iris
(d) pupil
Solution: The answer is (b) the outer surface of the cornea The cornea is a thin membrane that allows light to pass through to the eye. When light rays strike the cornea, they are bent inward and...
The bluish colour of water in the deep sea is due to
(a) the presence of algae and other plants found in water
(b) reflection of sky in water
(c) scattering of light
(d) absorption of light by the sea
Solution: The answer is (b) reflection of sky in water Explanation: Water is colourless, but it takes on the colour of whatever it is reflected by. As a result, the sea seems blue.
Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?
(a) Dispersion of light
(b) Scattering of light
(c) Total internal reflection of light
(d) Reflection of light from the earth
Solution: The answer is (b) Scattering of light Explanation: Because red scatters the least amount of light, it may go a long distance. When the sun sets or rises, light has to travel a long...
The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light
(a) is scattered the most by smoke or fog
(b) is scattered the least by smoke or fog
(c) is absorbed the most by smoke or fog
(d) moves fastest in air
Solution: The answer is (b) is scattered the least by smoke or fog Because the wavelength of red colour is the longest, it may be seen clearly from a long distance. It is the colour that is least...
Which of the following statements is correct regarding the propagation of light of different colours of white light in air?
(a) Red light moves fastest
(b) Blue light moves faster than green light
(c) All the colours of the white light move with the same speed
(d) Yellow light moves with the mean speed as that of the red and the violet light
Solution: The correct option is C All of the colours in the white light travel at the same speed as one another. Because air is not a dispersive medium, light of all wavelengths travels at the same...
The clear sky appears blue because
(a) blue light gets absorbed in the atmosphere
(b) ultraviolet radiations are absorbed in the atmosphere
(c) violet and blue lights get scattered more than lights of all other colors by the atmosphere
(d) light of all other colors is scattered more than the violet and blue color lights by the atmosphere
Solution: Answer is (c) violet and blue lights get scattered more than lights of all other colors by the atmosphere. Rayleigh's scattering of sunlight is responsible for the blue appearance of the...
At noon the sun appears white as
(a) light is least scattered
b) all the colours of the white light are scattered away
(c) blue colour is scattered the most
(d) red colour is scattered the most
Solution: The answer is (b) all the colours of the white light are scattered away This is due to the dispersion of light caused by the presence of air in the environment.
Which of the following phenomena of light are involved in the formation of a rainbow?
(a) Reflection, refraction, and dispersion
(b) Refraction, dispersion, and total internal reflection
(c) Refraction, dispersion, and internal reflection
d) Dispersion, scattering and total internal reflection
Solution: Answer is (c) Refraction, dispersion, and internal reflection Dispersion of light results in the scattering of white light into multiple colours at different angles, resulting in internal...
A prism ABC (with BC as a base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in Figure 11.1. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky? The Human Eye and the Colourful World CHAPTER11 Fig.11.1
(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)
Solution: The answer is (b) (ii) If the prism is kept with BC at the bottom, a band of colour appears at the bottom that is violet. If the prism is kept with BC at the top, violet will be at the top...
A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct?
(a) The near point of his eyes has receded away
(b) The near point of his eyes has come closer to him
(c) The far point of his eyes has come closer to him
(d) The far point of his eyes has receded away
Solution: Answer is (a) The near point of his eyes has receded away In hypermetropia, the near spot of the eye is moved away for 25 cm. Thus, in order to read properly, the user needs maintain the...
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power
(a) + 0.5 D
(b) – 0.5 D
(c) + 0.2 D
(d) – 0.2 D
Solution:The answer is (b) – 0.5 D Because the individual is myopic and in need of a concave mirror, the power would be in the negative. P=1/f=1/2m=0.5 D.