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प्रश्न
Explain how the formation of a rainbow occurs.
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उत्तर
(i) The formation of a rainbow in the sky is a combined result of refraction, dispersion and reflection of sunlight by water droplets present in the atmosphere after it has rained.
(ii) Sunlight is a mixture of seven colours: Violet, indigo, blue, green, yellow, orange and red. After it has stopped raining, the atmosphere contains a large number of water droplets. When sunlight is incident on a water droplet, there is
- Refraction and dispersion of light as it passes from air to water
- Internal reflection of light inside the droplet
- Refraction of light as it passes from water to air
(iii) The refractive index of water is different for different colours, being maximum for violet and minimum for red. Hence, there is dispersion of light (separation into different colours) as it passes from air to water.
(iv) The combined action of different water droplets (acting like tiny prisms) produces a rainbow with red colour on the outer side and violet colour on the inner side. The remaining five colours lie between these two colours. The rainbow is seen when the Sun is behind the observer and the water droplets are in the front.
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संबंधित प्रश्न
Write a short note on dispersion of light.
Write a relationship between the angle of incidence and angle of refractions for a given pair of media
Name a prism required for obtaining a spectrum of Ultraviolet light.
How can you bend light away from the normal?
Draw diagrams to show the refraction of light from
- air to glass, and
- glass to air. In each diagram, label the incident ray, refracted ray, the angle of incidence
- and the angle of refraction (r).
A monochromatic ray of light passes from air to glass. The wavelength of light in air is λ, the speed of light in air is c and in glass is V. If the absolute refractive index of glass is 1.5, write down
- the relationship between c and V,
- the wavelength of light in glass.
With the help of diagram of the principal section of a prism, indicate its refracting surfaces, refracting edge and base.
How does the angle of minimum deviation produces by a prism change with increase in :
the refracting angle of prism?
An object is viewed through a glass prism with its vertex pointing upwards. It appears to be displaced upward. Explain the reason.
Fig 4.31 below shows a light ray of single colour incident normally on two prisms A and B. In each case draw the path of the ray of light as it enters and emerges out of the prism. Mark the angle wherever necessary.
A coin is places at the bottom of a beaker containing water (refractive index = 4/3) to a depth of 12 cm. By what height the coin appears to be raised when seen from vertically above?
Which of the following is the best experimental set-up out of the four shown for tracing the path of a ray of light passing through a rectangular glass slab ?
While performing the experiment on tracing the path of a ray of light through a rectangular glass slab, in which of the following experimental set-ups is a student likely to get best results? P1 and P2 are the positions of pins fixed by him.
(A) I
(B) II
(C) III
(D) IV
A ray of light passes from air to water. In fig. 39, which of the ray A, B, C and D is the correct refracted ray?
In the fig. name the ray which represents the correct path of light while passing through a glass block.
Fill in the blank to complete the following sentence:
When light travels from a rarer to a denser medium, it bends ...........
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(a) Complete the path of the ray through the block.
(b) In the diagram, mark the angle of incidence (i) and the angle of refraction (r) at the first interface. How is the refractive index of glass related to the angles I and r?
(c) Mark angle of emergence by the letter e. How are the angles i and e related?
(d) Which two rays are parallel to each other? Name them.
(e) Indicate in the diagram the lateral displacement between the emergent ray and the incident ray.
Make the correct for each of the following :
With reference to the fig, the refractive index of the glass block is
Draw a ray diagram showing the lateral displacement of a ray of light when it passes through a parallel sided glass slab.
Choose the correct alternative and rewrite the following:
A glass slab is placed in the path of convergent light. The point of convergence of light
A glass slab is placed over a page on which the word VIBGYOR is printed with each letter in its corresponding colour.
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- If not, the state which letter will be raised to the maximum. Give a reason for your answer.
What should be the ratio of the speed of light through the liquid to the speed through the glass so that there is no refraction of light at the boundaries of the glass block when the system is illuminated by the light of one colour?
Define the term refractive index of a medium in terms of velocity of light.
Express the refractive index μ of a medium in terms of the velocity of light.
Name two instruments of the total refracting prism in which is used.
Draw ray of light bending towards the normal while passing from glass to water. Label your diagrams.
The figure shows two prisms A and B. A monochromatic ray of light PO is incident at the face of the prism A. Complete the diagram to show the path of the ray till it emerges out of the prism B.
How does the angle of deviation produced by a prism depend on the angle of incidence of light at the prism surface? Draw a graph to illustrate your answer.
Two parallel rays of Red and Violet travelling through the air, meet the air-glass boundary as shown in the above figure. Will their paths inside the glass be parallel? Give a reason for your answer.
Light passes through a rectangular glass slab and through a triangular glass prism. In what way does the direction of the two emergent beams differ and why?
Trace a ray of light incident at 30° on a surface if travelling from air to glass. What is the angle of refraction in this case? (R.I. for glass = 3/2).
The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as A, B, C and D in the figure. Which one of them is correct?
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 |
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| A | B | C | D |
Observe the figure and name the ray AB, ray CD, ray GH.
