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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
When a ray of light travels from air to glass slab and strikes the surface of separation at 90°, then it …………….
(a) bends towards normal
(b) bends away from normal
(c) passes unbent
(d) passes in zigzag way
What is a spectrum?
Define refraction and state the laws of refraction.
A student traces the path of a ray of light through a rectangular glass slab for the different values of angle of incidence. He observes all possible precautions at each step of the experiment. At the end of the experiment, on analyzing the measurements, which of the following conclusions is he likely to draw?
(A) ∠i = ∠e < ∠r
(B) ∠i < ∠e < ∠r
(C) ∠i > ∠e > ∠r
(D) ∠i = ∠e > ∠r
After tracing the path of a ray of light passing through a rectangular glass slab for four different values of the angle of incidence, a student reported his observations in tabular form as given below:
| S.No | ∠ i | ∠ r | ∠ e |
| I | 30° | 19° | 29° |
| II | 40° | 28° | 40° |
| III | 50° | 36° | 50° |
| IV | 60° | 40° | 59° |
The best observation is
(A) I
(B) II
(C) III
(D) IV
In your laboratory you trace the path of light rays through a glass slab for different values of angle of incidence (∠i) and in each case measure the values of the corresponding angle of refraction (∠r) and angle of emergence (∠e). On the basis of your observations your correct conclusion is:
(a) ∠i is more than ∠r, but nearly equal to ∠e
(b) ∠i is less then ∠r, but nearly equal to ∠e
(c) ∠i is more than ∠e, but nearly equal to ∠r
(d) ∠i is less than ∠e, but nearly equal to ∠r
Select from the following the best experimental setup for tracing the path of a ray of light passing through a rectangular glass slab.
(a) P
(b) Q
(c) R
(d) S
Study the following four experimental set-ups I, II, III and IV for the experiment, "To trace the path of a ray of light through a rectangular glass slab."
Which of the marked set-ups is likely to give best results (P1 and P2 are the positions of pins fixed on the incident ray)?
(A) I
(B) II
(C) III
(D) IV
Draw the diagram given below and clearly show the path taken by the emergent ray.
A ray of light passes from water to air. How does the speed of light change?
The following diagram shows a 60°, 30°, 90° glass prism of critical angle 42°, Copy the diagram and complete the path of incident ray AB emerging out of the prism marking the angle of incidence on each surface.
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).
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?
Name the colour of white light which is deviated the most on passing through a prism.
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?
The refractive index of glass is 1.5. From a point P inside a glass block, draw rays PA, PB and PC incident on the glass air surface at an angle of incidence 30°, 42° and 60° respectively.
- In the diagram show the approximate direction of these rays as they emerge out of the block.
- What is the angle of refraction for the ray PB?
`("Take" sin 42° =2/3)`
Select from the following the best experimental set-up for tracing the path of a ray of light through a glass slab:
(A) I
(B) II
(C) III
(D) IV
“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw labelled ray diagram to justify the statement.
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.
Draw an í- `delta` graph for a mono chromatic raY through a glass prism of a plane and mark
(i) `delta` m, the angle of mínimum devíation
(íí) Any two values of i for which value of `delta` ís same.
Rewrite the following statement by selecting the correct option:
If a ray of light strikes a glass slab at an angle of 600 with the surface of the slab, the angle of incidence must be __________________.
What is meant by the refraction of light?
Why upper surface of water contained in a beaker and above eye level appears silvery?
Which colour of light travels fastest in any medium except air?
Explain briefly what causes the twinkling of stars at night.
Name two instruments of the total refracting prism in which is used.
In what condition a prism is said to be in the position of minimum deviation? What is the direction of the refracted ray inside the prism in this condition?
A ray of light moves from a rare medium to a dense medium as shown in the diagram below. Write down the number of the ray which represents the partially reflected ray.
In the diagram below, PQ is a ray of light incident on a rectangular glass block.
How are the angles ‘i’ and ‘e’ related to each other?
The diagram shows the path of a ray of light through a rectangular glass block placed in a liquid of uniform density.
What is the angular, deviation of the emergent ray from the glass block with respect to the incident ray?
Trace a ray of light incident at 30° on a surface if travelling from glass to air. What is the angle of refraction in this case? (R.I. for glass = 3/2).
The speed of light in air is 3 × 108 ms-1. Calculate the speed of light in water. The refractive index of water is 4/3.
The diagram below shows two parallel rays A (Orange) & B (Blue) incident from air, on air-glass boundary.
- Copy and complete the path of the rays A and B.
- How do the speeds of these rays differ in glass?
- Are the two refracted rays in glass parallel? Give a reason.
