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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
When rays of light are incident on a glass slab then the incident ray and emergent ray are _________ each other.
- perpendicular
- parallel
- opposite
- concurrent
A student traces the path of a ray of light passing through a rectangular glass slab and marks the angle of incidence i, angle of refraction r and angle of emergence e, as shown.
The correctly marked angle(s) is/are
(A) ∠ i only
(B) ∠ e only
(C) ∠ r only
(D) ∠ i and ∠ e
Draw a ray diagram to show the refraction of light through a glass slab and mark angle of refraction and the lateral shift suffered by the ray of light while passing through the slab.
Observe the following figure and answer the questions given under it:
1) How many times does refraction take place in the above figure?
2) What happens to the ray of light when it passes from air to glass?
3) What happens to the ray of light when it passes from glass to air?
4) What are the rays AB and CD in the figure called?
5) Define refraction.
A ray of light passes from glass into air. The angle of refraction will be:
(a) equal to the angle of incidence
(b) greater than the angle of incidence
(c) smaller than the angle of incidence
(d) 45°
How must light travel out of a substance if it is not going to be refracted?
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.
The highest refractive index is of ______.
The diagram alongside shows the refraction of a ray of light from air to a liquid.
- Write the values of (i) angle of incidence, (ii) angle of refraction.
- Use Snell’s law to find the refractive index of liquid with respect to air.
In fig 4.18, name the ray which represents the correct path of light while emerging out through a glass block.
How is the angle of emergence related to the angle of incidence when prism is in the position of minimum deviation? Illustrate your answer with help of a labelled diagram using an equilateral prism?
A postage stamp kept below a rectangular glass block of refractive index 1.5 when viewed from vertically above it, appears to be raised by 7.0 mm. Calculate the thickness of the glass slab.
The critical angle for glass-air is 45° for the light of yellow colour. State whether it will be less than, equal to, or more than 45° for (i) ref light, (ii) blue light?
A student traces the path of a ray of white light through a rectangular glass slab and marks, the angles of incidence (∠i) , refraction (∠r) and emergence (∠e) as shown. Which angle or angles has he not marked correctly?
(A) ∠i only
(B) ∠i and ∠r
(C) ∠i and ∠e
(D) ∠r and ∠e
While tracing the path of a ray of light passing through a rectangular glass slab a student tabulated his observations as given below:
|
S.NO. |
∠i |
∠r |
∠e |
|
I |
60° |
40° |
61° |
|
II |
50° |
36° |
51° |
|
III |
40° |
28° |
39° |
|
IV |
30° |
20° |
31° |
The correct observations is:
(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?
The critical angle for glass-air interface is :
A total reflecting equilateral prism can be used to deviate a ray of light through:
Which colour of light travels fastest in any medium except air?
Does the depth of a tank of water appear to change or remain the same when viewed normally from above?
State the relation between the refractive index μ and the velocity of light (vm) in that medium.
Comment on the statement ‘The refractive index of glass is 3/2.’
Explain briefly what causes the twinkling of stars at night.
The refractive index of air with respect to glass is defined: as gµa = sin i/sin r
Write down a similar expression for aµg in terms of angle i and r.
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?
Complete the ray diagram showing its emergence into the air after passing through the prism.
How will you verify the laws of refraction or how the refractive index of glass is determined in the laboratory?
The diagram shows the path of a ray of light through a rectangular glass block placed in a liquid of uniform density.
Show with the help of a ray diagram the path of the ray when incident ray normally falls on the first surface of the glass block and passes through the block and the liquid.
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).
Draw a diagram of a prism and label:
(i) the base,
(ii) the refracting surfaces,
(iii) the refracting edge,
(iv) the refracting angle in it.
A ray of light PQ is incident normally on the hypotenuse of a right-angled prism ABC as shown in the diagram given below:
(i) Copy the diagram and complete the path of the ray PQ till it emerges from the prism.
(ii) What is the value of the angle of deviation of the ray?
(iii) Name an instrument where this action of the prism is used.
The velocity of light in diamond is 121000 kms-1. What is its refractive index?
