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प्रश्न
Write a short note on dispersion of light.
उत्तर
Dispersion of light:-
The phenomenon of splitting of light into its component colours is called dispersion of light. When white light passes through a glass prism, it spreads out into a band of different colours which constitute the spectrum of light. The colours in the spectrum of white light are violet, indigo, blue, green, yellow, orange and red. Dispersion takes place because the refractive index of a material such as glass or water is different for different colours. It is maximum for violet colour and minimum for red colour. Hence, in the spectrum of white light obtained with a prism, violet light is deviated the most, while red light is deviated the least. The deviation of light corresponding to other colours lies in between these two colours.
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संबंधित प्रश्न
Explain how spectrum is formed.
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
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
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.
Four students P, Q, R and S traced the path of a ray of light passing through a glass slab for an angle of incidence 40° and measured the angle of refraction. The values as measured them were 18°; 22°; 25° and 30° respectively. The student who has performed the experiment methodically is
(A) P
(B) Q
(C) R
(D) S
On the basis of the experiment, "To trace the path of a ray of light through a rectangular glass slab", students of a class arrived at which one of the following conclusions?
(A) Angle of incidence is greater than the angle of emergence.
(B) Angle of emergence is smaller than the angle of refraction.
(C) Emergent ray is parallel to the refracted ray.
(D) Incident ray and emergent ray are parallel to each other.
Explain the term absolute refractive index of a medium and write an expression to relate it with the speed of light in vacuum.
Why is the ratio of the velocities of light of wavelengths 4000Å and 8000Å in vacuum 1: 1?
Which of the above wavelengths has a higher frequency?
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).
Draw diagrams to show the refraction of light from glass to air. In diagram, label the incident ray, refracted ray, the angle of incidence (i) and the angle of refraction (r).
How is the refractive index of a medium related to the speed of light in it?
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.
In the adjacent diagram, AO is a ray of light incident on a rectangular glass slab.
- Complete the path of the ray till it emerges out of the slab.
- 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?
- Mark angles of emergence by the letter e. How are the angles i and e related?
- Which two rays are parallel to each other? Name them.
- Indicate in the diagram the lateral displacement between the emergent ray and the incident ray. State one factor that affects the lateral displacement.
When a ray of light from air enters a denser medium, it ______.
What do you understand by the statement the refractive index of glass is 1.5 for white light?
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 Water pond appears to be 2.7 m deep. If the refractive index of water is 4/3, find the actual depth of the pond.
What is meant by the statement the critical angle for diamond is 24°?
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 falls normally on the surface of a transparent glass slab. Draw a ray diagram to show its path and also mark angle of incidence and angle of emergence.
-
- the angle of refraction and
- the angle of deviation for the ray?
Make the correct for each of the following :
With reference to the fig, the refractive index of the glass block is
Which colour of light travels fastest in any medium except air?
A total reflecting equilateral prism can be used to deviate a ray of light through:
A fish swimming in a pond seems nearer than it really is. Explain.
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?
The refractive index of air with respect to glass is defined: as gµa = sin i/sin r
If r = 90°, what is the corresponding angle i called?
The refractive index of glass with respect to air is 1.5. What is the value of the refractive index of air with respect to glass?
