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प्रश्न
Explain how spectrum is formed.
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उत्तर
When white light passes through a glass prism, it spreads out into a band of different colours called the spectrum of light.
- When white light is dispersed into seven colours by a glass prism, different colours bend through different angles with respect to the incident ray.
- The sequence of colours given by the prism is Violet, Indigo, Blue, Green, Yellow, Orange and Red.
- Of the seven colours, red light bends the least, while violet light bends the most. So, the rays of each colour emerge along different paths and appear distinct. Hence, we get a spectrum of seven different colours.
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संबंधित प्रश्न
What is a spectrum?
Write a short note on dispersion of light.
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
If the speed of light in vacuum is 3 × 108 ms−1, find the speed of light in a medium of absolute refractive index 1.5.
A ray of light passes from water to air. How does the speed of light change?
Why is the ratio of the velocities of light of wavelengths 4000Å and 8000Å in vacuum 1: 1?
How is the reflection of light ray from a plane mirror different from the refraction of light ray as it enters a block of glass?
When light travels from a rarer to a denser medium, its speed ______.
A ray of light of wavelength 6600 Å suffer refraction from air to glass. Taking \[\ce{_a\mu_g = \frac{3}{2}}\], find the wavelength of light in glass.
Name the colour of white light which is deviated the most on passing through a prism.
An object is viewed through a glass prism with its vertex pointing upwards. It appears to be displaced upward. Explain the reason.
Complete Fig. 4.32 to show the path of the ray of single colour as it enters the prism and emerges out of it. Mark the angles wherever necessary.
What is meant by the statement the critical angle for diamond is 24°?
The refractive index of air with respect to glass is expressed as `""_g μ_a=sin i /sin r`.
- Write down a similar expression for aμg in terms of the angles i and r.
- If angle r = 90°, what is the corresponding angle i called?
- What is the physical significance of the angle i in part (b)?
Rahim recorded the following sets of observations while tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence.
|
S. No. |
Angle of incidence |
Angle of refraction |
Angle of emergence |
|
I |
45° |
41° |
45° |
|
II |
40° |
38° |
38° |
|
III |
45° |
41° |
40° |
|
IV |
41° |
45° |
41° |
The correct observation is recorded at serial number:
(1) I
(2) II
(3) III
(4) IV
Define the term refractive index of a medium. What do you understand by the statement 'the refractive index of glass is 1.5 for white light'?
In the fig., PO is a ray of light incident on a rectangular glass block.
(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.
A ray of light strikes the surface at a rectangular glass slab such that the angle of incidence is 45o.
In each case, draw diagram to show the path taken by the ray as it passes through the glass slab and emerges from it.
Name the phenomenon responsible in the following case:
Apparent bending of a stick in water
Why is the colour red used as a sign of danger?
A fish swimming in a pond seems nearer than it really is. Explain.
What is the refractive index of vacuum
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.’
Define the term refractive index of a medium in terms of velocity of light.
How does the angle of deviation produced by a prism depend on the colour of light used? Which colour of white light is deviated (i) most, (ii) least, by a prism?
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?
Draw a diagram to show the refraction of a monochromatic light ray through an equilateral prism. On the diagram, label the incident, refracted, and emergent rays. It also indicates the angle of deviation by the letter δ.
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?
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?
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.
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?
Write the approximate values of speed of light in (i) air and (ii) glass. Use these values to calculate the refractive index of glass with respect to air.
Observe the figure and name the ray AB, ray CD, ray GH.
