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प्रश्न
Explain ‘mirage’ as an illustration of refraction.
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उत्तर
- On a hot, clear, sunny day, along a level road, there appears a pond of water ahead of the road. However, if we physically reach the spot, there is nothing but the dry road, and the water pond again appears some distance ahead. This illusion is called a mirage.
- Mirages result from the refraction of light through a non-uniform medium.
- On a hot day the air in contact with the road is hottest, and as we go up, it gets gradually cooler. The refractive index of air thus decreases with height. Hot air tends to be less optically dense than cooler air, which results in a non-uniform medium.
- Light travels in a straight line through a uniform medium but refracts when travelling through a non-uniform medium.
- Thus, the ray of light coming from the top of an object gets refracted while travelling downwards into less optically dense air and becomes more and more horizontal, as shown in the figure.
- As it almost touches the road, it bends (refracts) upward. Then onwards, upward bending continues due to denser air.
- As a result, for an observer, it appears to be coming from below, thereby giving an illusion of reflection from an (imaginary) water surface.
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संबंधित प्रश्न
Draw the diagram of a right-angled isosceles prism which is used to make an invented image erect.
State two conditions necessary for total internal reflection to occur.
Draw diagram to illustrate the total internal reflection.
Write the necessary conditions for the phenomenon of total internal reflection to
occur ?
Total internal reflection can take place only if ______.
Define critical angle for a given medium.
Plot a graph between
Angle of incidence versus angle of reflection,
If a light ray does not undergo, refraction at the boundary between two media, the angle of incidence is:
Make the correct choices for each of the following :
Total Internal reflection takes place when
(where ∠i = angle of incidence, ∠r = angle of refraction, ∠C = critical angle)
If a ray of light passes from medium I to medium II without any change of direction, what can be said about the refractive indices of these media (angle I is not 0)?
State one factor on which a critical angle for a given pair of media depends. The critical angle for the glass-air interface is 45° for the yellow light. Will it be equal to, less than or greater than 45° for (i) red light, (ii) blue light?
Name the factors affecting the critical angle for the pair of media.
Draw a diagram, properly labelled, to illustrate the use of a total reflecting prism (a right-angled isosceles prism) to turn a ray of light through 180°. Name an instrument in which this device is used.
The adjacent diagram shows two right-angled isosceles prisms A and B. Complete the diagram to show the path of rays P and Q emerging out of the prism B. What principles have you used to complete the diagram?
PQ and PR are two light rays emerging from the object as shown in the figure below:
(i) What is the special name given to the angle of incidence (∠PQN) of ray PQ?
(ii) Copy the ray diagram and complete it to show the position of the image of the object P when seen obliquely from above.
(iii) Name the phenomenon that occurs if the angle of incidence ∠PQN is increased still further.
Choose the correct option.
Select the WRONG statement.
Which of the following is not involved in formation of a rainbow?
Answer the following question.
What are the advantages of optical fibre communication over electronic communication?
Answer the following question.
Why is prism binoculars preferred over traditional binoculars? Describe its working in brief.
The resultant `vec"R"` of `vec"P"` and `vec"Q"` is perpendicular to `vec"P"`. Also `|vec"P"|=|vec"R"|`. The angle between `vec"P"` and `vec"Q"` is ______.
[tan 45° = 1]
For the same angle of incidence, the angle of refraction in four media A, B, C and D are 25°, 30°, 35° and 40° respectively. The speed of light is least in medium ______.
Which of the following statements about total internal reflection is true?
Optical Fibres are based on the phenomenon of dispersion.
What is a mirage? How does it occur?
A Rainbow is a beautiful natural phenomenon formed because of the following:
Observe the given figure of the raindrop and answer the following questions:
- Label A and B of the given diagram. Why colour will deviate most.
- Name the phenomenon shown in label C.
Which of the following is used in optical fibres?
- Assertion (A): Propagation of light through an optical fibre is due to total internal reflection taking place at the core-cladding interface.
- Reason (R): Refractive index of the material of the cladding of the optical fibre is greater than that of the core.
Small air bubbles rising up a fish tank appear silvery when viewed from some particular angle is due to the ______.
