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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
State the conditions required for total internal reflection of light to take place
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Name two factors which affect the critical angle for a given pair of media. State how do the factors affect it.
Draw diagram to illustrate the total internal reflection.
Define critical angle for a given medium.
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Express the refractive index μ of a medium in terms of the angle of incidence i in air and the angle of refraction r in a denser medium.
State two advantages of using a right-angle prism as a reflector, rather than a plane mirror.
Images formed by totally reflecting prisms are brighter than the image formed by ordinary reflected light, why?
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What can you say about the value of the angle of deviation in such a situation?
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Complete the following diagram to show the path of the ray of a single colour in the diagram as if enters in and emerges out of the prism. Mark the angles wherever necessary. (Critical angle for glass = 42°).
A ray of light is incident as a normal ray on the surface of separation of two different mediums. What is the value of the angle of incidence in this case?
Solve Numerical example.
From the given data set, determine angular dispersion by the prism and dispersive power of its material for extreme colours. nR = 1.62 nV = 1.66, δR = 3.1°
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( aμg = refractive index of glass w.r.t, air aμw = refractive index of water w.r.t. air)
The entire light is reflected back into the denser medium is called ______.
Which of the following statements about total internal reflection is true?
Write any two uses of total internal reflection.
A green light is incident from the water to the air-water interface at the critical angle (θ). Select the correct statement.
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State two differences between normal reflection and total internal reflection.
