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प्रश्न
Explain briefly what causes the twinkling of stars at night.
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उत्तर
Stars are very far from us. The light ray coming from a star undergoes successive refractions on entering the earth’s atmosphere and bends towards the normal. Hence, an apparent image of the star is seen. Simultaneously due to the movement of air, the refractive index of layers of atmosphere keeps on changing, i.e., the apparent position of star keeps changing. Thus, the star appears to twinkle.
संबंधित प्रश्न
Choose the correct alternative and rewrite the following sentence.
A ray of light strikes the glass slab at an angle of 50°. What is the angle of incidence?
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.
A ray of light is passing from a transparent medium 1 to another transparent medium 2 (i) Speed up (ii) slows down. In each case, state whether the refractive index of medium 2 is equal to, less than or greater than the refractive index of medium 1.
Fill in the blanks to complete the following sentence
The refractive index of glass with respect to air is 3/2. The refractive index of air with respect to glass will be ……………….
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 interface is :
Why do the faces of persons sitting around campfire appear to shimmer?
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.
The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as A, B, C and D in the figure. Which one of them is correct?
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| A | B | C | D |
