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Question
Explain briefly what causes the twinkling of stars at night.
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Solution
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.
RELATED QUESTIONS
A student traces the path of a ray of light passing through a rectangular glass slab and marks the angle of incidence i, angle of refraction r and angle of emergence e, as shown.
The correctly marked angle(s) is/are
(A) ∠ i only
(B) ∠ e only
(C) ∠ r only
(D) ∠ i and ∠ e
A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence (∠i). He then measures the corresponding values of the angle of refraction (∠r) and the angle of emergence (∠e) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be
(A) ∠i > ∠r > ∠e
(B) ∠i = ∠e > ∠r
(C) ∠i < ∠r < ∠e
(D) ∠i = ∠e < ∠r
The diagram alongside shows the refraction of a ray of light from air to a liquid.
- Write the values of (i) angle of incidence, (ii) angle of refraction.
- Use Snell’s law to find the refractive index of liquid with respect to air.
A ray of light enters a glass slab ABDC as shown in figure and strikes at the centre O of the circular part AC of the slab. The critical angle of glass is 42°. Complete the path of the ray till it emerges out from the slab. Mark the angles in the diagram wherever necessary.
-
- the angle of refraction and
- the angle of deviation for the ray?
Choose the correct alternative and rewrite the following:
A glass slab is placed in the path of convergent light. The point of convergence of light
What is meant by the refraction of light?
Why does a fisherman aim at the tail of fish during spearfishing?
A fish swimming in a pond seems nearer than it really is. Explain.
Draw ray of light bending towards the normal while passing from air to glass. Label your diagrams.
