What is the principle of reversibility of light? Show that the i

Subject

Science

Class

CBSE Class 10

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 Multiple Choice QuestionsShort Answer Type

21.

The atomic number of an element is 16.Predict

i) the number of valence electrons in its atom

ii)its valency

iii) its group number

iv) whether it is a metal or a non-metal

v) the nature of oxide formed by it

vi)the formula of its chloride

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22.

State any four characteristics of the image of an object formed by a plane mirror.

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23.

Draw a ray diagram to show the refraction of light through a glass prism. Mark on it
a) the incident ray, b) the emergent ray and c) the angle of deviation.

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24.

Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon?

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25.

An object is placed between infinity and the pole of a convex mirror. Draw a ray diagram and also state the position, the relative size and the nature of the image formed.

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26.

What is the principle of reversibility of light? Show that the incident ray of light is parallel to the emergent ray of light when light falls obliquely on a side of a rectangular glass slab.


The principle of reversibility of light states that the light ray after reflection or refraction, when reversed, will retrace its path.

Using the Snell's law,

When light ray falls from a rarer to denser medium, then

n21fraction numerator sin space straight i over denominator sin space straight r end fraction
When retraced, the ray will move from denser to rarer medium.

That is,

straight n subscript 12 space equals space fraction numerator sin space straight r over denominator sin space straight i end fraction
Therefore,
straight n subscript 21 space straight x space straight n subscript 12 space equals space open parentheses fraction numerator sin space straight i over denominator sin space straight r end fraction close parentheses space straight x space open parentheses fraction numerator sin space straight r over denominator sin space straight i end fraction close parentheses equals 1

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27.

What eye-defect is myopia? Describe with a neat diagram how this defect of vision can be corrected by using a suitable lens?

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28.

What is meant by biological magnification?

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29.

Give an example to illustrate that indiscriminate use of pesticides may result in the degradation of the environment.

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30.

List any, four reasons for vegetative propagation being practised in the growth of some type of plants. 

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