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CBSE Class 10 Science Solved Question Paper 2012

Short Answer Type

21.

State one role of ciliary muscles in the human eye?

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22. To construct ray diagram we use two light rays which are so chosen that it is easy to know their directions after reflection from the mirror. List these two rays and state the path of these rays after reflection. Use these rays to locate the image of an object placed between centre of curvature and focus of a concave mirror.

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23.

What is the colour of the sky during day time? Give reason for it?

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24.

Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.

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25. A 5 cm tall object is placed perpendicular to the principle axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 8 cm. Using the lens formula, find the position, size and nature of the image formed.

Given,

Object distance from the lens, u = - 8 cm

Focal length of the lens, f = 12 cm

Height of the object, h = 5 cm

Using the lens formula,

$1 over straight v minus 1 over u equals 1 over f$

Putting the values,

$1 over straight v equals 1 over 12 plus fraction numerator negative 1 over denominator 8 end fraction space space space space equals space 1 over 12 minus 1 over 8 space space space space equals space fraction numerator 2 minus 3 over denominator 24 end fraction space space space space equals space fraction numerator negative 1 over denominator 24 end fraction rightwards double arrow space v space equals space minus 24 space c m$

Thus, image is formed 24 cm on the left of the convex lens.

That is, object is formed on the same side of the object.

Now,
Magnification, m = $straight v over straight u equals fraction numerator h apostrophe over denominator h end fraction equals fraction numerator negative 24 over denominator negative 8 end fraction equals fraction numerator h apostrophe over denominator 5 end fraction$
That is,

Height of the image, h' = 15 cm (positive)

Height of the image is 15 cm which is 3 times larger than the height of the object.

Therefore, the image formed is virtual, enlarged and erect.

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26.

State the types of mirrors used for: i) headlights and ii) rear view mirror, in cars and motorcycles. Give to justify your answer in each case.

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27. An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the:

(i) defect of vision and also (ii) for its correction.

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