science k exam k lia kuch imp btado class 10th most important
cbse
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Q. Explain why a ray of light passing through the centre of curvature of concave minor gets reflected along the same path.
Ans.
The light falling on the centre of curvature is reflected back along the same path because the incident ray falls on the mirror along the normal to the reflecting surface.
Q. What is the important function of presence of ozone in earth’s atmosphere?
Ans.
Ozone is the Earth’s natural process for all life forms. It shields our planet from the UV radiations, as these ultraviolet rays are harmful for all the living things. Therefore, any change in the size of this layer will automatically affect the life of people, plants and animals living on earth.
Q. Dark reaction of photosynthesis does not need light. Do plants undergo dark reaction at night? Explain.
Ans.
Dark reaction does not mean that it occurs in the absence of light i.e., at night. Infact, it is the reaction occurring simultaneously with light reaction. It a chemical process occurring independent of light. This reaction is completely based on enzymes.
Q. How are we able to see distant and nearby objects clearly? Which part of eye helps in changing curvature of lens? Why no image is formed at blind spot?
Ans.
We can see distant and near objects clearly because of the property of accommodation of eye. Accommodation is the name given to the ability of the lens of the eye to change its focal length and produce focused images of both distant and near objects on the retina.
Ciliary muscle helps in changing curvature of the lens. They are attached to the lens and contract or release to change the lens shape and curvature.
No image is formed at blind spot because there are no photo receptors, i.e., cones and rods to detect the light and send it to brain.
Q. (a) Which property of carbon leads to formation of large number of compounds? Define it.
(b) What is the functional group in the following molecules?
(i) CH3CH2CH2OH
(ii) CH3COOH
Ans.
(a) The two features of carbon that give rise to a large number of compounds are as follows:
(i) Catenation: It is the ability to form bonds with other atoms of carbon.
(ii) Tetravalency: With the valency of four, carbon is capable of bonding with four other atoms.
(b)
Compound
Functional group
(i) CH3CH2CH2OH
-OH (Hydroxyl group)
(ii) CH3COOH
-COOH (Carboxyl group)
Q. (a) Why magnification is taken negative for real images and positive for virtual images?
(b) Why convex mirror is used in rear view mirrors and not concave mirror?
Ans.
(a) If image is real, it will be inverted which means height of image will be taken as negative. Also, the height of object is always positive.
Now as magnification = Height of image / Height of object.
Therefore, in case of real image,
Magnification = Height of image (-) / height of object (+)=Negative.
So, Magnification will be negative.
Similarly, if image is virtual, it will be erect.
Therefore, in case of virtual image,
Magnification = Height of image (+) / height of object (+)= Positive
So, Magnification will be positive.
(b) Convex mirror is commonly used in rear view mirrors in vehicles because it gives an erect, virtual, full size diminished image of distant objects with a wider field of view. Thus, convex mirrors enable the driver to view much larger area which is not possible with a concave mirror.