Science:2010:CBSE:[Delhi]:Set-III
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Q1
What changes in colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes?
Marks:1View AnswerAnswer:
The blue-coloured copper sulphate solution becomes a green-coloured solution due to the formation of iron sulphate while a reddish brown-coloured layer gets deposited on grey-coloured iron nails.
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Q2
Explain why a ray of light passing through the centre of curvature of a concave mirror gets reflected along the same path.
Marks:1View AnswerAnswer:
A ray of light passing through the centre of curvature of a concave mirror gets reflected along the same path as the incident ray fall on the mirror along the normal to the reflecting surface.
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Q3
A charged particle enters at right angles into a uniform magnetic field as shown. What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field?
Marks:1View AnswerAnswer:
The charge on the particle is positive.
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Q4
How is the increasing demand for energy adversely affecting our environment?
Marks:1View AnswerAnswer:
Increasing demand for energy due to increasing population is straining the natural resources, disturbing ecological balance and causing climatic changes and pollution.
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Q5
The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide?
Marks:1View AnswerAnswer:
From the relation, f = R/2,
So, f = 25 cm.
The type of spherical mirror is convex mirror. -
Q6
What is nature of the image formed by a concave mirror if the magnification produced by the mirror is + 4?
Marks:1View AnswerAnswer:
Since the magnification produced by the mirror is (+ve),so the nature of the image formed will be virtual, erect & magnified.
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Q7
On what basis is a chemical equation balanced?
Marks:1View AnswerAnswer:
A chemical equation is balanced on the basis of law of conservation of mass according to which mass can neither be created nor be destroyed.
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Q8
Name the hormone that helps in regulating level of sugar in our blood. Name the gland that secrets it.
Marks:1View AnswerAnswer:
Hormone: Insulin
Gland: Pancreas -
Q9
A person lives near a forest. Make a list of four items which he can get from the forest to meet his daily needs.
Marks:1View AnswerAnswer:
Fruits, animal meat, firewood, and timber.
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Q10
Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
Marks:2View AnswerAnswer:
A chemical change can be confirmed by any of the following observations:
· Change in temperature
· Evolution of gas
· Change in colour
· Formation of precipitates
· Change in energyFor example: Calcium oxide reacts vigorously with water to produce calcium hydroxide. During this process, a large amount of heat is evolved, which increases the temperature of the reaction mixture system. This confirms that a chemical reaction has taken place.
