(c) An
element
X
forms
a
chloride
with
the
formula XCl2, which
is
a
solid
with
a
high
melting
point.
X
would
most
likely
be
in
the
same
group
of
the
Periodic
Table
as
(i) Na ii) Mg (iii) Al (iv) Si
Answer: (ii) Mg
d) The enzyme contained
by our saliva is called
(i) amylase (ii) lipase (ii) trypsin (iv) pepsin
Answer: (i) amylase
e) The part
of the brain that controls the posture and equilibrium of our body is
(i) diencephalon (ii) cerebrum (iii) cerebellum
(iv) medulla oblongata
Answer: (iii) cerebelum
(f) During the course
of evolution, the
process
: by which
the
characteristic
features
of the
members
of a species
modify
due
to the
influence
of various
factors
and
thus
give
rise
to the
organisms
with
new
characteristic
features is called
(i) speciation (ii) evolution (iii) inheritance (iv) variation
Answer: (i) speciation
(g) Where
should
an object
be placed
in front
of a convex lens to get
a real
image
of
the size of the object?
(i) At the principal
focus of the lens
(ii) At twice the focal length
(iii) At infinity
(iv) Between the optical centre and principal focus of the
Answer: (ii) At twice the focal length
(h) The least distance of distinct vision for a young adult with normal vision is about
(i) 25 m (ii) 25 cm (ii) 2.5 cm (iv) 2.5 m
Answer: (ii) 25 cm
(i) The practical unit of electrical energy 1 kWh means
(i)36x106 J
(ii) 3.6x106 J
(iii) 3.6x105 J (iv) 36x104 J
Answer: (ii) 3.6x106 J
(j) Which of the following is not an example of a bio-mass energy source?
(i) Wood (ii) Nuclear
energy (iii) Gobar gas (iv) Coal
Answer: (ii) Nuclear energy
Section-B
2. Give an example of a double displacement reaction.
Answer: An example of a double displacement reaction is
Na2SO4 (
aq) + BaCl2(aq) → BaSO4(s) +2NaCl(aq)
3. What is ductility of a metal? 1
Answer: Ductility is the capacity of a material to deform permanently in response to stress.
4. Which of the following hydrocarbons undergo addition reaction ? 1
C2H6, C3H8, C3H6, C2H2, CH4
Answer: C3H6, C2H2 will undergo addition reaction.
5. What is a dominant character? 1
Answer: Sexually reproductive organisms have two copies of the gene with the same characteristics. If the copies are not exactly the same then the character of the copy that appears is called the dominant character.
6. What is meant by power of accommodation of the eye? 1
Answer: The ability of the eye lens to change its focal length is called power of accommodation of the eye.
7. Take about 3 mL of sodium sulphate
solution in a test tube. In another test tube, take about 3 mL of barium chloride solution. Mix the two solutions and answer the following: 1+1=2
(a) Write the observation
of the above experiment.
(b) Write the chemical
equation of the above observation and mention the type of the reaction.
Answer: (a) Precipitation can be seen when the two liquids are mixed.
(b) The chemical equation of the observation shall be:
Na2SO4 (
aq) + BaCl2(aq) → BaSO4(s) +2NaCl(aq)
8. A metal compound 'A' reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle 1+1=2
(a) Name the gas that extinguishes
a burning candle.
(b) Write a balanced
chemical equation for the reaction if one of the compounds formed is calcium chloride.
Answer: (a) The gas that extinguishes a burning candle is CO2
(b) Balanced chemical equation for the reaction is-
CaCO3 (s)
+ 2HCl( l) → CaCl2(aq) + H2O (l) + CO2(g)
OR
What is neutralization reaction? Give two examples. 1+1=2
Answer: When acid and base reacts they neutralizes each other to produce salt and water. This reaction is called neutralization reaction.
Example of neutralization reaction are-
NaOH (Base) +
HCl (Acid)→ NaCl (Salt) + H2O (Water)
KOH (Base) +
HCl (Acid)→ KCl (Salt) + H2O (Water)
9. Name the respiratory
pigment present in our blood. State its function. 1+1=2
Answer: The respiratory pigment present in our blood is haemoglobin. Haemoglobin carries oxygen from the lungs and distributes it to different parts of the body .
10. Write two differences
between axon and dendrite. 2
Answer: (1) Axon transmits electrical impulses away from the cell body to other neurons, whereas dendrites transmit electrical impulses from outside to the cell body.
(2) A single neuron has only one axon, but has numerous dendrites.
11. What is the importance of DNA copying
in reproduction? 2
Answer: During reproduction, DNA copying ensures that each progenitor cell receives an equal number of DNA. DNA copy is not exactly the same as the offspring of DNA, resulting in diversity in the organism and contribute to evolution.
12. An object is placed at a distance
of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. 2
Answer: Given that, f= 15 cm
u= -10 cm
Since, 1/f=1/u + 1/v
1/v = 1/f-
1/u
= 1/15- 1/(-10)
= 2+3/30
= 1/6
v= 6
Therefor, image will be formed at a distance of 6 cm from the mirror. Image will be virtual and erect.
OR
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw its ray diagram. 2
Answer:
Here, u=25 cm, f=10 cm, h= 5 cm
13. A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric
charge that flows through the circuit. 2
Answer: Given, Current, I= 0.5 A
Time, t= 10 Minutes=
10*60= 300 Second
As, Q=It
= 0.5 ₓ 300
= 300 Coulomb
Therefore 300 coulomb electric charges flow through the circuit. OR
How much energy is given to each coulomb of charge passing through a 6 V battery? 2
Answer: We know that, Work done= Potential difference ₓ Electric charge
W = VQ
= 6 v ₓ 1 c
= 6 Joule
Therefore, 6 Joule energy should be given to each coulomb of charge.
14. Explain
in brief
how
ozone
layer
is getting
depleted. 2
Answer: Ozone is a tri-atomic molecule of oxygen. Although it is a toxic gas, it plays a very important role in the upper levels of the atmosphere. This ozone layer protects Earth's surface from harmful affects of sun's ultraviolet (UV) rays. However, due to the influence of certain substances produced by human activity ozone layer is depleting day by day . CFC ( Chloro fluoro carbon) is considered the most responsible for ozone layer depletion. It is produced by cooling devices such as AC, refrigerator etc. CFC decomposes ozone molecules and converts them into atmospheric oxygen molecules. This has led to a gradual decrease in the amount of ozone in the ozone layer, leading to its depletion.
15. Explain the
working function
of an electric
motor. 2
Answer: An electric motor is a rotating device that converts electrical energy into mechanical energy. It consists of a rectangular coil of copper wire, ABCD. The coil is placed between the two poles of the magnetic field in such a way that its AB and CD arms are perpendicular to the direction of the magnetic field. The
ends of the coil are connected to the two
halves P and Q of a split ring. The inner sides
of these halves are insulated and attached
to an axle. The external conducting edges of
P and Q touch two conducting stationary
brushes X and Y, respectively, as shown in
the figure below.
When electricity is passed through the coil ABCD, current flows in opposite directions in the two arms AB and CD. According to Fleming's left hand rule, the force acting on AB and CD will also be in opposite direction. This will cause the coil to rotate counterclockwise. After half turn, Q will touch X bracket and P will touch Y bracket. As a result, the direction of current in the coil will be reversed and flows in the direction of DCBA and as a result the force acting on the AB and CD will also be reversed and the coil will rotate half-way again. This process will continue and the coil will continue rotating in the same direction.
16. Give any two ways in which non-biodegradable substances would affect the environment. 2
Answer: Substances that do not decompose to a simpler form by biological processes are called non biodegradable substances. Non biodegradable substances can have some adverse effects on the environment. E.g.
1. These substances can remain in the environment for many days or years and it harms the ecosystem.
2. Non biodegradable substances such as plastics emit some toxic gases when exposed to water, wind and sunlight for a long period of time. These gases can cause various diseases such as cancer by causing ultimate damage to the metabolism of the organism. In addition, these gases can pollute air, soil and groundwater.
17. You have been provided with three test tubes. One of them contains distilled water and the other two contain an
acidic solution and a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube? 3
Answer: When the red litmus paper was dipped one after another in the solutions in the three test tubes, the liquid that will make the red litmus paper blue will be alkaline. This blue litmus paper can now be used for acid testing. If this blue litmus paper is dipped one after another in the remaining two samples, the liquid which will change its color to red will be acid and the liquid which can not change the color of the blue litmus paper will be distilled water.
OR
Which gas is usually
liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas? 1+1+1=3
Answer: Hydrogen gas is emitted when acid reacts with metals. For example, when sodium metal reacts with hydrochloric acid, sodium chloride salt and hydrogen gas is produced.
Na(s) + HCl(aq)→
NaCl(aq) + H2(g)
Test: If the gas produced from the reaction between metal and acid is passed through a soap solution, bubbles will form in the solution. When a burning candle is placed in the path of these bubbles, Hydrogen gas will burn with pop sound.
18. (a) Explain
the following in terms of gain or loss of oxygen with one example each
(i) Oxidation
(ii) Reduction
(b) Why should a magnesium
ribbon be cleaned before burning in air? 1+1+1=3
Answer: (a) (i) Oxidation: In a reaction, if a substance gains oxygen then it is said to be oxidized.
ZnO + C → Zn + CO, in the reaction C has got oxygen, so it is oxidized
(ii) Reduction: In a reaction, if a substance loses oxygen, the substance is said to be reduced. For example, in the above mentioned reaction, Zn loses oxygen, hence reduced.
(b) A magnesium ribbon has to be cleaned before burning in the air as magnesium reacts with atmospheric oxygen to form a layer of magnesium oxide (MgO). It needs to be cleaned to prevent subsequent reactions with oxygen.
19. (a) Which element
has twice as many electrons in its second shell as in its first shell?
(b) An atom has electronic
configuration 2, 8, 7. What is the atomic number of this element.
(c) Lithium, sodium, potassium
are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements? 1+1+1=3
Answer: (a) Carbon has twice as many electrons in its second shell as in its first shell
(b) Atomic number of the element having electronic configuration 2,8,7 is 17.
(c) All of these have 1 electron in the outermost shell of their atom.
OR
The position of three elements A, B and C in the Periodic Table are shown below :
Group16 Group 17
---- ---
---- A
---- ----
B C
(a) State whether
A is a metal or non-metal. 1
b) State whether
C is more reactive or less reactive than A. 1
(c) Will C be larger or smaller in size than B? 1
Answer: (a) A is non-metal.
(b) C is less reactive than A
(c) C is smaller in size than B
20. What is hormone? Give an example of a growth-promoting plant hormone. How does movement of the leaves of a sensitive plant differ from the movement of a shoot towards light? 1+1+1=3
Answer: Hormones are chemical messengers that are secreted into the blood stream directly by some specialist cells (endocrine gland). Hormones are very essential for the control and coordination of the body.
An example of growth promoting hormone in plants is Auxin.
The movement of the leaves of the sensitive plant is a movement caused by touch stimuli, it does not depend on the direction of the stimulus. Such movement is very fast and instantaneous. On the other hand, the movement of the stem towards light is due to the stimulus of light, which depends on the direction of stimulus i.e. the direction of light. This movement is very slow and takes place over a certain period of time.
OR
What is hydrotropism? How would you demonstrate
hydrotropism with the help of an experiment? 1+2=3
Answer: The movement of roots of a plant in the direction of water is called hydrotropism.
A seedling of a plant is planted in a pot with a little soil. Water is kept in a perforated pot at a distance from the seedling. This arrangement is kept like this for a few days. After few days the root of the plant will bend towards the water container as shown in the figure.
21. Describe the process of sexual reproduction in flowering plants. 3
Answer: Plants can reproduce by both sexual and asexual processes. Flowering plants usually reproduce through sexual reproduction. The flower of the plant is its reproductive organ. The stamens in the flower is the male and the pistil is female reproductive organs where the gametes are located. The stamens are the male reproductive organs where the pollen is produced. The female reproductive organ has three main parts-
Ovary, Style and Stigma. The ovary contains the ovules and each of them contains a single egg. The egg inside the ovary is called the female germ cell / Female gamete. Male gamete are formed inside the pollen grains. Male gametes are transferred to the stigma of the flower where they unite together. This process is called Fertilization. The cell formed by the union of two germ cells is called a zygote, from which new plants are born.
OR
How does reproduction help in maintaining stability to the populations of a species? 3
Answer: Reproduction is the only way for an organism to increase its population. Therefore, it is especially helpful in maintaining the stability to the population of an organism. The process of reproduction helps the organism to survive on the planet and prevents the organism from becoming extinct on the planet. In this way the organism maintains a balance between the ratio of birth to death. Reproductive processes lead to diversity and evolution in the organism.
22. Explain the relation between evolution and classification. 3
Answer: All living things have some common characteristics. One of the most common characteristics of all living things is that their body is made up of cells. According to Darwin's theory of evolution, living beings evolved from simple to complex structures. At the same time, their characteristics change. Since the classification of organisms is based on the characteristics they have, classification is closely linked with evolution. When two species of organisms have a common resemblance to each other, they become closely related to each other. Character traits differ between the first and second generation of organisms, which are descended from the same ancestor. From this it can be said that the evolution of species is reflected in their classification.
OR
How many pairs of sex chromosomes are contained by the human beings? Explain how is sex determined in a human child. 3
Answer: Human carry only one pair of sex chromosome.
In the case of human beings, 22 pairs of chromosomes are carried by the child which come from the father and mother. In addition, there is one pair of sex chromosome in human. In the case of females, this sex-determining chromosome stay in pair of and called the X chromosome. However, in the case of males, the sex-determining chromosomes do not matched properly. Therefore, in the case of females, the sex chromosome is XX and in males it is XY.
For both boys and girl's one X chromosome is always from the mother's side. Therefore, the sex of the child is determined on the basis of the flow of the sex chromosome from the father's side. If in the case of infants, one X chromosome flows from the father's side and the one X chromosome flows from the mother's side then the child will be a girl.. If one X chromosome flows from the mother's side and Y chromosome flows flow from the father's side then the child will be a boy.
23. Draw the ray diagram
to show how hypermetropia is corrected. The near point of a hypermetropic
eye is 1 m. What is the power of the lens required to correct this defect? (Assume that the near point of the normal eye is 0.25 m) 1+2=3
Answer:
Hypermetropic eye
Correction of hypermetropia
Second part: The near point for the normal eye is 0.25 m = 25 cm
Thus the object distance , u = -25 cm
Again, since the near point for the hyper metropic eye is 1 m,
Thus the image distance, v = -1 m = -100 cm
Using the lens formula,
1 / v-1 / u = 1 / f
-1 / 100- 1 / -25 = 1 / f
1 / f = 1 / 25- 1/100
1 / f = (4-1) / 100
f = 100/3 = 33.3 cm = 0.33m
Thus, power, P = 1 / f
P = 1 / 0.33 = +3.0 D
The power of the lens required for the correction of this disorder is +3D
OR
Why does the sun appear reddish
early in the morning? Draw the ray diagram of an arrangement for observing scattering
of light in colloidal solution. 1+2=3
Answer:During sunrise, when the sun is near the horizon, the sun's light travels a considerable distance through the relatively thick layers of the atmosphere before it enters our eyes. Therefore, the short-wavelength light in the sunlight is scattered by the particles in the atmosphere and sent away. Therefore, only the longest wavelength of light i.e. red comes to our eyes and sun appears reddish early morning.
Second part: A powerful light source (S) is placed in the focus of a converging lens. The lens will give a ray of parallel light. The rays of this light are allowed to pass through a clear glass container (T) filled with clear water. This ray of light is allowed to pass through a hole (C) of a thick paper. With the help of a second converging lens (L2), the image of the hole is produced in the screen MN. Sodium thiosulphate is dissolved in the water in the glass container. With the help of this device we will be able to observe the scattering of light in the colloidal solution.
24. The resistance
of a metal wire of length 1 m is 26 Ω at 20 °C. If the diameter
of the wire is 0.03 cm, what will be the resistivity of the metal at that temperature? 3
Answer: Given, the resistance of the wire, R = 26 Ω
Diameter d = 0.03 cm = 3ₓ10-4 m,
r = r= 3ₓ10-4 m/2
Length of wire, l = 1 m
Therefore, the resistivity of the wire, ρ = RA /l
= 1.84ₓ10-6 Ωm
OR
100
J of heat is produced in each second in a 4Ω resistor. Find the potential difference across the resistor. 3
Answer: Given that,
Resistance, R= 4 Ω
Heat produced, H= 100 J
Time, T= 1 S
Heat produced in a conductor,
H= I2Rt
Therefore Current, I= √H/Rt
= √100/4*1
= 5 A
Therefore potential difference across the two ends of the resistance
V=IR
=5*4= 20V
25. 25. Explain how does a Solenoid behave like a magnet. When is the force experienced
by a current-carrying conductor placed in a magnetic field largest? 2+1=3
Answer: A solenoid is a coil which is wound in the form of a tightly packed helix. When an electric current is passed through the wire of an solenoid, a magnetic field is created around it. This magnetic field is the same as the magnetic field created on either side of the bar magnet. One end of the solenoid behaves like a magnetic north pole and the other end behaves like a south pole. The magnetic lines of force inside the solenoid are parallel lines, so the magnetic field is uniform at all points inside the solenoid.
When the direction of current flowing through the conductor is perpendicular to the direction of the magnetic field, the force experienced by the conductor is maximum.
26. What are the qualities
of an ideal source of energy? Give the names of two energy sources that you would consider
to be exhaustible. 2+1=3
Answer: The qualities of an ideal energy source are:
(1) It should produce more energy per unit volume or mass.
(2) It should be easily available
(3) It should be easy to store and transport.
(4) I have to be economical.
Coal and petroleum are the two sources of energy which are exhaustible.
27. (a) You are given a hammer,
a battery, a bulb, wires and a switch. How could you use them to distinguish
between samples of metals and non-metals? 2
(b) Pratyush
took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it. What will be the action of the gas on the following? 2
(i) Dry litmus paper
ii) Moist litmus paper
(c) State
two ways to prevent the rusting of iron. 1
Answer: (a) Metals are malleable. So if we beat it with a hammer, we can make a thin sheet out of it. But if we beat non-metals by hammer, it will break. Metals, can conduct electricity. So when the battery and the bulb is connected with the help of the wire current will pass through it and the bulb will glow. But non-metals cannot conduct electricity. This is how we can distinguish between metals and non-metals.
(b) When sulphur is heated Sulfur dioxide is produced.
(i) Sulfur dioxide does not react with dry litmus paper in any way.
(ii) Sulfur dioxide reacts with wet litmus paper to convert blue litmus paper to red, as sulfur dioxide produces sulfuric acid when it comes in contact with water.
(c) Colour painting, galvanization, etc. can be used to prevent rusting of iron.
OR
(a) Explain
the formation of sodium chloride (NaCl) by transfer of electrons. 2
(b) What
are the ions present in NaCl? 1
(c) What are amphoteric
oxides? Give two examples
of amphoteric oxides. 1+1=2
Answer: (a) NaCl is a compound formed between metals and non-metals. It is formed by the transfer of electrons from metal to non metal.
The outermost shell of the sodium atom contains one electron (2.8.1). If this electron is released , the second shell will be the outermost shell and it will gain a stable octet (2.8) and form a cation (Na +). Chlorine, on the other hand, has 7 electrons in its outermost shell. If it receives one electron it can attains a stable octet configuration. When there is a reaction between sodium and chlorine, chlorine take the electrons released by sodium and forms anion (Cl-). The process of electron exchange is shown in the figure.
Because sodium and chloride ions have opposite charges, they attract each other and form sodium chloride by being bound by a strong electrostatic force of attraction.
(b) The ions in NaCl are sodium ions (Na +) and chlorine ions (Cl-).
(c) Metals oxides which react with both acids and bases to produce salts and water are called amphoteric oxides. Two examples of amphoteric oxides are zinc oxide (ZnO) and aluminum oxide (Al2O3).
28. (a) A mixture of oxygen
and ethyne is burnt for welding. Explain
why
a mixture
of ethyne
and
air
is not
used. 2
(b) What is esterification reaction? Write the name and structure of the product when ethanoic acid reacts with ethanol in presence of an acid catalyst. 1+1=2
(c) Write the names of the following compounds. 1
(i) (ii)
Answer: (a) The amount of heat generated during the welding of iron is very important. When a mixture of ethyne and oxygen is burned, it burns completely and produces more heat than a mixture of ethyne and air. Therefore, a mixture of oxygen and ethyne is burned during welding and mixture of ethyne and air is not used
(b) Ester is formed by the reaction between acid and alcohol. This is called an esterification reaction.
Ethyl acetate is a substance formed by the reaction of ethanol with ethanoic acid in the presence of an acid catalyst. Its structure is shown below-
(c) (i) Pentyne (ii) Propanal
OR
(a) What is homologous series? Explain with examples. 1+1=2
(b) Draw the structures of the following compounds : 1+1=2
(i) Hexanal (ii) Propanone
(c) Name two hydrocarbons which give addition reactions. 1
Answer: (a) Classes in which carbon compounds have the same functional group are called homologous
series. For example, the compounds having functional group -OH i.e. CH3OH, C2H5OH, C3H7OH, and
C4H9OH are homologous series and these are called alcohols.
(b) (i) (ii)
(c) Two hydrocarbons which give addition reaction are-ethyne, propene.
29. Draw a neat labelled
diagram of the longitudinal section of the human heart and show the direction of the flow of blood through the different chambers with arrow marks, and give a brief description of the blood
circulation through it. 2+3=5
Answer:
The human heart is a hand fist-like muscular organ that plays a key role in transporting blood throughout the human body. Because
both oxygen and carbon dioxide have to
be transported by the blood, the heart
has different chambers to prevent the
oxygen-rich blood from mixing with the
blood containing carbon dioxide.
The
carbon dioxide-rich blood has to reach
the lungs for the carbon dioxide to be
removed, and the oxygenated blood from
the lungs has to be brought back to the
heart. This oxygen-rich blood is then
pumped to the rest of the body.
We can follow this process step by
step. Oxygen-rich blood from
the lungs comes to the thin-walled upper
chamber of the heart on the left, the left atrium. The left atrium relaxes
when it is collecting this blood. It then contracts, while the next chamber,
the left ventricle, expands, so that the blood is transferred to it. When the
muscular left ventricle contracts in its turn, the blood is pumped out to
the body. De-oxygenated blood comes from the body to the upper
chamber on the right, the right atrium, as it expands. As the right atrium
contracts, the corresponding lower chamber, the right ventricle, dilates.
This transfers blood to the right ventricle, which in turn pumps it to the
lungs for oxygenation. Since ventricles have to pump blood into various
organs, they have thicker muscular walls than the atria do. Valves ensure
that blood does not flow backwards when the atria or ventricles contract.
OR
What is photosynthesis? What are the events that take place during this process? Write how does plant absorb carbon dioxide. 1+3+1=5
Answer: Carbon and energy requirements of the autotrophic organism are
fulfilled by photosynthesis. It is the process by which autotrophs take
in substances from the outside and convert them into stored forms of
energy. This material is taken in the form of carbon dioxide and water
which is converted into carbohydrates in the presence of sunlight and
chlorophyll.
The following events occur during this process -
(i) Absorption of light energy by
chlorophyll.
(ii) Conversion of light energy to chemical
energy and splitting of water molecules
into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to
carbohydrates.
Plants absorbs carbon dioxide through the stomata located in the leaves.
30. A 20 mm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. If the distance of the object from the lens is 15 cm, then 3+2=5
(a) find the nature, position
and size of the image
(b) find
the
magnification
of the
image.
Answer: Given that, focal length, f= 10 cmHeight of object, h= 20 mm= 2 cm
Object distance, u= -15 cm
height of image, h/= ?
Since, 1/v-1/u= 1/f
1/v= 1/u+1/f
= 1/(-15)+ 1/10
= 1/30
v= 30 cm
As v is positive hence the image is real and inverted and will form at a distance 30 cm on the other side of the lens.
(b) Magnification, m= h//h= v/u
Height of image,h/= h(v/u)
= 2(30/-15)= -4 cm
Therefore magnification, m = 30/-15= -2
OR
Find the power of a concave
lens of focal length 2 m. A concave lens has focal length of 15 cm. At what distance
should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification
and nature of the image produced
by the lens. 1+2+1+1=5
Answer: Given that, focal length , f = 2 m
Since, Power P=1/f
= ½ D = 0.5 D
Second part
Given, image distance, v = -10 cm
f = -15 cm
u = ?
As, 1/v-1/u= 1/f
1/u= 1/v - 1/f
= 1/(-10) – 1/(-15)
= 1/(-30)
u = -30 cm
Therefore, Object distance 30 cm
Magnification, m = u/v= -10/-30= 0.33 cm
31. Why should we conserve
forests and wildlife? State three main problems to construct large dams. 2+3=5.
Answer: Forests are areas of biodiversity. Every living being is essential for this biodiversity. The main goal of conservation of these biodiversity is to protect them from extinction because loss of biodiversity leads to imbalances in the ecosystem
The three major problems in the construction of large dams are-
(1) Social Problems: As a result of construction of big dams, farmers and tribal people are relocated. They are deprived of adequate compensation or rehabilitation.
(2) Economic Problems: Construction of large dams requires substantial funds. Most of these are public money. Lack of proper profits causes economic loss to the people.
(3) Environmental problems: Erosion of forest cover at the site of river embankments and loss of vast biodiversity.
OR
Why do we need to manage our resources? Write
your views regarding conservation of forests. 2+3=5
Answer: We are all aware of the problems arising out of the indiscriminate use of resources in our society. The concept of sustainable resource management emphasizes the need to conserve resources for future generations while meeting the current needs in the use of resources.
We need to manage our resources because these resources are limited. Moreover, due to increase in human population, demands for resources are also increasing day by day. Therefore, these natural resources need to be managed to meet the needs of the present and future generations of mankind without exhausting them unplanned in a short period of time.
Second part: Forests are the areas of biodiversity. Every living being is essential for this biodiversity. The main goal of conservation of these biodiversity is to protect them from extinction. Forest is the habitat for many wild animals and birds. Village people are greatly dependent on the forest for various essential resources such as leaves for grass, vegetables, for medicinal purposes, fruits for food, etc. Also, various industries in urban area are dependent on forest for raw materials. Forest conservation is essential for all round development and welfare of living world.
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