31/5/3 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) If the potential difference across the two ends of a conductor is 5 V and the current through it is 0·2 A, then what is the resistance of the conductor ?
Ans: R= v/I
=5/0.2
=2.5 Ω
2) Write the major hazard of nuclear power generation.
Ans:
- Storage and disposal of spent or used fuel.
SECTION B
3) Draw a labelled ray diagram to show the path of the reflected ray corresponding to the ray which is incident obliquely to the principal axis, towards the pole of a convex mirror. Mark the angle of incidence and angle of reflection on it
Ans:
4) What is the principle of an electric motor ? State the rule which is applied to determine the direction of force experienced by a current carrying conductor when kept in a magnetic field.
Ans: Principle :
When current carrying coil is placed in a magnetic field ,it experiences force as per Fleming’s left hand rule.
Fleming’s left hand rule:
According to Fleming’s left hand rule, stretch the thumb, forefinger and middle finger so that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point the direction of force acting on the conductor.
5) Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.
Ans:
- Formic acid / Methanoic acid HCOOH
- Putting a solution of weak /mild base like baking soda.
OR
A student prepared solutions of (i) an acid and (ii) a base in two separate beakers but forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will he distinguish between the two using
(a) phenolphthalein
- Acid + Phenolphthalein—–à Colourless
Base+ Phenolphthalein—-à Pink colour
and
(b) methyl orange ?
- Acid + Methyl Orange –à Red
- Base + Methyl Orange —à Yellow
SECTION C
6) What is a food chain ? Why is the flow of energy in an ecosystem unidirectional ? Explain briefly.
Ans: The series of living organisms taking part at various biotic level forms a food chain.
(i) An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers
(ii) The energy that is captured by the autotrophs does not revert back to the solar input.
(iii) The energy which is passed to the herbivores does not come back to the autotrophs.
(iv) As it moves progressively through the various trophic levels it is no longer available to the previous level
OR
(a) Why should National Parks be allowed to remain in their pristine form ?
Ans: Since interference will create disturbances in the protected area (National Park) / To maintain the selfsustainability in the protected area
(b) Why is reuse of materials better than recycling ?
Ans: Reuse of materials is better than recycling because the process of recycling use some energy, in the reuse strategy things are used of again and again
7) What is a dam ? List two main advantages and two ill effects of constructing a big dam.
Ans: Dam is a barrier built across a river or a stream for storage of water. Advantage:
i.) Storage of adequate water for irrigation.
ii.) Generation of electricity
Ill effects :
i.) Social problems
ii.) Economic problems
iii.) Environmental problems
8) (a) Write two water conducting tissues present in plants. How does water enter continuously into the root xylem ?
Ans:
- Xylem vessels and Xylem tracheids
- At the roots, cells in contact with the soil actively take up ions.
- Creates a difference in concentration of ions
- So water moves up.
(b) Explain why plants have low energy needs as compared to animals.
Ans: Since plants do not move and have large proportion of dead cells in many tissues. Thus plants have low energy needs.
9) ‘‘Nervous and hormonal systems together perform the function of control and coordination in human beings.’’ Justify the statement.
Ans: Control and coordination of functioning of various systems is under the direct Control of nervous system. It is the nervous system which governs the way, a particular organ has to work .This control is achieved by complex network of neurons which carry signals in the form of electric impulse, to and from the brain. The hormonal system on the other hand co-ordinates the functioning of nervous system. The hormonal system has indirect control on various functions. It tells a system to either slow down or pace according to the situation. Nervous and hormonal systems are complimentary to each other thus we can say that nervous and hormonal system perform their function of control and coordination together .
10) Define genetics. Why is decrease in the number of surviving tigers a cause of concern from the point of view of genetics ? Explain briefly.
Ans:
- The branch of biology which deals with the study of heredity and variation.
- The decrease in the number of surviving tigers is a cause of concern because fewer number of tigers impose extensive inbreeding among themselves, this limits the appearance of variation and put the species at a disadvantage if there are changes in the environment. Since the tigers fail to cope with the environmental changes, they may become extinct.
11) 2 g of ferrous sulphate crystals are heated in a dry boiling tube.
(a) List any two observations.
Ans: a) Observations:
- Colour changes from green to white
- Formation of reddish brown Ferric oxide (Fe2O3)/evolution of SO2/SO3 gas.
(b) Name the type of chemical reaction taking place.
Ans: Decomposition reaction
(c) Write balanced chemical equation for the reaction and name the products formed.
Ans:
OR
You might have noted that when copper powder is heated in a china dish, the reddish brown surface of copper powder becomes coated with a black substance.
(a) Why has this black substance formed ?
Ans: When copper is heated in air, oxidation takes place
(b) What is this black substance ?
Ans: CuO/Copper oxide
(c) Write the chemical equation of the reaction that takes place. (d) How can the black coating on the surface be turned reddish brown ?
Ans: 2 Cu + O2à 2 CuO
12) In an industrial process used for the manufacture of sodium hydroxide, a gas ‘A’ is formed as a by-product. The gas ‘A’ reacts with lime water to give a compound ‘B’ which is used as a bleaching agent in the chemical industry. Identify ‘A’ and ‘B’. Also give the chemical equations of the reactions involved.
Ans:
- A —–Cl2(Chlorine gas)
- B——CaOCl2 (Calcium oxychloride )
- 2NaCl +2H2Oà2NaOH + Cl2 + H2
- Cl2 + Ca(OH)2 àCaOCl2 + H2O
13) An ore on treatment with dilute hydrochloric acid produces brisk effervescence. Name the type of ore with one example. What steps will be required to obtain metal from the enriched ore ? Also write the chemical equations for the reactions involved in the process.
Ans:
- Carbonate ore
Zinc Carbonate
- Calcination
- Reduction:
ZnO + Cà Zn + CO
14) A concave mirror has a focal length of 20 cm. At what distance from the mirror should a 4 cm tall object be placed so that it forms an image at a distance of 30 cm from the mirror ? Also calculate the size of the image formed.
Ans: 1/v+1/u=1/f
1/v=1/f-1/u
1/u=1/-20+1/30
u=-60cm(without unit(cm) deduct 1/2 mark)
m=-v/u
m=-[-30/-60]
m=-1/2
h2/h1=m
h2=h1xm
h2=4x[-1/2]
h2=-2cm
OR
A real image 2/3rd of the size of an object is formed by a convex lens when the object is at a distance of 12 cm from it. Find the focal length of the lens
m=v/u
m=-2/3
-2/3=v/-12
v=8cm
1/f=1/v-1/u
1/r=1/v-1/u
1/f=1/8-1/-12
1/f=1/8+1/12
f=24/5
f=4.8
15) Magnetic field lines are shown in the given diagram. A student makes a statement that the magnetic field at ‘A’ is stronger than at ‘B’. Justify this statement. Also redraw the diagram and mark the direction of magnetic field lines.
Ans:
- Closeness (crowding) of magnetic field lines is directly related to the strength of the magnetic field.
- Strength of magnetic field at point ‘A’ (Pole) is more than at point ‘B’.
- If the student redraws the diagram and mark the arrows correctly (N to S).
SECTION D
16) (a) Distinguish between cross-pollination and self-pollination. Mention the site and product of fertilization in a flower.
Ans:
Cross Pollination |
Self Pollination |
Pollen is transferred from anther/stamen of one flower to the stigma of another flower. | Transfer of pollen from anther/stamen to the stigma of the same flower. |
- Site of fertilization – Ovary
- Product of
(b) Draw labelled diagram of a pistil showing the following parts : Stigma, Style, Ovary, Female germ cell
Ans:
OR
(a) Draw a diagram of human female reproductive system and label the parts :
Ans:
(i) which produce an egg.
-> Ovary
(ii) where fertilization takes place.
-> Oviduct or fallopian tube
(b) List two bacterial diseases which are transmitted sexually.
-> )Syphillis and Gonnorhoea
(c) What are contraceptive devices ? Give two reasons for adopting contraceptive devices in humans.
-> Chemicals or materials required to avoid pregnancy
(i) Controlling human population
(ii) To maintain good reproductive health any two
(iii) Maintain gaps between successive birth
17) (a) How is equal genetic contribution of male and female parents ensured in the progeny ? Explain.
Ans: When the gametes from male and female parent combine during sexual reproduction to form zygote, they contribute equal amount of DNA(half each). The normal body cells of human contain 46 chromosomes each. Human sperm cells and egg cells both have 23 chromosomes .So the combination of these 23 chromosomes from male and female each during sexual reproduction ensures equal genetic contribution to progeny (23+23 = 46).
(b) Does the occurrence of diversity of animals on Earth suggest their diverse ancestry also ? Discuss this point in the light of evolution.
Ans:
- Animals have a vast diversity in structures, they probably do not have a common ancestry because common ancestry may greatly limit the extent of diversity.
- Many of these diverse animals are inhabiting the same habitat , the evolution by geographical isolation and speciation is not likely to happen.
18) (a) A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find the position, nature and size of the image formed.
Ans: a) (i) 1/v-1/u=1/f
1/v=1/f+1/u
1/v=1/20+1/-30
1/v=1/60
v=60cm
(ii) Real, inverted and magnified
(iii) m=v/u
m=60/-30
m=-2
h’=m x h
h’=-2 x5
h’=-10cm
(b) Draw a labelled ray diagram showing object distance, image distance and focal length in the above case.
Ans:
19) Compare the power used in 2W resistor in each of the following circuits :
Ans: A)
- R = R1 + R2
R = 1Ω + 2Ω
R = 3Ω
- V=IR
I=V/R
I=6V/3Ω
=2 Ampere or 2A
- p=12R
=2x2x2
=8W
- b) p=v2/R
p=4×4/2
p=8w
or
A bulb is rated 40 W; 220 V. Find the current drawn by it, when it is connected to a 220 V supply. Also find its resistance. If the given bulb is replaced by a bulb of rating 25 W; 220 V, will there be any change in the value of current and resistance ? Justify your answer and determine the change.
Ans:
(i) p=40w
v=220 v
p=vi
I=p/v=40w/220v
=0.18A
(ii)R=v2/R
=220×220/40
=1210Ω
(iii) P=25W
V=220v
P=VI
I=P/V
=5/220=0.113 A
(IV) R=V2R
=220 x220/25
=1936 Ω
V) Yes there is a change in current and resistance
20) Answer the following questions based on the elements with atomic number 3 to 9 :
(a) Name the element with smallest atomic radius.
Ans: Element with smallest atomic radius –Fluorine /F
(b) Name the element which shows maximum valency.
Ans: Element with maximum valency— Carbon /C
(c) Name the element which is a metalloid.
Ans: Element which is metalloid —- Boron /B
(d) Name the element which is most electropositive.
Ans: Element which is most electropositive — Lithium /Li
(e) Write the chemical formula of the compound formed when the elements of atomic number 6 and 8 react together.
Ans: CO and CO2
21) (a) State the reason why carbon can neither form C4+ cations nor C4– anions, but forms covalent bonds. Also state reasons to explain why covalent compounds
Ans:
- Carbon cannot form C4+ ions as very high energy is required to remove 4 electrons
- Carbon cannot gain 4 electrons to form C4- ions as 6 protons cannot hold 10 electrons
(i) are bad conductors of electricity.
Ans: Co-valent compounds are bad conductor of electricity as they do not have free electrons.
(ii) have low melting and boiling points. (b) Write the structural formula of benzene, C6H6 .
Ans: Due to weak forces of attraction between the molecules, thus less energy is required for breaking the bonds.
b) Write the structural formula of benzene, C6H6 .
Ans:
or
(a) Define the term ‘isomer’.
Ans: Isomers are those compounds which have the same molecular formula but different structural formula.
(b) Two compounds have same molecular formula C3H6O. Write the name of these compounds and their structural formula.
Ans:
Propanal – CH3CH2CHO
Propanone – CH3COCH3
(c) How would you bring the following conversions :
(i) Ethanol to ethene
(ii) Propanol to propanoic acid
Ans:
SECTION E
22) A teacher gives a convex lens and a concave mirror of focal length of 20 cm each to his student and asks him to find their focal lengths by obtaining the image of a distant object. The student uses a distant tree as the object and obtains its sharp image, one by one, on a screen. The distances d1 and d2 between the lens/mirror and the screen in the two cases and the nature of their respective sharp images are likely to be
(a) (20 cm, 40 cm) and (erect and erect)
(b) (20 cm, 40 cm) and (inverted and inverted)
(c) (20 cm, 20 cm) and (inverted and inverted)
(d) (20 cm, 40 cm) and (erect and inverted)
Ans: c) (20 cm, 20 cm) and (inverted and inverted)
Give reason for your answer.
Reason: Only real and inverted image can be obtained on the screen and in both cases the image is formed at the principal focus.
23) The rest position of the needles in a milliammeter and voltmeter, not in use, are as shown in Figure A. When a student uses these instruments in his experiment, the readings of the needles are in the positions shown in Figure B. Determine the correct values of current and voltage the student should use in his calculations.
Ans: 38mA, 3.2 V
OR
(i) What does the graph depict about the dependence of current on the potential difference ?
-> V∝I
(ii) Find the current that flows through the resistor when the potential difference across it is 2·5 V.
Ans: at 2.5 V current will be 0.25 A
24) Draw labelled diagram to show the following parts in an embryo of a pea seed :
Cotyledon, Plumule, Radical
Ans:
OR
A student observed a permanent slide showing asexual reproduction in Hydra. Draw labelled diagram in proper sequence of the observations that must have been made by the student. Name the process of reproduction also.
Ans:
25) In the experiment ‘‘To prepare a temporary mount of a leaf peel to show stomata’’, glycerine and safranin are used. When and why are these two liquids used ? Explain.
Ans:
- Safranin is used to stain/colour the material for better view.
Glycerine prevents the leaf peel from getting it dried.
26) What would you observe on adding zinc granules to freshly prepared ferrous sulphate solution ? Give reason for your answer.
Ans: The solution turns
i.) green to colourless and
ii.) black coating is formed on Zinc .
Reason : Zinc is more reactive than iron so it displaces the iron from its salt solution.
27) How is the presence of an acid tested with a strip of red litmus paper ?
Ans:
- No change / As acid turns blue litmus to red , so there is a need of blue litmus paper . To get the blue litmus dip the red litmus paper into a basic solution and get blue colour .
OR
A student is performing an experiment to study the properties of acetic acid. Answer the following questions :
(i) Name the substance he must add to acetic acid to produce carbon dioxide.
-> Sodium hydrogen carbonate (NaHCO3) or Sodium Carbonate (Na2CO3)
(ii) Give the relevant chemical equation for the reaction.
Ans: 2CH3COOH + Na2CO3 -> 2 CH3COONa + H2O + CO2
or
CH3COOH +NaHCO3 CH3COONa + H2O + CO2
(iii) How would he test CO2 gas in the laboratory ?
Ans: Liberated CO2 is passed through lime water, which is turned to milky.
CBSE Class 10 Previous Question Paper 2019 Solution
- Science (Set No 31/1/1)
- Science (Set No 31/1/2)
- Science (Set No 31/1/3)
- Science (Set No 31/2/1)
- Science (Set No 31/2/2)
- Science (Set No 31/2/3)
- Science (Set No 31/3/1)
- Science (Set No 31/3/2)
- Science (Set No 31/3/3)
- Science (Set No 31/4/1)
- Science (Set No 31/4/2)
- Science (Set No 31/4/3)
- Science (Set No 31/5/1)
- Science (Set No 31/5/2)
- Science (Set No 31/5/3)