31/4/3 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Mention the condition under which a current can flow in a conductor.
Ans: Potential difference between ends of conducter
2) List two merits of solar cells.
Ans: (i) Uses renewable sources of energy.
(ii) Maintenance cost is very less.
(iii) Long life.
SECTION B
3) List four characteristics of the image formed by a convex lens of focal length 20 cm when the object is placed in front of it at a distance of 10 cm from its optical centre.
Ans: (i)Erect (ii) virtual (iii) magnified (iv) same side of the object
OR
Define refractive index of a transparent medium. The speed of light in a medium of absolute refractive index 1·5 is 2 ´ 108 ms–1. What is the speed of light in vacuum ?
Ans:
Refractive index is the ratio of speed of light in air or vacuum to speed of light in medium. Mathematically: Refractive index of a medium 1.5
Speed of light in medium = 2×108 ms-1 Speed of light in vacuum?
µ = speed of light in vacuum / speed of light in medium
speed of light in vacuum = 1.5 x 2 x 108 ms-1
3 x 108 ms -1
4) It is established that an electric current through a conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles, (ii) neutrons ? Justify your answer in each case.
Ans:
- Yes because alpha particles are positively charged and moving charged particles produce magnetic field .
- No because neutron has no charge. No magnetic field produced.
5) ‘‘Conversion of ethanol to ethanoic acid is an oxidation reaction.’’ Justify this statement giving the relevant equation for the chemical reaction involved.
Ans:
Alk.KMnO4 is working as a oxidizing agent so it oxidizes Ethanol to ethanoic acid
SECTION C
6) List three roles of forests in conserving the environment. How do the forests get depleted ? State two consequences of deforestation on the environment.
Ans:
- Conserving the environment: Preventing pollution/bring rainfall/ oxygen supply (or any other )
- Depletion: Deforestation / increase in population / scarcity of water (or any other)
- Consequences: Reduction in rainfall / reduction in the yields of forest products / imbalance in eco system
7) (a) Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. Why ?
Ans:
Manmade ecosystem |
Natural ecosystem |
no microbes to clean the water |
microbes to clean the water |
(b) What are decomposers ? What will be the consequence if the decomposers are completely eradicated from an ecosystem ? Give justification in support of your answer.
Ans: The micro-organisms that breakdown the complex organic substances into simple inorganic substances.
- No decomposition would take place.
- Soil would be unsuitable for crops/it would result in imbalance in Ecosystem
- nutrients would not returned back to the nutrient pool
- Land pollution/affect soil fertility or any other
OR
How is ozone formed in the upper atmosphere ? State its importance. What is responsible for its depletion ? Write one harmful effect of ozone depletion
Ans:
- The higher energy UV radiations split apart some molecular oxygen into free oxygen atoms . These atoms then combine with molecular oxygen to form ozone..
- It prevents harmful UV radiation to reach the earth.
- CFC/chlorofluoro carbon/aerosol
Skin cancer/reduction in immune system/cataract/damages eyes
8) State right-hand thumb rule to determine the direction of magnetic field around a current carrying conductor. Apply this rule to find the direction of magnetic field inside and outside a circular loop of wire lying in the plane of a table and current is flowing through it clockwise.
Ans:
- Right hand thumb rule: If we hold a current carrying straight conductor in our right hand , such that the thumb gives the direction of electric current then the curled fingers give the direction of the magnetic field.
- The magnetic field will be directed perpendicular into the plane of table inside the circular loop.
- The magnetic field will be directed perpendicular outside plane of table for a point outside the circular loop. / Diagram:
9) What is the cause of dispersion of white light through a glass prism ? Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the faces of the prisms.
Ans:
- Cause of dispersion:
(i) Shape of prism
(ii) Different colours bend with different angles (different colour has different refractive index or different speed) diagram
Arrow& labelling
OR
What is scattering of light ? Use this phenomenon to explain why (i) the Sun appears reddish at sun-rise, and (ii) the clear sky appears blue
Ans: Scattering of light means to throw light in all possible direction when light intract with particles of medium.
(i)The Sun appears reddish at sun-rise : the Sun rays have to travel through a large atmospheric distance near the horizon .As the wave length of red light is maximum in the visible range , hence the scattering is least . The blue light and shorter wavelengths are scattered away by the particles .This gives rise to the reddish appearance of the sun./diagrammatic answers may be given fig:11.12
(ii)The sky appears blue: Blue colour has shorted wavelength than red. When sunlight passes through the atmosphere, the fine particles in the air scatter the blue light more strongly than red. Hence the clear sky spears blue.
10) A metal X, which is used in thermit process, when heated with oxygen gives an oxide Y which is amphoteric in nature. Identify X and Y. Write balanced chemical equations of the reactions of oxide Y with hydrochloric acid and sodium hydroxide.
Ans:
X=Al , Y = Al2O3
Al2O3 + 6HCl -> 2AlCl3 + 3H2O
Al2O3 + 2NaOH -> 2NaAlO2 + H2O
11) A white powder is used by doctors to support fractured bones.
(a) Write the name and chemical formula of the powder.
Ans: Plaster of Paris
CaSO4.½H2O(Calcium sulphate hemihydrate)
(b) How is this powder prepared ?
Ans: Heating calcium sulphate dihydrate, or gypsum, to3730 K.
(c) When this white powder is mixed with water, a hard solid mass is obtained. Write a balanced chemical equation for the change.
Ans: on addition of water it sets into hard mass.
CaSO4½H2O + 1½H2O -> CaSO4. 2 H2O
(d) Give one more use of this white powder.
Ans: Making sculptures/statues / Decorative items/POP walls
12) (a) Classify the following reactions into different types :
(i) AgNO3 (aq) + NaCl(aq) -> AgCl(s) + NaNO3 (aq)
Ans: i) double displacement reaction
ii) CaO(s) + H2O(l) -> Ca(OH)2 (aq)
Ans: combination reaction
Ans: decomposition reaction
iv) Zn + CuSO4 -> ZnSO4 + Cu
Ans: displacement reaction
b) Translate the following statement into a balanced chemical equation : ‘‘Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate.’’
Ans: 3BaCl2 + Al2(SO4)3 ->2AlCl3 + 3BaSO4
OR
When potassium iodide solution is added to a solution of lead (II) nitrate in a test tube, a precipitate is formed.
(a) What is the colour of this precipitate ? Name the compound precipitated.
Ans: Yellow, lead iodide
(b) Write the balanced chemical equation for this reaction.
Ans: 2KI +Pb(NO3)2 ->PbI2 + 2KNO3
(c) List two types of reactions in which this reaction can be placed.
Ans: Double displacement, precipitation reaction
13) Draw a diagram of human excretory system and label the following : (i) Urinary bladder (ii) Left kidney (iii) Left ureter
Ans:
14) (a) Plants do not have any nervous system but yet, if we touch a sensitive plant, some observable changes take place in its leaves. Explain how could this plant respond to the external stimuli and how it is communicated.
Ans: The plant will immediately change the shape by changing the amount of water in them (swelling or shrinking) thus bringing movement.
(b) Name the hormone that needs to be administered to
(i) increase the height of a dwarf plant.
Ans: Gibberellin/Auxin
(ii) cause rapid cell division in fruits and seeds.
Ans: Cytokinin
15) What are fossils ? Describe briefly two methods of determining the age of fossils.
Ans:
- Fossils are dead remains or traces of preserved plants and animals buried under the earth’s crust.
- Relative Dating:Digging the earth shows that the fossils closer to the earth surface are more recent than those in the deeper layers.
- Carbon Dating: Detecting the ratios of different isotopes of the same element in the fossil material
16) (a) Define vegetative propagation. List its two methods.
Ans: Reproduction through vegetative parts of a plant like Roots / stem / leaves/Artificial / Layering / Grafting
(b) Why is this mode practised for growing some types of plants ?
Ans: (i) In some plants which produce non viable seeds.
(ii) It consumes less time / fast method
(c) Explain the process of budding in Hydra with the help of labelled diagrams.
Ans: Budding in hydra:
OR
What is contraception ? List its four different methods. State four reasons for adopting contraceptive methods.
Ans:
- Prevention of unwanted pregnancy.
- Method :
(i) mechanical barrier – condom
(ii) surgical method – tubectomy / vasectomy
(iii) chemical – Oral and vaginal pills (iv) IUCD / copper –T
- Reasons:
(i) Gap between children
(ii) mother’s health
(iii) better living standard
(iv) population under control
17) (a) List in tabular form two differences between acquired traits and inherited traits.
(b) Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it.
Ans:
Acquired Traits |
Inherited Traits |
These traits are not transferred from one generation to the next generation | These traits are transferred from one generation to the next |
They do not bring about change in DNA | They bring about changes in DNA |
They do not direct evolution | They do direct evolution. |
- For limbs of human beings
- These characteristics show similarities since they have a common ancestor but are modified to perform the different functions.
Homologous characteristics helps to identify the relationship between organisms. These characters in different organisms could be similar because they have been inherited from a common ancestor.
18) (a) Distinguish between esterification and saponification reactions with the help of chemical equations for each.
Ans:
(b) With a labelled diagram describe in brief an activity to show the formation of an ester.
Ans: Diagram for esterification
Description
1mL ethanol, 1mL glacial acetic acid and a few drops of conc. H2SO4 -> Warmed in a water bath ->Water is poured into the beaker-> Fruity smell is produced
OR
What is the difference between soaps and detergents ? State in brief the cleansing action of soaps in removing an oily spot from a fabric. Why are soaps not very effective when a fabric is washed in hard water ? How is this problem resolved ?
Ans:
- Soaps are sodium salts of fatty acids.
- Detergents are sodium salts of sulphonic acids. Soaps do not act in hard water due to formation of scum while detergents do.
- Cleansing action of soaps: In soaps carbon chain dissolves in oil and the ionic end dissolves in water to form micelle
- Hard water contains Ca2+ / Mg2+ ions that react with soap and form precipitates called scum.
- By using detergents in hard water / boiling hard water
19) (a) List two criteria Mendeleev used in his Periodic Table to classify the elements. State Mendeleev’s Periodic Law and explain why no fixed position was assigned to hydrogen in Mendeleev’s Periodic Table.
Ans:
- Increasing Atomic mass.
- Similar properties in a group.
- The physical and chemical properties of an element are periodic function of their atomic mass.
- No fixed position to Hydrogen because it resembles both alkali metals / group 1, as well as halogen /group 17
(b) How and why does the atomic size of elements vary as we move (i) from left to right in a period, and (ii) down a group in the Modern Periodic Table ?
Ans: (i) Atomic size of elements decrease as we move from left to right across a period as effective Nuclear charge increases
(ii) Increases down a group as number of shells increases.
20) A person is unable to see objects distinctly placed within 50 cm from his eyes.
(a) Name the defect of vision the person is suffering from and list its two possible causes.
Ans: Hypermetropia / farsightedness
Causes:
i.) Shortening of eyeball
ii.) Curvature of eye lens decreases / focal length of eye lens increases.
(b) Draw a ray diagram to show the defect in the above case.
Ans:
(c) Mention the type of lens used by him for the correction of the defect and calculate its power. Assume that the near point for the normal eye is 25 cm.
Ans:
Convex lens
1/f=1/v-1/u
=1/(-50cm) -1/(-25cm)
=1/50cm Hence ,f=50 cm=0.5m
There fore power =(1/0.5 )D=2D
(d) Draw a labelled diagram for the correction of the defect in the above case.
Ans:
21) (a) Define electric power. An electrical device of resistance R is connected across a source of voltage V and draws a current I. Derive an expression for power in terms of current and resistance.
Ans: It is the rate at which electrical energy is dissipated or consumed in an electrical circuit is called electric power .
We know
V=W/Q
W=VQ
W/t = VQ/t
P = VI
P = IR.I
P = I2R
(b) Two electric bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to an electric mains of 220 V. Find the current drawn by the bulbs from the mains.
Ans: Bulb I: I=P/V,100W 220V
I1 =100/220A
=5/11A
Bulb II :60W 220V
I2 = 60/220A
= 3/11 A
OR
(a) How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistors R1 , R2 and R3 in series connected to a battery of V volts ?
Ans: the battery and ammeter and a plug key
- Three resistors R1, R2, R3are joined.
- They are connected with
- The ammeter reading is noted.
- Position of ammeter is changed to different position and readings taken each time.
- The reading remain same.
(b) Study the following circuit and find out :
(i) Current in 12 W resistor.
Ans: 1/Rp=1/R1+1/R2
v=IRT
I=6/24=0.25 Ampere
1/R1=1/R1+1/R1
Rt=Rp+12Ω
Rt=24Ω
(ii) Difference in the readings of A1 and A2 , if any.
Ans: Same readings of A1 and A2
SECTION E
22) Write four sequential steps of the procedure of the experiment ‘‘Preparing a temporary mount of a leaf peel to show stomata.’’
Ans:
- Taking out the leaf peel and mount on the slide_
- stain with safranin
- mount with glycerin
- place cover slip and observe under microscope.
OR
In the experimental set-up to show that ‘‘the germinating seeds give out carbon dioxide’’, answer the following questions :
(i) Why do we keep the conical flask airtight ?
Ans: To prevent the entry of oxygen/escape of CO2 / air
(ii) Name the substance kept in the small test tube inside the conical flask. Write its role.
Ans: KOHabsorb CO2 gas
(iii) Why does water rise in the delivery tube ?
Ans: KOH absorb CO2 gas/Partial vacuum created
23) List two observations on the basis of which it may be concluded that the given slide shows binary fission in Amoeba.
Ans:
- Nucleus elongates
- Constriction in cytoplasm / cell membrane
24) A student mixes sodium sulphate powder in barium chloride powder. What change would the student observe on mixing the two powders ? Justify your answer and explain how he can obtain the desired change.
Ans:
- No Change
- In solid form (powder no reaction will take place because H+ /H3O+ (ions) are not available. Na2 SO4 + BaCl2 ->NaCl + BaSO4(white ppt)
OR
(a) Arrange the following metals in the increasing order of their reactivities : Copper, Zinc, Aluminium and Iron
Ans: Cu<Fe< Zn<AI
Deposition of brown colour on iron.
(b) List two observations you would record in your notebook 30 minutes after adding iron filings to copper sulphate solution.
Ans: Blue Colour change is to green.
25) A solution ‘X’ gives orange colour when a drop of it falls on pH paper, while another solution ‘Y’ gives bluish colour when a drop of it falls on pH paper. What is the nature of both the solutions ? Determine the pH of solutions ‘X’ and ‘Y’.
Ans: (i) X- acidic, pH of X is < 7
(ii) Y- basic, pH of Y is >7
26) Study the following ray diagram and list two mistakes committed by the student while tracing it. Rectify these mistakes by drawing the correct ray diagram to show the real position and size of the image corresponding to the position of the object AB.
Ans: Mistakes :F1 and F2 are not equidistant from the optical center of the lens.
OF1 ≠OF2 ; 2OF1 ≠2OF2
Image should form beyond 2F2
Image should be magnified
OR
A student has to trace the path of a ray of light through a glass prism. List four precautions he should observe for better results.
Ans: (i) Prism should be within the boundary all through the experiment .
(ii) Pins should be fixed vertically and the feet of the pins should be observed.
(iii) Protractor should be used correctly .
(iv) Angle shouldbe taken between 30o and 60o to observe the refraction clearly.
(v) Separation between the pins should be kept at least 5cm .
27) Which one of the following is the correct set-up for studying the dependence of the current on the potential difference across a resistor and why ?
Ans:
- Set up A is correct.
- Ammeter should be connected in series whereas voltmeter should be connected in parallel to the resistor across which potential difference is to be measured.
- Positive of voltmeter and ammeter should be connected to the positive of supply voltage.
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)