31/4/1 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Define resistance. Give its S.I. unit.
Ans:
- Resistance is the property of a conductor to resist the flow of charges through it
- ohm (Ω)
2) Name any two elements that are used in fabricating solar cells.
Ans:
- Silicon, silver
SECTION B
3) State laws of reflection of light.
Ans:
- First law: The incident ray, the reflected ray and the normal to the surface at the point of incidence all lie in the same plane.
- Second law: Angle of incidence is equal to angle of reflection.
OR
Define absolute refractive index and express it mathematically.
Ans:
- Refractive index of a transparent medium with respect to vacuum or air is called absolute refractive index.
- Mathematically
- Absolute refractive index of a medium = Speed of light in vacuum or air/Speed of light in vacuum or airn=c/v
4) Draw magnetic field lines around a bar magnet.
Ans:
5) What happens when 5% alkaline potassium permanganate solution is added drop by drop to warm propyl alcohol (propanol) taken in a test tube ? Explain with the help of a chemical equation.
Ans:
Alkaline KMNO4 is an oxidizing agent.
SECTION C
6) 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
7) 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.
8) (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
9) (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.
10) 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
11) A coil of insulated copper wire is connected to a galvanometer. What would happen if a strong bar magnet is
(a) pushed into the coil ?
Ans: Deflection in the galvanometer in one direction.
- Increase in magnetic field associated with coil.
(b) withdrawn from inside the coil ?
Ans: Deflection in the galvanometer in the opposite direction
- Decrease in magnetic field associated with coil.
(c) held stationary inside the coil ? Give justification for each observation.
Ans: Galvanometer shows no deflection
- No changeof magnetic field associated with coil so no induced current in the coil.
12) (a) Write the function of the following in the human alimentary canal :
(i) Saliva
Ans: contains salivary amylase, converts starch to sugar
(ii) HCl in stomach
Ans: HCl in stomach- medium acidic/kills pathogen (germs)
(iii) Bile juice
Ans: Bile-emulsifies fats/neutralizes acidic food in the duodenum
(iv) Villi
Ans: -increases surface area for absorption
(b) Write one function each of the following enzymes :
(i) Pepsin
Ans: digest protein
(ii) Lipase
Ans: Lipase: digest fats
13) (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
14) What is biodiversity ? Why are forests considered as ‘‘biodiversity hot spots’’ ? List two factors responsible for causing deforestation.
Ans:
- The existence of a variety of species of plants and animals.
- Forests are rich in different life forms.
- Urbanisation /Pollution/Overgrazing/Over exploitation/population explosion /any other.
15) How is the method of extraction of metals high up in the reactivity series different from that for metals in the middle ? Why can the same process not be applied for them ? Name the process used for the extraction of these metals.
Ans:
- The Metals high up in reactivity series are very reactive, because of difference in their reactivity.
- Methods of extraction of metals depends on their reactivity.
- Electrolytic reduction followed by electrolytic refining.
SECTION D
16) (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
17) 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:
18) (a) How is the valency of an element determined if its electronic configuration is known ? Determine the valency of an element of atomic no. 9.
Ans: Valency depends on valence electron. It is the number of electrons taken or lost from the valence shell:
Atomic no = 9
Electronic Configuration = 2, 7.
Valency 8-7=1
(b) Given below are some elements of the Modern Periodic Table. Atomic numbers of the elements are given in parentheses : A(4), B(9), C(14), D(19), E(20)
(i) With the help of the electronic configuration, find out which one of the above elements will have one electron in its outermost shell.
Ans: D (2.8.8.1)
(ii) Which two elements belong to the same group ? Give reasons for your answer.
Ans: A (2.2) and E (2.8.8.2) (same valency-2)
(iii) Which one of the above elements belonging to the fourth period has bigger atomic radius and why ?
Ans: D has larger radius as the atomic radii shrinks in moving from left to right in the same period due to addition of electrons in the same shell .
19) (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
20) (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
21) (a) List two visible traits of garden pea that Mendel considered in his experiments. How do Mendel’s experiments show that traits may be dominant or recessive ?
Ans: a)Height (tall and dwarf) and Shape (round and wrinkled) of seeds, colour of flower (white and violet)
Tall x Short
F1 – Tt(tall) Both TT and Tt are tall plants ,tt are short plants. Single copy of T is tall hence dominant hence tt are recessive
(b) With the help of a flow diagram, how would you establish that in human beings the sex of a newborn is purely a matter of chance and none of the parents may be considered responsible for a particular sex of a newborn child ?
Ans:
x |
|
Male |
Female |
XY |
XX |
Gametes: X,Y |
X |
Zygote: XX |
XY |
Girl |
Boy |
Sex determination is purely by chance. The fusion of a particular sperm with an egg is purely a matter of chance
SECTION E
22) 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.
23) 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
24) 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 .
25) 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.
26) 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
27) 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
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)