31/3/2 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) When do we say that the potential difference between two points of a circuit is 1 volt ?
Ans: If 1J of work is done to carry 1 coulomb of charge from one point to another.
2) Write various steps of a terrestrial food chain of four trophic levels.
Ans: Plant ———> goat—————->fox—————->lion
(Producers) (Herbivore) (Carnivore) (Top Carnivore)
SECTION B
3) Show the formation of magnesium oxide by the transfer of electrons.
Ans:
4) What is insulin ? Why are some patients of diabetes treated by giving injections of insulin ?
Ans:
- Insulin – A hormone produced in the pancreas which regulates the amount of glucose in the blood
- To reduce the blood glucose level
OR
How is the movement of leaves of the sensitive plants different from the movement of a shoot towards light ?
Ans:
Movement of leaf in sensitive plant |
Movement of shoot towards light |
(i) Movement in response to the stimulus of touch independent of direction of stimulus. | Movement in response to the direction of stimulus. |
(ii) Independent of growth | Growth movement. |
5) A glass prism is able to produce a spectrum when white light passes through it but a rectangular block of same transparent glass does not produce any spectrum. Why ?
Ans: The extent of bending of a light ray at core opposite parallel faces of the rectangular glass slab is equal. Therefore, the emergent ray is parallel to the incident ray. So it cannot produce any spectrum.
SECTION C
6) Explain the ways in which glucose is broken down in absence or shortage of oxygen.
Ans: The first step in the breakdown of glucose. Glucose is converted to pyruvate.
Pyruvate in the absence of O2 may be converted to ethanol, CO2 and energy
Pyruvate in the shortage of O2 may be converted to lactic acid and energy.
7) List four functions of the human heart. Why is double circulation necessary in the human body ?
Ans: Four function of human heart:
- Receives deoxygenated blood from body
- Sends blood to lungs for oxygenation
- Receives oxygenated blood from lungs
- Pumps oxygenated blood to different parts of body ( or complete functioning of heart with correct description)
- To have efficient supply of O2for their high energy needs. Separation of oxygenated and deoxygenated blood.
8) (a) Name the part of human brain which controls
(i) voluntary actions,
Ans: Fore brain / cerebrum
and
(ii) involuntary actions.
Ans: Hine brain / medulla oblongata
(b) Write the function of peripheral nervous system. Name the components of this system stating their origin.
Ans: PNS helps in facilitating the communication between
- Cranial Nerves – Brain
- Spinal Nerves – Spinal Cord
9) Explain the following :
(a) Speciation
Ans: Speciation: It refers to the process by which new species are formed from the pre-existing species
i) Geographical isolation
ii) Genetic drift
iii) Natural selection
(b) Natural Selection
Ans: ) Natural selection is the process by which organisms having some special features are at an advantage for better survival in the changed environment.
OR
Mendel, in one of his experiments with pea plants, crossed a variety of pea plant having round seeds with one having wrinkled seeds. State Mendel’s observations giving reasons of F1 and F2 progeny of this cross. Also, list any two contrasting characters, other than round seeds of pea plants that Mendel used in his experiments.
Ans:
- F1 generation – all plants with round seeds
- F2 generation – plants with round and wrinkled seeds.
- Tall / dwarf plants Yellow / green seeds White / purple flowers
10) What is atmospheric refraction ? Explain with the help of a labelled diagram that the position of a star as seen by us is not its true position.
Ans:
- Bending of light due to the variation in optical density of the medium.
- The starlight, on entering into earth’s atmosphere undergoes continuous refraction before it reaches the earth.
- The since the atmosphere bends starlight towards the normal, the apparent position to the star is slightly different from its actual position
Diagram with correct labeling
OR
When do we consider a student sitting in the class to be myopic ? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.
Ans: (i) If the student cannot see the words written on the black board then he is considered myopic.
(ii) The defect may arise due to 1) Excessive curvature of the eyeball 2) Elongation of the eyeball.
(iii)
11) ‘‘Biogas is an excellent fuel.’’ List four reasons to justify this statement. Write the main constituent of this gas and state its percentage.
Ans:
i)It burns without smoke
ii.) Leaves no residue
iii.) Its heating capacity is high
iv.) Efficient method of waste disposal The main constituent of this gas is methane (75%)
12) In a village of South India people started cultivating crops all around a lake. They added fertiliser to their field in order to enhance the yield. Soon after it was discovered that the water body was completely covered with green floating plants and the aquatic animals started dying in large numbers.
Analyse the situation and state reasons for the excessive growth of plants and death of aquatic animals in the lake.
Ans:
- Nutrient rich water from the surrounding fields drain into the lake resulting in high growth of floating plants.
- Layer of floating plants used up the dissolved oxygen and blocked sunlight.
13) Out of three metals P, Q and R, P is less reactive than Q and R is more reactive than P and Q both. Suggest an activity to arrange P, Q and R in order of their decreasing reactivity.
Ans:
Activity |
Observation |
Inference |
Put metal R in the sulphate solution of metal Q and P
Put metal P in the solution of sulphate ions of metal Q |
Solution becomes colourless in both the test tubes.
No reaction |
R displaces P and Q ions from their solutions.
P cannot displace Q ions from the solution |
OR
Name the ore of mercury. With the help of balanced chemical equations, explain the process of extraction of mercury from its ore.
Ans: Cinnabar / (HgS)
2HgS + 3O2 ->2HgO + 2SO2
14) A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound B is also a by-product of chlor-alkali process. Identify B. State the type of reaction that occurs when B is treated with an acidic oxide, say sulphur dioxide. Also write chemical equation for the reaction involved.
Ans: B – sodium hydroxide
It reacts with sulphur dioxide
NaOH+SO2->Na2SO3+H2O (sodium sulphite and water) Neutralization reaction
15) ‘‘Atomic number of an element is considered to be a more appropriate parameter than its atomic mass for a chemist.’’ Take the example of the element X (atomic number 13) to justify this statement.
Ans: Atomic number 13(2, 8, 3) element has electropositive character belongs to group 13 and has valency 3.
SECTION D
16) (a) List four characteristics of the image formed by a convex lens when an object is placed between its optical centre and principal focus.
Ans: i.) Image is formed on the same side of the lens as the object.
ii.) The image is enlarged / magnified, virtual and erect.
(b) Size of the image of an object by a concave lens of focal length 20 cm is observed to be reduced to 3/ 1 rd of its size. Find the distance of the object from the lens
Ans:
ℎ’ =h/3
Focal length = –20cm
As per the lens formula
1/v-1/u=1/f
u = – 40cm
17) a) Three resistors of resistances R1, R2 and R3 are connected (i) in series, and (ii) in parallel. Write expressions for the equivalentresistance of the combination in each case.
Ans:
- In series – RS=R1 + R2 + R3.
- In parallel – 1/Rp=1/R1+1/R2+1/R3
Resistance is at minimum – 1/Rp=1/R1+1/R2
1/12+1/12=2/12=6Ω
Resistance is maximum –Rs= R1+ R2
Rs=12+12=24 Ω
P=v2/R
Power ration in parallel and series = 4:1
(b) Two identical resistors of 12 W each are connected to a battery of 3 V. Calculate the ratio of the power consumed by the resulting combinations with minimum resistance and maximum resistance.
Ans: Pmin/Pmas=V2/Rmin/V2/Rmas=Rmas/Rmin=24=4/1
OR
(a) Write the relation between resistance and electrical resistivity of the material of a conductor in the shape of a cylinder of length ‘l’ and area of cross-section ‘A’. Hence derive the S.I. unit of electrical resistivity.
Ans:
Rαl
Rα1/A
Rα1/A
R=p1/A
p=RA/1=ohm ×m2
=ohm × m
(b) Resistance of a metal wire of length 5 m is 100 W. If the area of cross-section of the wire is 3 ´ 10–7 m2, calculate the resistivity of the metal.
Ans:
p=RA/1
=100 ×3×10-7/5
=60×10-7 ohm×m
18) (a) Name and state the rule to determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.
Ans:
- The rule is Fleming’s left hand rule.
- If the finger points in the direction of the magnetic field and the second finger in the direction of the magnetic field and the second finger in the direction of current then the thumb will point in the direction of motion or the force acting on the conductor
(b) Draw a labelled diagram of an electric motor.
Ans: Electric motor.
19) (a) What is reproduction ? List its two types.
Ans: Reproduction- The process of producing offsprings / young ones of its own kind.
Types:
i) Asexual
ii) Sexual
(b) How are the modes of reproduction different in unicellular and multicellular organisms ?
Ans:
Unicellular Organisms |
Multicellular Organisms |
Only one parent is required | Two parents are required |
It is a fast process of reproduction. | Slower process of reproduction than in unicellular organisms. |
No specialized cells are required for reproduction. | Specialized cells are required for reproduction. |
OR
(a) What are Sexually Transmitted Diseases (STD) ? List two viral and two bacterial STDs.
Ans: STD- A disease that can be transmitted through sexual contact.
- Viral – i)Warts ii) AIDS
- Bacterial- i) Gonorrhoea ii) Syphilis
(b) What is contraception ? List three reasons for adopting contraceptive methods.
Ans: Contraception: The method of preventing unwanted pregnencies, Reasons –
i) To prevent unwanted pregnancies
ii)To control population rise / birth rate
iii)To prevent transfer of STD’s iv)Proper gap between successive births v)For the better health of mother
20) What are structural isomers ? List any four characteristics of isomers. Draw the possible structures of butane.
Ans: The compounds that have identical molecular formula but different structures are called structural isomers characteristics
i) They have some molecular formula
ii) Their structures are different
iii) Different physical and chemical properties.
iv) Same molecular mass and number of atoms.
21) (a) What is a double displacement reaction ? Explain with an example.
Ans: Exchange of ions in a reaction between two.
(b) A small amount of quick lime is added to water in a beaker.
Ans: Na2SO4 + BaCl2 -> BaSO4 + 2 NaCl
(i) Name and define the type of reaction that has taken place.
Ans: (i) Combination reaction: A combination reaction is a reaction where two or more elements or compounds combine to form a single compound.
(ii) Write balanced chemical equation for the above reaction and the chemical name of the product formed.
Ans: CaO + H2O Ca(OH)2
Quick lime Calcium Hydroxide
Chemical name of the product formed
(iii) List two main observations of this reaction.
Ans: Observations of the reactions:
– Reaction takes place vigorously
– Large amount of heat is released.
OR
(a) Design an activity to demonstrate the decomposition reaction of lead nitrate.
Ans: Activity : Take a pinch of lead nitrate powder in a test tube. Heat it over the flame
(b) Draw labelled diagram of the experimental set-up. List two main observations.
Ans:
Observation :
- Emission of brown fumes observed
- Reddish brown colour of residue
(c) Write balanced chemical equation for the reaction stating the physical state of the reactant and the products.
Ans:
SECTION E
22) Consider the scale of a voltmeter shown in the diagram and answer the following questions :
(a) What is the least count of the voltmeter ?
Ans: 0.15V is the least count
(b) What is the reading shown by the voltmeter ?
Ans: The reading shown is 1.8V
(c) If this voltmeter is connected across a resistor of 20 W, how much current is flowing through the resistor?
Ans: R= 20Ω V=1.8V I=v/R =1.8/20=.09amp
23) List in proper sequence the steps of the experiment for determining the approximate focal length of a given concave mirror by obtaining the image of a distant object.
Ans: i) Fix a concave mirror on a stand and place it near a source of bright light
ii) Place a screen fitted on a stand in front of the mirror
iii) Move the screen back and forth, until a sharp and clear image of a distance object line a tree is obtained on the screen
iv) Mark the position of mirror and screen on the scale and note the distance between them
OR
A student has to trace the path of a ray of light passing through a rectangular glass slab for four different values of angle of incidence. (a) Write two important precautions for this experiment.
Ans: The student should take the following precaution
(a) Precaution –
(i)See that the pins are in a straight line and atleast 3cm apart.
(ii)Angle of incidence should be between 300 to 600 .
(iii) Glass slab should always remain inside the boundary.
(b) List two conclusions the student will draw based on his experiment.
Ans: Conclusion –
(i) The emergent ray is parallel to incident ray
(ii) Lateral displacement takes place.
(iii) Angle of incidence = Angle of emergence
24) List the conclusions you will draw while studying the following properties of ethanoic acid :
(a) Odour
Ans: Odour – it smells like vinegar
(b) Solubility in water
Ans: It is soluble in water
(c) Effect on litmus paper
Ans: Blue litmus to red
(d) Reaction with sodium hydrogen carbonate
Ans: NaHCO3 + CH3COOH -> CH3COONa + H2O + CO2
25) What is observed after about 1 hour of adding the strips of copper and aluminium separately to ferrous sulphate solution filled in two beakers ? Name the reaction if any change in colour is noticed. Also, write chemical equation for the reaction.
Ans:
- Putting Cu strips in FeSO4 — no reaction
- Putting Al strips in FeSO4 — change in colour observed
- Displacement reaction
- Al+FeSO4 -> Al2(SO4)3+Fe
OR
A student wants to study a decomposition reaction by taking ferrous sulphate crystals. Write two precautions he must observe while performing the experiment.
Ans: 1) Do not point the mouth of boiling tube at your neighbours or yourself / point the test tube away from the body
2) Hold the test tube in inclined position
3) Hold the test tube with Tongs
26) In the experiment of preparing a temporary mount of a leaf peel to observe stomata, we use two liquids other than water. Name these two liquids and state when and why these liquids are used.
Ans: a) Saffranin is used to stain the material for better view.
b) Glycerine is used to avoid drying of peel.
OR
List four precautions in proper sequence which we observe while preparing a temporary mount of a leaf peel.
Ans: i) Take a thin peel of leaf on a glass slide.
ii) Stain it with saffranin
iii) Remove extra stain
iv) Put a drop of glycerin and cover it with cover slip
27) A student has set up an apparatus to show that ‘‘CO2 is released during respiration’’. After about 1 hour he observes no change in the water level in the delivery tube. Write two possible reasons for the failure of the experiment.
Ans: i) Conical flask is not air tight.
ii) Freshly prepared solution of KOH not used.
iii) Germinating seeds may be dry.
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)