31/5/2 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) State the S.I. unit of potential difference and name the device used to measure it.
Ans:
- Volt
- Voltmeter
2) List two characteristics of a good fuel.
Ans:
- It is less expensive .
- It produces a large amount of heat.
- It can be stored and transported easily.
- It has high calorific value .
- It is ecofriendly or do notcause pollution .
SECTION B
3) Draw a labelled ray diagram to show the path of the reflected ray corresponding to the ray which is directed towards the principal focus of a convex mirror. Mark the angle of incidence and angle of reflection on it.
Ans:
(i) draw mirror
(ii) Complete ray diagram
(iii) ∠i and ∠r is labelled
(iv) Arrows marked
4) List four properties of magnetic field lines.
Ans:
i.) The field lines emerge from north pole and merge at south pole.
ii.) The magnetic field lines are stronger at poles.
iii.) The magnetic field lines do not cross /intersect each other.
iv.) The magnetic field lines are closed curves.
5) What is brine ? What happens when an electric current is passed through it ? Write chemical equation for it.
Ans:
- Brine – an aqueous solution of highly concentrated sodium chloride .
- When electric current is passed through an aqueous solution of sodium chloride it decomposes to form sodium hydroxide, chlorine gas and water.
- 2 NaCl (aq) + 2H2O (l) -> 2NaOH (aq) + Cl2 (g) + H2 (g)
OR
List the changes that are observed when dil. HCl is added to a small amount of copper oxide in a beaker. Write balanced chemical equation for the reaction.
Ans:
- Colour of the solution becomes blue – green due to formation of Copper (II) chloride.
- CuO (s) + dil 2HCl (aq) -> CuCl2 + H2O (l)
SECTION C
6) 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
7) Draw the pattern of the field lines of the magnetic field around a current carrying straight conductor passing through and held perpendicular to a horizontal cardboard. State right-hand thumb rule and explain how this rule is useful to determine the direction of the magnetic field in the above case, if the direction of current in the conductor is vertically downwards
Ans:
- If the direction of the current and magnetic field is correctly represented then the marks should be allotted irrespective of completer circuit.
- Right hand thumb rule: If the right hand thumb is representing the direction of current flowing through the straight current carrying conductor, then curl of finger will represent the direction of magnetic field.
- If the direction of current in the conductor is vertically downwards then the direction of the magnetic field lines will be in clockwise direction.
8) An ore on treatment with dil. HCl gives the smell of rotten egg. Name the type of this ore. How can the metal be obtained from its concentrated ore ?
Ans:
- Sulphide Ore
9) 2 g of ferrous sulphate crystals are heated in a dry boiling tube.
(a) List any two observations.
Ans: observations :
i.) changes from green to white.
ii.) 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.
Ans: 2 Cu + O2 -> 2 CuO
(d) How can the black coating on the surface be turned reddish brown ?
Ans: On passing hydrogen gas over the heated material
10) A white powder is added while baking cakes to make it soft and spongy. Name its main ingredients. Explain the function of each ingredient. Write the chemical reaction taking place when the powder is heated during baking.
Ans:
- It consists of sodium hydrogen carbonate and tartaric acid
- Sodium hydrogen carbonate release carbon dioxide gas which makes cakes soft and fluffy and Tartaric acid neutralizes the bitter taste of the salt
11) List in tabular form three differences between blood and lymph.
Ans:
Blood |
Lymph |
1) It is red coloured fluid because it contains RBC (haemoglobin) | 1) It is colourless fluid that do not contain RBC (haemoglobin) |
2) It flows in arteries, veins and capillaries | 2) It flows in Lymph vessels. |
3) It carries absorbed nutrients, O2, CO2 and nitrogenous waste etc. | 3)It carries digested and absorbed fat from intestine. |
4) It consists of Plasma ,RBC, WBC, Platelets . | 4) It consists of Plasma, Proteins and WBC. |
12) Why does the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron take place but not in the reverse direction ? Explain.
Ans:
This flow is unidirectional.
13) How does the creation of variations in a species promote survival ? Explain with the help of an example.
Ans: Depending on the nature of variations, different individuals would have different kinds of advantages which enable them to survive and adapt in their environment.
Example. Suppose there were a population of bacteria living in temperate waters and if the water temperature were to be increased by global warming, most of these bacteria would die, but a few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time. (or any other relevant example).
14) 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.
- Explanation :
(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 ?
=>Since interference will create disturbances in the protected area (National Park) / To maintain the self sustainability 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 again and again.
15) Mention the environmental consequences of the increasing demand for energy. List four steps you would suggest to reduce the consumption of energy.
Ans:
- Global warming, melting of glaciers
- More efficient lighting (CFL or LED)
– Upgrade heating system
– Use of public transport (metro, bus)
– Choosing renewable sources of energy
SECTION D
16) A concave lens of focal length 60 cm is used to form an image of an object of length 9 cm kept at a distance of 30 cm from it. Use lens formula to determine the nature, position and length of the image formed. Also draw labelled ray diagram to show the image formation in the above case.
Ans: f=-60
h=9cm
u=-30cm
Lens formula: 1/v-1/u=1/f
1/v=1/f+1/u
=-1/60+[-1/30]
=-1/60-1/30
1/v=-1-2/60
v=-20cm
m=v/u=-20/-30=2/3
m=h’/h=>h’ = m x h
=2/3 x9
17) 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
18) (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.
->Covalent compounds are bad conductor of electricity as they do not have free electrons .
(ii) have low melting and boiling points.
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’.
->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.
->
Propanal——- CH3CH2CHO
Propanone——- CH3COCH3
(c) How would you bring the following conversions :
(i) Ethanol to ethene
(ii) Propanol to propanoic acid
Ans:
19) (a) Define groups in the Modern Periodic Table. How do valency, atomic size and metallic character vary in a group ?
Ans: Group: In modern periodic table vertical columns are known as ‘Groups’. There are 18 groups.
- Valency – remains same
- Atomic Size – Increases from top to bottom in a group
- Metallic Character – Increases from top to bottom in a group
(b) The atomic number of an element is 14. Examine if this element will have metallic properties or not. Give reason to justify your answer.
Ans: Atomic Number = 14
Electronic Configuration K, L, M
- It is metalloid or semi – metal
- It exhibits some properties of both metals and non – metal.
20) (a) How do the following provide evidences in favour of evolution in organisms ? Explain with an example for each.
(i) Homologous organs
-> Homologous organs, which have similar basic structures but have different functions. e.g. Forelimbs of human and forelimbs of Lizard .
(ii) Analogous organs
-> Analogous organs are those which have different basic structure but perform similar function. e.g. Wings of insect and wings of bat.
(iii) Fossils
Ans: Fossils are remains or impression of the dead animals and plants that lived in the past. e.g. Archeopteryx or any other example
(b) Explain two methods to determine the age of fossils
Ans: Methods to determine the age of fossils:
(i) Relative dating: Fossils which are found closer to the surface are more recent than those in deeper layers.
(ii) Dating Fossils: Detecting the ratios of different isotopes of the same element ( C )in the fossil.
21) (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
SECTION E
22) 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:
23) 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.
24) 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.
25) 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 .
26) 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.
27) 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
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)