CBSE Class 10 Science Previous Year Question Paper 2020 With Solution
Only preparing for your examinations by learning and reading is not enough, or just having continuous reading revisions are not enough, making sure that you write as much as you read is also one of the aspects of a successful student. So students, the correct way is you’ve to learn and revision yourself.
For this reason, We are here to help you to solve CBSE Class 10 Science Previous year question paper. We know that Solving CBSE Previous Year Question Papers play a Vital role in polishing the preparation and confidence of the students. For that, Our expert teacher will help you by providing Solution paper of CBSE Class 10 Science 2020 Paper. Here We briefly discuss the best solution of all the Previous year question paper. In this E-Learning Era, We provides all the Solved paper of Sec A and Sec B related to CBSE Class 10 Science 2020 Previous year question paper. Below We gave all the Solution paper in PDF format –
CBSE 2020 Science Paper
Set-1, Code no. 31/1/1, Series- JBB/1
Science
Section- A
1.) Name a cyclic unsaturated carbon compound.
Ans: The cyclic unsaturated carbon compounds are those which are having cyclic structure with one or more double and triple bonds.
For example: Cyclobutene, cyclopentene, benzene are the cyclic unsaturated carbon compounds.
2.) The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.
Ans:
The change in magnetic field lines in a coil is the cause of induced electric current in it. This phenomenon is called as electromagnetic induction.
3.) The growing size of human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on. Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population.
a) list two common signs of sexual maturation in boys and girls.
b) what is the result of reckless female foeticide?
c) which contraceptive method changes the hormonal balance of the body?
d) write two factors that determine the size of the population.
Ans:
a)
- The following are the common signs of sexual maturation in boys and girls.
- Voice deepening in boys and girls.
- Pubic, underarm or facial hair development in boys and girls.
- Shoulder and chest become broader in boys and mammary glands would be developed in girls.
b)
- The result of reckless female foeticide is that the number of females as compared to males are very low.
- Hence there will be huge imbalance between male and female ration of the population.
c) Oral pills is the contraceptive method changes the hormonal balance of the body.
d) The size of population mainly determined from two factors which are birth rate and death rate.
4.) Human body is made up of five important components, of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture. Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradable, they are get accumulated progressively at each tropic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.
a) Why is the maximum concentration of pesticides found in human beings?
b) Give one method which could be applied to reduce our intake of pesticides through food to some extent.
c) Various steps in a food chain represent:
1) Food web
2) trophic levels
3) ecosystem
4) biomagnification
d) with regard to various food chains operating in an ecosystem, man is a
1) consumer
2) producer
3) producer and consumer
4) producer and decomposer
Ans:
a)
- As human beings are on the topmost position or at highest trophic level and we know that due to the process of biomagnification there will be increase in DDT concentration level as we go from lowest tropic level to highest trophic level.
- Hence maximum concentration of pesticides is found in human beings.
b) In order to reduce our intake of pesticides through food to some extent, we have to use biopesticides with organic farming and we have to decrease the use of artificial pesticides.
c) The various steps in a food chain represent trophic level.
d) With regard to various food chains operating in an ecosystem, man is a consumer.
5.) Calcium oxide reacts vigorously with water to produce slaked lime.
CaO + H2O -> Ca(OH)2
This reaction can be classified as:
A) combination reaction
B) exothermic reaction
C) endothermic reaction
D) oxidation reaction
Which of the following is the correct option.
a) A and C
b) C and D
c) A, C and D
d) A and B
Ans:
- When calcium oxide reacts vigorously with water then slaked lime Ca(OH)2 is produced with the release of large amount of heat.
- Hence this is exothermic reaction and also the combination reaction.
- Thus, answer is d) A and B.
Or 5.) When hydrogen sulphide gas is passed through a blue solution if copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains same in the solution. The reaction is an example of a:
a) Combination reaction
b) displacement reaction
c) decomposition reaction
d) double displacement reaction
Ans:
- When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains same in the solution.
- As here, there is displacement or exchange of ions of two reactants reacting and forms the product.
- Hence this is the double displacement reaction.
- Answer is d) double displacement reaction
6.) In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:
A) exchange of atoms takes place
B) exchange of ions takes place
C) a precipitate is produced
D) an insoluble salt is produced
The correct option is
a) B and D
b) A and C
c) only B
d) B, C and D
Ans:
- Since, when sodium sulphate reacts with barium chloride solution then barium sulphate the insoluble and precipitate is formed with also sodium chloride.
- Hence, in the given reaction exchange of ions takes place, a precipitate is produced and also an insoluble salt is produced.
- Hence, the answer is d) B, C and D.
7.) Baking soda is a mixture of:
a) sodium carbonate and acetic acid
b) sodium carbonate and tartaric acid
c) sodium hydrogen carbonate and tartaric acid
d) sodium hydrogen carbonate and acetic acid
Ans:
- Baking soda is the mixture of sodium hydrogen carbonate and tartaric acid.
- Hence, the correct answer is c) sodium hydrogen carbonate and tartaric acid.
8.) The chemical formula for plaster of Paris is
a) CaSO4.2H2O
b) CaSO4.H2O
c) CaSO4.1/2H2O
d) 2CaSO4.H2O
Ans:
- The chemical formula for plaster of Paris is CaSO4.1/2H2O
- Hence, the answer is c) CaSO4.1/2H2O
9.) The laws of reflection holds true for:
a) plane mirrors only
b) concave mirrors only
c) convex mirror only
d) all reflecting surfaces
Ans:
- The laws of reflection holds true for all reflecting surfaces.
- Hence, the answer is d) all reflecting surfaces.
Or 9.) When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is
a) real
b) inverted
c) virtual and inverted
d) virtual and erect
Ans:
- When an object is kept within the focus of s concave mirror, an enlarged image is formed behind the mirror which is virtual and erect.
- Hence, the answer is d) virtual and erect.
10.) At the time of short circuit, the electric current in the circuit is
a) vary continuously
b) does not change
c) reduces substantially
d) increases heavily
Ans:
- At the time short circuit, the electric current in the circuit is increasing heavily because resistance of the short circuit nearly equal to zero.
- Hence, the answer is d) increasing heavily.
Or 10.) Two bulbs of 100W and 40W are connected in a series. The current through the 100W bulb is 1A. The current through the 40W bulb will be
a) 0.4A
b) 0.6A
c) 0.8A
d) 1A
Ans:
Given that, two bulbs of 100W and 40W are connected in a series then the current through each bulb will be same.
Hence, if current through the bulb 100W is 1A then the current through the bulb 49W will also be 1A.
Hence, the correct answer is d) 1A.
11.) Which of the following is responsible for the substances of underground water?
a) loss of vegetation cover.
b) diversion for high water demanding crops
c) pollution from urban wastes
d) afforestation
Ans:
- Due afforestation the ground water level remains same or may be increases and hence afforestation is responsible for the sustenance of underground water.
- Hence the correct answer is d) afforestation.
12.) Incomplete combustion of coal and petroleum:
A) increases air pollution
B) increases efficiency of machines
C) reduces global warming
D) produce poisonous gases
The correct option is
a) A and B
b) A and D
c) B and C
d) C and D
Ans:
- As incomplete combustion of coal and petroleum increases the air pollution and also produces poisonous gases.
- Hence the correct answer is b) A and D.
For questions numbers 13 and 14, two statements are given- one labelled assertion A and other labelled reason R. Select the correct answer to these questions from the codes a, b, c and d as given below:
a) both A and R are true and R is the correct explanation of the assertion.
b) both A and R are true but R is not the correct explanation of the assertion.
c) A is true but R is false.
d) A is false but R is true.
13.) Assertion A: Esterification is a process in which sweet smelling substance is produced.
Reason R: when esters reacts with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained.
Ans:
- Here the answer is b) Both A and R are the true but R is not the correct explanation of the assertion.
- Because, in Esterification process the ethanoic acids reacts with the ethanol in the presence of some acid catalyst and gives sweet smelling products which are the esters.
- Hence, the correct answer is b).
14.) Assertion A: In the process of nuclear fission, the amount of nuclear energy generated by fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
Reason R: The nucleus of a heavy atom such as uranium, when bombarded with low energy neutrons, splits apart into lighter nuclei and the product nuclei gets converted to tremendous energy.
Ans:
Here the correct answer is a) Both A and R are true and R is correct explanation of the assertion.
Section B
15.) 1g of copper powder was taken in a China dish and heated. What changes takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equation of reactions, the name and the colour of the products formed in each case.
Ans:
- On heating the 1 g of copper powder which is taken in China dish in air, then it reacts with oxygen in air and get oxidised to form the copper oxide which is black in colour.
- The following reaction shows the oxidation of copper in air on heating.
2Cu + O2 -> 2CuO
- Again, when hydrogen gas is passed over this heated substance a visible change is seen in it that means hot copper oxide reacts with the hydrogen gas passed and forms the copper and water as shown in the following chemical reaction.
CuO + H2 -> Cu + H2O
16.) List the important products of the Chlor-alkali process. Write one important use of each.
Ans:
The important products formed in Chlor-alkali process are NaOH, Cl2 and H2.
Uses of NaOH:
- It is used in producing soaps, rayon, papers.
- It also used in products that explode, dyes and also in petroleum products.
- It can be used in metals cleaning and their processing, electrolytic extraction, oxide coating and in electroplating also.
Uses of Cl2 gas:
- It is used as disinfectant as it kills the bacteria.
- In the treatment of drinking water and swimming pool water it is mainly used.
- Also it is used to make PVC also.
Uses of H2:
- It is used in hydrogenation of fats and oils.
- It is used in rocket fuel, in welding also.
- Also it is used in producing HCl and in the reduction of metallic ores.
Or 16.) How is washing soda prepared from sodium carbonate? Give it’s chemical equation. State the type of this salt. Name the the type of hardness of water which can be removed by it.
Ans:
- Washing soda can be prepared from sodium carbonate by its recrystallization.
- The following chemical reaction shows the formation of washing soda from sodium carbonate.
Na2CO3 + 10H2O -> Na2CO3.10H2O
- The washing soda formed is the basic salt.
- Washing soda can be used for removing permanent hardness of water.
17.) 3mL of ethanol is taken in a test tube and warmed gently in a water bath. A 5% solution of alkaline potassium permanganate is added first drop by drop to this solution, then in excess.
a) How is 5% solution of KMnO4 prepared?
b) State the role of alkaline potassium permanganate in this reaction. What happens on adding it in excess?
c) write chemical equation of this reaction.
Ans:
a) To prepare 5% solution of KMnO4 we have to dissolve 5 g of potassium permanganate in 100 ml of water.
b)
- Here the role of alkaline potassium permanganate in this reaction is it acts as oxidizing agent.
- In this reaction, when we add 5% of potassium permanganate drop by drop to a test tube containing 3ml of ethanol and which warmed gently in water bath, the colour of solution disappeared as the coloured permanganate ions of KMNO4 are used to oxidise ethanol.
- But, when excess of KMNO4 is added to test tube the colour of solution doesn’t changes since all ethanol get oxidised and acetic acid is formed.
c) The following chemical reaction shows the above discussed process.
C2H5OH + alkaline KMnO4 + heat -> CH3COOH
18.) A squirrel is in a scary situation. It’s body has to prepare for either fighting or running away. State the immediate changes that takes place in it’s body so that the squirrel is able to either fight or run?
Ans:
- When squirrel is in s scary situation, it’s body has to prepare for either fighting or running away. Then in that scary situation, in squirrel adrenalin hormone is secreted which brings immediate changes in the body of squirrel which are discussed as below:
- The blood pressure of squirrel increases.
- Heartbeats also increases.
- And more glucose will be released in the blood.
Or 18.) Why is chemical communication better than electrical impulses as a means of communication between cells in a multi cellular organisms?
Ans:
- Chemical communication is better than electrical impulses in multi cellular organisms because it brought through hormones which may diffuse to different parts of body and also it brings communication in cell without any physical interaction. Because this type of chemical communication there will be constantly it would be going and can be easily regulated.
- Hence, chemical communication is better than electrical impulses.
19.) Define the term pollination. Differentiate between self pollination and cross pollination. What is the significance of pollination?
Ans: Pollination is the process in which pollen grains are transferred from anther to stigma of a flower of plant.
Self pollination:
- Self pollination is the process of pollination in which pollen grains are transferred from anther to stigma of the same flower which are genetically similar.
Cross pollination:
- Cross pollination is the process of pollination in which pollen grains are transferred from anther to stigma of flowers which are of different species.
Following is the significance of pollination:
- The main significance of the pollination is that it brings the fertilization in plants.
- Due to cross pollination, we can produces plants with different variation since different genes get mixed.
- And most significant point is that, due to cross pollination some adaptations towards the environment will be developed in plants.
20.) What are homologous structures? Give an example. It is necessary that homologous structures always have a common ancestor. Justify your answer.
Ans:
- Homologous organs or structures as name indicates, these are the organs which are having same origins but they performs the different functions.
- Wings in birds and the forelimbs in human beings are performing the same function but they have the same origins that means they are having similar skeletal structures.
- And it is necessary that homologous structures always have a common ancestor. Because during development of homologous structures they are having same functions but during their adult condition the homologous structures performs the different functions since they would be adapted to different changes towards environment after well development.
21.) Why is Tyndall effect is shown by colloidal particles? State four instances of observing the Tyndall effect.
Ans:
- Tyndall effect is shown by colloidal particles as these particles are having size which is comparable to the wavelength of light and hence when light is passed through the colloidal particles solution it get scattered in all directions.
Following are the four instances of observing Tyndall effect:
- The blue colour of the sky is due to Tyndall effect.
- When light is passed through the milk then Tyndall effect would be observed because milk particles are acts as colloidal particles.
- In fog also, Tyndall effect is observed.
- When we have passed the light through small hole in a room filled with smoke.
Or 21.) Differentiate between a glass slab and a glass prism. What happens when a narrow beam of a) monochromatic light and b) white light passed through
1) glass slab
2) glass prism
Ans:
Glass slab:
- Glass slab is made from glass and it is having rectangular shape.
- When light is passed through the glass slab from air then direction of incident ray and the emergent ray will be parallel to each other.
Glass prism:
- Glass prism is also made from glass, and it has one rectangular base, two triangular sides and two inclined rectangular sides also.
- When we pass a light through prism from air then the incident ray and the emergent will not be parallel to each other.
a) Monochromatic light:
1) When a beam of monochromatic light is passed through glass slab then there will be deviation in path of light ray takes place but the emerging ray is parallel to incident ray as discussed earlier.
2) Now, when the monochromatic light is passed through the glass prism it’s actual path get deviated but after emerging through the glass prism the emergent ray will not be parallel to the incident ray.
b) White light:
1) When a white light is passed through the glass slab then the incident ray and the emerging ray will be parallel to each other.
But there is no spreading of white light into its constituents colours takes place.
2) When white light is passed through the glass prism then the emerging ray is not parallel to the incident ray but there is a spreading of white light into its 7 constituents colours takes place which is called as dispersion of light.
22.) Draw a labelled diagram to show
a) reddish appearance of the sun at the sunrise or the sunset and
b) white appearance of the sun at noon when it is overhead.
Ans:
a) The following figure shows the reddish appearance of the sun at sunrise or sunset.
And the white appearance of the sun at noon when it is overhead.
23.) A V-I graph for a nichrome wire is given below. What do you infer from this graph? Draw a labelled circuit diagram to obtain such graph.
- From the given V-I graph it is concluded, as the graph is straight line passing through origin hence we can say that the slope of the graph is constant throughout.
- Here, the slope of the graph is nothing but the resistance of the wire which is constant throughout.
From slope of graph,
Slope = R = ∆V/∆I = 0.8/0.2= 8/2 = 4 ohm
- Thus, the resistance of the nichrome wire is 4 ohm and which is constant throughout.
- Also, it is conclude that nichrome wire obeys Ohm’s law and hence acts as a ohmic conductor.
- Hence, the circuit diagram representing the above graph is as shown in figure below.
24.)
a) write the mathematical expression for Joule’s law of heating.
b) compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40V.
Ans:
a) Joule’s law of heating gives the heating effect of an electric current.
According to Joule’s law of heating the heat produced in a resistor R is directly proportional to
- Square of the current I through the resistor R.
- Resistance R for a given current.
- Time t for which the current flows through the resistor.
Thus mathematically Joule’s law of heating is given by,
H= I2*R*t
Where H is the heat produced.
b) Given that,
Charge = 96000 C
Time t= 2hrs = 2*60*60= 7200 seconds
Potential difference V= 40 V
Here, I = charge / time = 96000/7200= 13.34 A
We know that, heat generated is given by
H= VIt = 40*13.33*7200
= 3,839,040 J
= 3.84*106 J
Section C
25.) Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with the chemical equations.
Ans:
- The metals sodium, magnesium and aluminium are very reactive metals and hence on reacting with oxygen they forms the strong metal oxides.
- Carbon cannot reduce these strong oxides of sodium, magnesium and aluminium to their respective metals because carbon is low reducing agent.
- These reactive metals are placed in the upper or top position in the periodic table in the reactivity series.
- By the process of electrolytic reduction pure metals are obtained from the oxides of the these reactive metals.
For example:
- The more reactive metal oxide like aluminium oxide undergoes electrolytic reduction in which graphite electrodes are mainly used as anode while the cathode is in the electrolytic chamber.
- And then pure aluminium is deposited on the cathode while the oxygen get attracted towards the anode.
- Thus the reaction that takes place at cathode will be discharge of aluminium at cathode through its reduction.
Al+3 + 3e- -> Al
- And the reaction takes place at anode is the oxidation through which oxygen is evolved.
2O2- -> O2 + 4e-
26.) The position of the certain elements in the modern periodic table are shown below. Using the above table answer the following questions giving reason in each case.
1) which element will form only covalent compounds?
2) which element is a non metal with valency 2?
3) which element is a metal with valency 2?
4) out of H, C and F which ahs largest atmoic size?
5) to which family does H, C and F belong?
Ans:
- The element Si , here is E is the element which has valency 4 and by sharing these 4 electrons with other 4 electrons form the stable compound.
- Hence Si is the element will form only covalent compounds.
2)
- Oxygen is the element having valency 2, here is B and it has high electronegativity due to which prefers to attracts the electrons and not to donate the electrons.
- Hence, oxygen is the non metal with valency 2.
3)
- The metal Mg is the metal with valency 2, here it is the D.
- As Mg has low electronegativity hence it prefers to donate the electrons and attains the stability.
- Hence, Mg is the metal here with valency 2.
4)
- The element F is having largest atmoic size than elements H and C because it’s atmoic radius is greater according to its electronic configuration.
5)
- The elements H, C and F from table belongs to the 18th group of periodic table in which all the elements are stable as their outermost Valence shell is completely filled.
- As their octave is complete and they become stable hence doesn’t reacts with other elements and hence has low tendancy to react with other elements.
- The group 18th elements belongs to the Noble gas family.
Or 26.) Define atomic size? Give it’s unit and measurement. In the modern periodic table what trend is observed in the atomic radius in a group and in a period and why is it so?
Ans:
- The distance between centre of nucleus to the outermost Valence shell of an atom is called as the atomic radius.
- Atomic radius is measured in A°.
- 1A° = 10-10meter
- In the modern periodic table, as we go from too to bottom in a group then we observe that there will be increase in atomic radius because from to bottom in a group the number of valences shell increases due to which atomic radius also increases.
- While as we go from left to right in a period then we observe that atmoic radius decrease because from left to right the atomic number increase indirectly the number of protons in the nucleus also increases and hence effective nuclear charge increases due to which outermost valence shell is binds closely to the nucleus.
- Thus, atomic radius decreases from left to right in periods.
27.) a) why there is a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.
b) Draw a diagram of human respiratory system and labels- pharynx, trachea, lungs, diaphragm and alveolar sac on it.
Ans:
a)
- there is a difference in the rate of breathing between aquatic and terrestrial organisms because aquatic animals get oxygen which is dissolved in water for their breathing.
- And main thing is that the amount of oxygen dissolved in water is very low as compared to the oxygen present in air for terrestrial organisms.
- Hence, the rate of breathing in aquatic animals is more than in terrestrial organisms.
b) Following is the neat labelled diagram of human respiratory system.
Or 27.)a) Name the organs that forms the excretory system in human beings.
b) Describe in brief how urine is produced in human body.
Ans:
a) The organs that forms excretory system in human beings are pair of kidneys, a pair of ureter, a urinary bladder and a urethra.
b) The following is the description of formation of urine in human body:
- In kidney there is a bundle of thin walled blood capillaries and each capillary bundle in the kidney is associated with the cup shaped ending of coil tube called as Bowman’s capsule which helps in collecting the filtrate.
- Each kidney is having large number of these filtratation units called as nephrons or uriniferous tubules.
- Some substances in initial filtrates like glucose, amino acids, salts and large amount of water are selectively reabsorbed when urine flows along the tube.
- And this selective reabsorption depends on the how much excess of water is available in the body and how much amount of dissolved waste has to be excreted.
- The urine formed in each kidney enters the long tube called as ureter which is the connection between kidney and urinary bladder.
- Urine is stored inside the urinary bladder till the pressure of bladder will not be increased to pass it through urethra.
- As the bladder is muscular it is under the nervous control and after that the urine is excreted through the urethra.
28.) a) What is the law of dominance of traits? Explain with an example.
b) why are the traits acquired during the lifetime of an individual not inherited? Explain.
Ans:
a) According to law of dominance, in a hybrid condition the allele which expresses it’s character over the other allele is the dominant allele.
For example:
- When homozygous dominant allele RR is crossed with the homozygous recessive allele rr.
- RR is the dominant character showing round pea plant seed and rr is the recessive character showing wrinkled pea plant seed.
- Then after fertilization, the F1 generation is having both the characters. But the R character is expresses over the r allele.
- And hence the dominant allele here is the R showing round pea seed.
- The following figure explains the law of dominance in pea plants.
b)
- Since acquired traits are those traits which are acquired by the individual during their lifetime. And the traits acquired during the lifetime of an individual are not inherited because these changes in somatic cells and hence cannot be passed to the next progeny.
- This is the main reason behind the non inheritance of the individual while traits acquired during the lifetime.
29.) Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed :
1) between optical center and principal focus of the convex lens.
2) anywhere in front of concave lens.
3) at 2F of a convex lens.
State the signs and values of magnification in the above mentioned cases 1) and 2).
Ans:
1)
- When the object is placed between optical center and principal focus of the convex lens as shown in figure then the image formed will be virtual, magnified and erect due to which the sign of magnification will be positive.
- As the image formed is magnified and hence the absolute magnification is greater than 1.
2)
- when the object is placed anywhere in front of the concave lens as shown in figure then the image formed will be virtual, diminished and erect and hence the sign of magnification will be positive.
- As the image formed is diminished the value of absolute magnification is less than 1.
3) When the object is placed at 2F of a convex lens as shown in figure then the image formed will be of the same size, real and inverted.
Or 29.) An object 4cm.in size, is placed 25 cm in front of the concave mirror of focal length 15cm.
1) at what distance from the mirror should a screen be placed in order to obtain a sharp image?
2) find the size of the image?
3) draw a ray diagram to show the formation of image in this case.
Ans:
Given that,
For a concave mirror:
Object height h1 =4cm
Object distance u= -25cm
Focal length f = -15cm
1) By using mirror formula,
1/f = 1/u + 1/v
1/-15= 1/-25 + 1/v
Thus, 1/v = 1/25 – 1/15=
5/v = 1/5 – 1/3 = (3-5)/15 = -2/15
Thus, 5/v = -2/15
Hence, v/5= -15/2
v= -75/2 = -37.5 cm
Here, negative sign shows that the image will be formed in front of the mirror.
Thus, the screen should be placed at a distance of 37.5 cm in front of the mirror to get the sharp image.
2) We know that, magnification formula is given by,
m= -v/u= h2/h1
Thus, 37.5/-25= h2 /4
Thus, h2 = -(37.5*4)/25= -6cm
Thus, the image formed will be below the principal axis and having size 6cm.
3) The following diagram shows the formation of image in above case.
30.) a) what is an electromagnet? List any two uses.
b) Draw a labelled diagram to show how an electromagnet is made.
c) state the purpose of soft iron core used in making an electromagnet.
d) list two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.
Ans:
a)
- When a current is passed through the soft iron core which is placed inside the solenoid then that soft iron core behaves like a magnet untill current is passed through it and that magnet formed is called as electromagnet.
- Electromagnets are used in motors, generators, transformers and relays.
- They are also used in electric bells, buzzers, loudspeakers and headphones also.
b) Following diagram shows the how an electromagnet is made.
c) The main purpose of soft iron core using in making electromagnet is that it increases the strength of the electromagnet.
d) The strength of an electromagnet will be increased by fixing the material of the electromagnet in following two ways:
Increase in the number of turns and increase in the current through the coil increases the strength of the electromagnet if the material of electromagnet will be
Here is your solution of CBSE Class 10 Science Previous year question paper 2020
Dear Student, I appreciate your efforts and hard work that you all had put in. Thank you for being concerned with us and I wish you for your continued success.