CBSE 2019 Previous Year Paper Class 10 Science Solution

CBSE Class 10 Science Previous year question paper 2019 With Solution

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31-1-1 Science

Set -1, Code no. 31/1/1, Series- JMS/1

Section A

1.) What is the function of a galvanometer in the circuit?

Ans:

Galvanometer in an electrical circuit is used for measuring or detecting the small electric currents. Galvanometer can be converted into an ammeter to measure large current through the circuit.

2.) Why is an biogas is considered an excellent fuel?

Ans:

  • As biogas is a pollutant free clean fuel and doesn’t produces any residue after production of heat energy.
  • And combustion of biogas is smoke free so that there will be no air pollution.
  • Hence, biogas is considered as an excellent fuel.

Section B

3.) How it can be proved that the basic structure of modern periodic table is based on the electronic configuration of atoms of different elements?

Ans:

  • According to Modern periodic law, the physical and chemical properties of all elements in the periodic table are the period functions of their atomic number.
  • The electronic configuration of particular element decide it’s position in modern periodic table.
  • Mainly the number of Valence electrons of a element decide it’s position in group and period.

For example:

  • Na has atomic number 11 and its electronic configuration is 2,8,1.
  • Here only one electron is in Valence shell hence Na lies in group first and period 3rd as it’s Valence electron lies in third shell.

 

  • Similarly, the atomic number of Be is 4 and hence it’s electronic configuration is 2,2.
  • As it’s Valence electron lies in 2nd shell hence Be lies in 2nd group and 2nd period of modern periodic table.
  • In this way, we can say that the basic structure of modern periodic table is based on the electronic configuration of atoms of different elements.

Or 3.) The electronic configuration of an element is 2,84 state it’s:

a) group and period in the modern periodic table.

b) name and write it’s one physical property.

Ans:

a)

  • Given that electronic configuration of an element is 2,8,4.
  • As it’s Valence electron is in third shell hence given element lies in 14th group and 3rd period.

b)

  • As the given electronic configuration is 2,8,4.
  • Hence, the atomic number of an element is 14 and which is the silicon Si.
  • Pure Si is hard, dark grey, brittle and having octahedral crystalline structure.

4.) Write two different ways in which glucose is oxidised to provide energy in human body. Write the product formed in each case.

Ans:

Following are the two different ways in which glucose is oxidised to provide energy in human body:

1) Aerobic respiration:

  • In aerobic respiration, in the presence of oxygen the glucose molecule get broken into pyruvate which is again broken to form the three CO2 molecules and water.

2) Anaerobic respiration:

  • In anaerobic respiration, in the absence of oxygen the glucose molecule get broken into three carbon atoms and pyruvate.
  • And again pyruvate broken to form ethanol and CO2 molecule.

Thus, these are the two ways through which glucose get oxidised to provide energy in human body.

5.) Define the term power of accommodation? Write the modification in the curvature of the eye lens which enables us to see the nearby objects clearly.

Ans:

Power of accommodation:

  • The ability of the eye lens to adjust its focal length in order to see the objects which are place near or apart from it is called as power of accommodation.
  • When we see the objects near to our eyes then ciliary muscles get contracted due to which there will be increase in curvature of the lens.
  • And hence the eye lens become thicker, due to which focal length of eye lens get decreased and hence we can see the nearby objects clearly.

Section C

6.) 2g of silver chloride is taken in a China dish and the China dish is placed in sunlight for sometime. What will be your observation in this case? Write the chemical reaction involved in the form of balanced chemical equation. Identify the type of chemical reaction.

Ans:

  • When 2g of silver chloride is taken in a China dish and china dish is placed in sunlight for sometime then the silver chloride get decomposed to form silver and chlorine by light.
  • Due to which it silver chloride turns grey in sunlight.
  • The following is the chemical reaction which shows decomposition of silver chloride in sunlight.

2AgCl -> 2Ag + Cl2

 

  • As here the decomposition of AgCl in sunlight takes place, hence this reaction is called as photochemical decomposition reaction.

Or 6.) Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions.

a) Zinc reacts with silver nitrate to produce zinc nitrate and silver.

b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.

Ans:

a)

  • This is a displacement reaction.
  • We know that, in displacement reaction more reactive element displaces the less reactive element.
  • Here, Zn is more reactive which displaces the less reactive Ag and forms the Zinc nitrate and silver as shown in following chemical reaction.

Zn + 2AgNO3 -> Zn(NO3)2 + 2Ag

b)

  • This is the double displacement reaction in which there will be exchange of ions between reactant molecules takes place.
  • Following is the double displacement reaction in which potassium iodide reacts with lead nitrate and forms the potassium nitrate and lead iodide.

2KI + On(NO3)2 -> 2KNO3 + PbI2

 

7.) Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it? When is it called rock salt? How is rock salt formed?

Ans:

  • When HCl and NaOH get reacted together then there will be formation of sodium chloride salt.
  • This is the neutralisation reaction and the product formed sodium chloride is the neutral salt.
  • When NaCl is in the crystalline form then it is called as rock salt.
  • Rock salt is formed when there is evaporation of sea water which contains dissolved Na+ and Cl- ions.

8.) Based on the group valency of elements write the molecular formula of the following compounds giving justification of each:

1) Oxides of first group element

2) Halide of the elements of group thirteen and

3) compound formed when an element A of group 2 combines with an element, B of group seventeen.

Ans:

The elements in a same group are having similar chemical and physical properties due the similar Valence shell electronic structure.

a)

The valency of first group element is 1. Hydrogen is the first group element and oxygen has valency 2.

Hence the oxide formed will be H2O.

b)

The elements of group thirteen are having valency 3 and valency of halogen is 1.

Boron B from thirteen group and halogen Cl then halide formed will be BCl3.

c)

  • The valency of element from group 2 is +2 and the valency of element from group seventeen is -1.
  • Mg is the 2nd group element with valency +2 and Br is the 17th group element .
  • Hence, Mg loses 2 electrons which are accepted by two Br elements and compound formed will be MgBr2.

9.) Write three types of blood vessels. Give one important feature of it.

Ans:

The three types of blood vessels that are present in human body are artery, veins and capillary.

Arteries:

  • Arteries are the vessels which carries blood away from the heart to the various organs of the body.
  • As the blood emerging from heart is under high pressure hence the arteries are having thick and elastic walls.

Veins:

  • Veins collect the blood from different organs and bring it back to the heart.
  • Veins are not having thick walls as the blood in not under pressure but they have valves which allows the blood flow only in one direction.

Capillary:

  • Artery after reaching to organ or tissue get divided into smaller and smaller vessels in order to bring the blood in contact with the all individual cells.
  • The smallest vessels are having walls which are one cell thick called as capillaries.
  • Through this thin walls exchange of material between blood and surrounding cells takes place.
  • Capillaries joins together to form veins which helps in conveying the blood away from tissue or organ.

10.) Trace the sequence of events which occur when a bright light is focused on our eyes.

Ans:

  • When a bright light is focused on our eyes initially it reach the brain where it is detected and a proper stimulus is given to specific organ.
  • Here the brain reverses the stimulus i.e. light through motor neuron to the pupil which then contacts.

Following is the sequence traced:

Receptor -> Sensory neuron -> Brain -> Motor neuron -> Eye -> contraction in eye muscles.

11.) What are plant hormones? Name the plant hormone responsible for the following:

a) Growth of stem

b) Promotion of cell division

c) Inhibition of growth

d) Elongation of cells

Ans:

Plant hormones are the chemicals produced in plants by the plants self in order to regulate their growth, development, reproductive processes and also death.

a) Gibberellins is the hormone responsible for growth of stem in plants.

b) Cytokinins is the hormone responsible for promotion of cell division in plants.

c) Abscissic acid in seeds and auxins in lateral buds are the hormones responsible for inhibition of growth in plants.

d) Auxins is the hormone responsible for elongation of cells in plants.

12.) Name the plant Mendel used for his experiment. What type of progeny was obtained by Mendel in F1 and F2 generations when he crossed the tall and short plants? Write ratio he obtained in F2 generation plants.

Ans:

  • Mendel used a number of contrasting visible characters of garden pea plants.
  • He had taken pea plants with different characters like tall and short pea plant and produced progeny by crossing them and from which he calculated percentage of tall and short progeny.

 

  • When he crossed tall pea plants with dwarf or short pea plants then the progeny obtained in F1 generation was tall as shown in figure.
  • When again F1 plants are self crossed then the plants obtained in F2 generation was three tall plants and one dwarf plant.
  • Hence, the phenotypic ratio of F2 generation was found to be TT: Tt: tt = 1:2:1
  • And the phenotypic ratio of F2 generation was found to be Tall: dwarf= 3:1.
  • The following figure shows the Mendel’s experiment for tall and short pea plants.

Or 12.) List two differences between acquired traits and inherited traits by giving an example of each.

Ans:

Acquired traits:

  • Acquired traits are the somatic variations.
  • The effects of environmental factors, use and conscious efforts may develops the acquired traits.
  • Acquired traits will be develop throughout the life of an individual.
  • For example:
  • Learning of dance, music and muscular body of wrestler.

Inherited traits:

  • Inherited traits are nothing but the genetic variations.
  • The reshuffling of genetic materials and mutation may develop the inherited traits.
  • Generally, inherited traits are transferred from parent to the offsprings.
  • For example:
  • Free earlobe or curly hair are the inherited traits.

13.) What is rainbow? Draw a labelled diagram to show the formation of rainbow.

Ans:

  • A rainbow is the natural spectrum appearing in the sky after a rain shower.
  • After rainfall the sky is clear and clouds are in opposite direction to that of sun, so that sunlight is
  • After raining the atmosphere is filled with small water droplets, and this each drop of water acts as a tiny prism.
  • When the sunlight is passed through this raindrops at right angle then it splits into spectrum of seven colours which we called rainbow.
  • Following figure shows the labelled diagram of formation of rainbow.

14.) How can we help in reducing the problem of waste disposal? Suggest any three methods.

Ans:

We reduce the problem of waste disposal in following ways:

  • Initially we have to separate bio degradable and non biodegradable waste.
  • The biodegradable waste like left food from kitchen, fruits, vegetables can be used for composting.
  • And the non biodegradable wastes like plastics, metal sheets can be reused and recycled further.
  • In this we can overcome the problem of waste disposal.

Or 14.) Define an ecosystem? Draw a block diagram to show the flow of energy in an ecosystem.

Ans:

  • Ecosystem consist of the living and non living organisms and interaction between them.
  • The following figure shows the block diagram of flow of energy in an ecosystem.
  • In which producers are the main source of energy from which energy is transferred to primary consumers then to secondary consumers and finally to tertiary consumers.
  • While transferring energy the ten percent law is used.
  • That means out of the energy available only 10% of it is transferred to the next tropic level and remaining will be dissipated.
  • Thus, from figure 10,000J is the energy available at producers out of which only 1000 is transferred to primary consumers.
  • From primary consumers only 100J energy will be transferred to secondary consumers and from it only 10J energy is transferred to tertiary consumers.
  • The following figure shows the block diagram of energy flow in an ecosystem.

15.) What is water harvesting? List two main advantages associated with water harvesting at the community level. Write two causes for the failure of sustained availability of groundwater.

Ans:

  • Water harvesting is the process in which rainwater is collected directly and it can be used for direct use or can be recharged into groundwater.
  • Following are the advantages of associated with water harvesting at the community level:
  • It recharges groundwater and mitigates floods and droughts.
  • It brings rivers and wells back to the life and helps in making more water available.

Following are the causes for the failure of sustained availability of groundwater:

  • The increase in agricultural activities and modern techniques may cause the decrease in groundwater level.
  • Also, industrialization and increase in population are also indirectly responsible for decrease in groundwater level.

Section D

16.) a) List in tabular form three chemical properties on the basis which we can differentiate between a metal and non metal.

b) Give reasons for the following.

1) Most metals conduct electricity well.

2) The reaction of iron (III) oxide [Fe2O3] with heated aluminium is used to join cracked machine parts.

Ans:

Metals:

  • Metals are more reactive and hence they reacts with water to produce metal hydroxide and H2 gas.
  • Metals such as Na, K, Ca and Mg reacts with hydrogen and forms the ionic hydrides while all the other metal doesn’t reacts with H2.
  • Metals on reacting with O2 forms the basic metal oxides.

Non metals:

  • Non metal doesn’t reacts with water to produce H2.
  • While non metals reacts with H2 and forms the covalent hydrides.
  • Non metal reacts with O2 to form the neutral and acidic oxides.

b)

1)

Metals are good conductors of electricity because in metals large number of free electrons are available for conduction and by applying some small amount of energy or potential we can easily get the condition of electricity.

Because of this reason metals are good conductors of electricity.

2)

The reaction of iron (III) oxide [Fe2O3] with heated aluminium is the exothermic reaction in which heat is evolved due which molten metal is generated and which can be used easily to join cracked machine parts.

17.) Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List it’s two uses. Write chemical equation and the name of the product formed when this compound reacts with

a) Sodium metal

b) hot concentrated Sulphuric acid

Ans:

  • The compound which is the active ingredient of the all alcoholic drinks is the ethanol having Chemical formula as CH3-CH2-OH.
  • Ethanol is mainly used in manufacturing of drugs, plastics, lacquers, polishes and in cosmetics also.
  • Also it is used as good fuel in spark ignition engines.

a)

When ethanol reacts with sodium metal then sodium ethoxide is formed with the release of H2 gas as shown in following chemical reaction.

CH3-CH2-OH + Na -> CH3-CH2-Na + H2

b)

When ethanol is recated with hot concentrated Sulphuric acid then ethene and water will be formed as shown in following chemical reaction.

CH3-CH2-OH + conc. H2SO4 -> C2H4 + H2O

Or 17.) What is methane? Draw it’s electron dot structure. Name the type of bonds formed in this compound. Why are such compounds:

a) poor conductors of electricity and

b) have low melting and boiling point? What happens when this compound burns in oxygen?

Ans:

  • Methane is the hydrocarbon which is colourless and odourless , which is inflammable also.
  • As methane is produced after natural decomposition of vegetation in marshlands and hence it is also called as marsh gas.
  • The electron dot structure of methane is as follows.
  • All the bonds i.e. C-C and C-H bonds in methane are the covalent bonds only.

a.)

  • Methane is a poor conductor of electricity because all the electrons in methane are used in forming covalent bond and hence no free electron is available for conduction.
  • Thus, methane is poor conductor of electricity.

 

b)

  • As we know that, in all covalent compounds there is a low intermolecular force of attraction between the molecules due to which these compounds are having low melting and boiling point.
  • As in methane all are covalent bonds having low intermolecular force of attraction hence it also has the low melting and boiling point.
  • When methane burns in oxygen then it forms the CO2 gas and water.

18.) Define pollination. Explain the different types of pollination. List two agents of pollination? How does suitable pollination leads to fertilization?

Ans:

Pollination is the process in which pollen grains are transferred from anther to stigma of a flower of a plant.

Pollination occurs in following two ways:

1) 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.

2) 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.

  • The two main agents of pollination are insects and wind which helps in pollination in flowers.
  • In the process of pollination the pollen grains reaches to the stigma of flower from which pollen tube will be developed.
  • After the formation of pollen tube there will be two gametes are formed one gamete fuses with the egg and forms the diploid zygote while the other one gamete fuses with the polar nuclei and forms the triploid nucleus and it get developed into the endosperm.
  • In this way, the suitable pollination is responsible for the fertilization in flowering plants.

Or 18.) a) Identify the given diagram. Name the parts 1 to 5.

b) What is contraception? List three advantages of adopting contraceptive measures.

Ans:

b)

  • Contraception is the method in which there is a intentional prevention of conception occured through the use of various devices.
  • Or it is the method to prevent fertilization and pregnancy in female.

The advantages of using or adopting contraceptive measures are as follows:

  • It helps in preventing the unwanted pregnancy.
  • Also helps in controlling family plan and population.
  • Use of contraceptive can prevent the spread of diseases like AIDS and Hepatitis B.

19.) An object is placed at a distance of 60cm from a concave lens of focal length 30 cm.

a) Use lens formula to find the distance of the image from the lens.

b) List four characteristics of the image nature, position, size, erect/inverted formed by the lens in this case.

c) Draw a ray diagram to justify your answer of part b)

Ans:

a)

Given that,

For concave lens:

Object distance u=-60 cm

Focal length f= -30cm

By lens formula,

1/f = 1/v- 1/u

1/-30= 1/v +1/60

Thus, 1/v = 1/-30 – 1/60 = -3/60= -1/20

Hence, v= -20cm

Hence, we can say that the image will be formed at a distance of 20cm in front of the lens.

b)

The image formed in between focus F1 and optical centre O which is virtual, erect and diminished as shown in following figure.

c)

The following figure shows the formation of image in case of concave lens under given conditions.

20.) a) With the help of a suitable circuit diagram prove that the reciprocal of the equivalent resistance of the group of residences joined in parallel is equal to the sum of the reciprocal of the individual resistances.

b) In an electric circuit two resistors of 12ohm each are joined in parallel to 6V battery. Find the current drawn from the battery.

Ans:

a)

In parallel combination of resistors the voltage across each resistor will be same as the voltage applied to the circuit. The effective resistance of parallel combination of resistors is very low due to which high current flows through the circuit. But the current through each resistor is different and their total sum is equal to the total current through the circuit. Because of this advantage the parallel combination is used in domestic wiring to protect the circuit from high currents and to adjust the appliances simultaneously.

Now to infer that the potential difference across each resistor connected in parallel is same let us consider an electric circuit in which three resistors R1, R2 and R3 are connected in parallel and  battery of voltage V is applied across them in a series.

It will be found that, the total current I, is equal to the sum of the individual currents flowing through each resistor.

I = I1 + I2 + I3

Let Rp be the equivalent resistance of the parallel combination of resistors.

By applying Ohm’s law to the parallel combination of resistors,

we can write, I = V/Rp

by applying Ohm’s law to each resistor,

we can write,

I 1 = V /R1 ; I 2 = V /R2 ; and I 3 = V /R3

Thus,

V/Rp = V/R1 + V/R2 + V/R3 or 1/Rp = 1/R1 + 1/R2 + 1/R3

Thus, we have proved that the reciprocal of the equivalent resistance of a group of resistances connected in parallel is equal to the sum of the reciprocals of the individual resistances.

b)

Given that, two resistors of resistance 12 ohm are joined in parallel to 6V battery.

Hence, for parallel combination of resistors,

1/Rp = 1/12 + 1/12 = 2/12

Hence, 1/Rp = 1/6

Thus, Rp = 6 ohm

Thus, the current drawn from the battery is given by,

V = IR

I = V/R = 6/6= 1 A

Thus, the current drawn from the battery will be 1A.

Or 20.) An electric lamp of resistance 20 ohm and a conductor of resistance 4 ohm are connected to a 6V battery as shown in the circuit diagram. Calculate:

a) The total resistance of the circuit.

b) The current through the circuit.

c) the potential difference across the 1) electric lamp and 2) conductor

d) power of the lamp.

Ans:

Given that,

Resistance of the lamp = 20 ohm

Resistance of conductor = 4 ohm

Voltage of battery= 6V

a)

Total resistance of the circuit is the sum of resistance of lamp and resistance of the conductor.

Hence, total resistance = 20 + 4 = 24 ohm

b)

According to Ohm’s Law,

V= IR

Hence, I = V/R = 6/24= 1/4= 0.25A

Thus, the current through the circuit will be 0.25 A

c)

1)

Vla= IRla = 0.25*20= 5V

Thus, potential difference across the lamp will be 5V.

And,

2)

Vc= IRc = 0.25*4= 1V

Thus, the potential difference across the conductor will be 1V.

d)

The power of the lamp is given by,

P= I2 *R = 0.25*0.25*20= 1.25W

Thus, the power of the lamp will be 1.25 W.

21.) What is solenoid? Draw the pattern of magnetic field lines of a) a current carrying solenoid and b) a bar magnet.

List two distinguishing features between the two fields.

Ans:

a)

The following figure shows the pattern of magnetic field lines of a current carrying solenoid.

b)

The following figure shows the pattern of magnetic field lines of a bar magnet.

  • We can change the magnitude of magnetic field produced by solenoid by changing the current through the solenoid.
  • While the magnetic field produced due the bar magnet will remain as it is or constant.
  • The magnetic field outside the solenoid is very small or sometimes negligible as compared to the bar magnet.

Section E

22.) Blue litmus solution is added to two test tubes A and B containing dilute HCl and NaOH solution respectively. In which test tube a colour change will occur will be observed? State the colour change and give it’s reason.

Ans:

  • Given that, test tube A contains dilute HCl and test tube B contains NaOH solution.
  • If we add blue litmus solution to test tube A and B then there will be change in colour occurs only in test tube A.
  • In test tube A after adding blue litmus solution the colour changes from blue to red.
  • And this is because HCl is acid and we know that blue litmus turns to red in acid.

Or 22.) What is observed when 2ml.of dilute HCl is added to 1g of sodium carbonate taken in a clean and dry test tube? Write the chemical equation for the reaction involved.

Ans:

  • When 2ml of dilute HCl is added to 1g of sodium carbonate taken in a clean and dry test tube then CO2 gas is evolved with the brisk effervescence.
  • The following is the chemical equation which shows the reaction involved.

2HCl + Na2CO3 -> 2NaCl + H2O + CO2

23.) In three test tubes A, B and C three different liquids namely distilled water, underground water and distilled water in which a pinch of calcium sulphate is dissolved, respectively are taken. Equal amount of soap solution is added to each test tube and the contents are shaken. In which test tube will the length of the foam lather be longest? Justify your answer.

Ans:

  • Given that, test tube A contains distilled water only, test tube B contains underground water and test tube C contains distilled water in which pinch of calcium sulphate is dissolved.
  • Now, when soap solution is added to test tube A containing distilled water means soft water which doesn’t contains any ions and hence the length of the foam formed in test tube A will be longest.

 

  • When a same amount of soap solution is added to test tube B containing underground water which contains calcium and magnesium ions and it reacts with soap forming salts of fatty acids termed as scum. Scum is insoluble in water due to which the length of the foam formed will be less.

 

  • Now, when a same amount of soap solution is added to test tube C containing distilled water with a pinch of calcium sulphate then there will be formation of Calcium ions which reacts with soap and forms the scum insoluble in water.
  • And hence the foam will be formed with specific length but it’s length is smaller as compared to length of foam formed in test tube A.

24.) A student is observing the temporary mount of a leaf peel under a microscope. Draw a labelled diagram of the structure of stomata as see under the microscope.

Ans:

Following figure shows the structure of stomata as see under microscope.

Or 24.) Draw a labelled diagram in proper sequence to show budding in hydra.

Ans:

Following figure shows the proper sequence of budding in hydra.

25.) In the experimental setup to show that CO2 is given out during respiration, name the substance taken in the small test tube kept in the conical flask. State it’s function and consequences of its use.

Ans:

  • In the experimental setup to show that CO2 is given out during respiration, the substance taken in the small test tube kept in the conical flask is the lime water.

 

  • When CO2 gas is passed through lime water then the lime water turns to milky due to the formation of Calcium carbonate. And hence lime water is used to check the presence of CO2.
  • Because of this reason lime water is used for detecting presence of CO2 released during respiration.

26.) While studying the dependence of potential difference V across a resistor on the current I passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I. He got a straight line graph passing through the origin. What does straight line signify? Write the method of determining resistance of the resistor using this graph.

Ans:

Given that, the student plotted graph between V and I. As the graph obtained is straight line passing through origin that means the resistor is the linear component which obeys Ohm’s law.

The slope of the graph at any point gives the value of resistance at that point.

Because, we know that,

Slope = dy/dx

Here, slope = ∆V/∆I

But, we know that

V= IR

Hence, R= V/I

Thus, slope = R= ∆V/∆I

In this way, we can find the resistance of the resistor from V-I graph.

Or 26.) What would you suggest to a student if while performing an experiment he finds that pointer or needle of the ammeter and voltmeter do not coincide with the zero marks on the scales when circuit is open? No extra ammeter or voltmeter is available in the laboratory.

Ans:

  • While performing an experiment, if the needle of ammeter or voltmeter doesn’t coincides with the zero marks on the scales when circuit is open that means that ammeter and voltmeter are having zero error.
  • Hence, to remove this type of error after recording the values of current and voltage we have to subtract this error form that value.
  • Then only we can get the exact values of current and voltage in ammeter and voltmeter having zero error.

27.) List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.

Ans:

Following are the precautions which should a student have to take while determining the focal length of a given convex lens by obtaining image of a distant object on a screen:

  • Initially, he has to fix the convex lens vertically in the lens holder.
  • The bottom portion of lens and the should be in a line with the measuring scale.
  • He has to record the observations only when sharp image would be formed on the screen.
  • He has not to put any obstacle in the path between lens and screen.

Also See: CBSE 2018 Previous Year Paper Class 10 Science Solution


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