CBSE Class 10 Science — Short Answer Questions

(a) (i) Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why? (ii) Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why? (iii) Define the S.I. unit of electric current. OR (b) (i) How many bulbs of resistance $8\Omega$ each should be connected in parallel combination to draw a current of $2\mathrm{A}$ from a battery of $4\mathrm{V}$? (ii) Name the device used for measuring electric current. How is it connected in a circuit? (iii) State Joule's law of heating.

Given below is a pyramid showing various trophic levels in an ecosystem: (a) From the organisms listed below, identify which one is to be placed at which trophic level? Deer, Grass, Lion, Snake, Rabbit (b) Discuss the reason why primary consumers will have more energy as compared to secondary consumers? (c) Why is the base of the pyramid broad?

(a) The resistance of a wire of 0.01 cm radius and 1.0 cm length is $7\Omega$. Calculate its resistivity. (b) An electric heater is rated 220 V; 11 A. Calculate the power consumed if the heater is operated at 200 V.

(a) Name the substance oxidised and reduced in the following reaction: $\mathrm{ZnO + C\longrightarrow Zn + CO}$ (b) Balance the following chemical reaction: $\mathrm{Pb(NO_3)_2 + KI\longrightarrow PbI_2 + KNO_3}$ (c) Give one example each of electrolytic decomposition and decomposition by sunlight.

A person is unable to read a book placed closer than 1 meter from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.

(a) Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode. OR (b) Write the preparation of following compounds with balanced chemical equation: (i) Baking soda (ii) Bleaching powder (iii) Plaster of Paris

(a) The pattern of magnetic field due to a current carrying wire depends upon the shape made by that wire. Justify. (b) A current carrying straight wire AB is shown in the given diagram. Out of X, Y and Z on which point will the strength of magnetic field be maximum and why?

Give differences between the following: (a) Nephron and neuron (b) Sensory nerve and motor nerve (c) Consumers and decomposers

(a) Describe an activity to show that a current carrying conductor, placed in an external magnetic field experiences a force. (b) Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally towards the front wall from the back wall, is deflected by a strong magnetic field to your right side. Find the direction of the magnetic field.

When an incident ray of light enters in a medium 'X' from medium 'Y', it bends away from the normal. Comment about the following: (a) Speed of light in medium 'X' with respect to the speed of light in medium of 'Y'. (b) Optical density of medium 'X' with respect to the optical density medium 'Y'. Give reason for your answer in each case.

An object of height 6 cm is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine: (a) The distance of image from the optical centre. (b) The height of the image formed.

(A) Observe the given figure and identify the labelled parts P, Q, R and S. OR (B) Which of the plant hormones are responsible for the following processes? (i) Promote cell division (ii) Inhibition of growth (iii) Detection of light (iv) Wilting of leaves

Assertion (A): Bacteria that can withstand heat have better chances of survival in a heat wave. Reason (R): Accumulation of variations in a species increases the chances of its survival in changing environment.

(a) Show a cross between a pea plant having round & green seed with a pea plant having wrinkled and yellow seeds upto $F_2$ generation. (b) Also write down results of $F_2$ generation.

Write the preparation of Baking soda. How does it help in making cakes soft and spongy?

(A) (i) How does the change in curvature of the eye lens helps us in the process of seeing the nearby objects clearly? (ii) State the range of the power of accommodation of a normal human eye. OR (B) Draw a ray diagram to show the correction of eye defect of an old man who can not see an object placed closer than 1 m from his eye, clearly.

(a) Draw the ray diagram for refraction of light through a glass prism and mark angle of refraction and angle of deviation. (b) When the path of a light ray refracted through a glass prism is reversed how will the angle of deviation change? Explain.

Assertion (A): In case of iodine deficiency in our diet, there is a possibility that we might suffer from goitre. Reason (R): One of the symptoms of goitre is swelling of neck.

What happens when (i) potassium iodide solution is added to lead (II) nitrate solution? (ii) zinc is added to copper (II) chloride solution? (iii) hydrogen gas is passed over hot copper (II) oxide? Write balanced chemical equations of the reactions involved in support of your answer.

(a) Why does an electric bulb become dim when an electric heater in parallel circuit is switched ON? (b) How to connect three resistors each of resistance 8 Ω, so that the equivalent resistance of the combination is 12 Ω? Draw diagram of the combination and justify your answer.

(a) Draw the ray diagram for refraction of light through a glass prism and mark the angle of refraction and the angle of deviation. (b) When the path of a light ray refracted through a glass prism is reversed, how will the angle of deviation change? Explain.

(a) Mention the gland and the hormone secreted by it in scary situation in human beings. (b) Write two responses that enable the human body to be ready to deal with such situation.

An object is placed at a distance of $30\text{ cm}$ in front of a convex lens of focal length $15\text{ cm}$. Use the lens formula to determine the position of the image. What will be the size of the image in this case?

What happens when (i) Calcium carbonate is heated? (ii) Silver bromide is exposed to sunlight? (iii) Lead is added to copper (II) chloride solution? Write balanced chemical equations of the reactions involved in support of your answer.

(a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags. (b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies? What is this phenomenon known as?

(A) (a) Give the chemical name and formula of Plaster of Paris. (b) Write the chemical equation of its preparation. (c) Give any two uses of it. OR (B) (a) Name the acid present in ant's sting. (b) Give reason: (i) While diluting an acid, it is recommended that the acid should be added to water. (ii) Baking soda is used as an antacid.

(a) Why does an electric bulb become dim when an electric heater in a parallel circuit is switched ON? (b) How would you connect three resistors, each of resistance $8\,\Omega$, so that the equivalent resistance of the combination is $12\,\Omega$? Draw the diagram of the combination and justify your answer.

(a) State the chemical property in each case on which the following uses of baking soda are based upon: (i) as an anti-acids (ii) as a constituent in making baking powder (iii) in soda-acid fire-extinguishers OR (b) Write chemical equations to show what happens when an acid reacts with a (i) metal (ii) base and (iii) carbonate. Write the name of the main product formed in each case.

Name the blood vessel that brings (i) oxygenated blood (ii) deoxygenated blood, to the human heart. Also name that chamber of the heart which receives deoxygenated blood and state how deoxygenated blood from this chamber is sent to lungs for oxygenation.

A person uses lenses of $+2.0 \text{ D}$ power in his spectacles for the correction of his vision. (a) Name the defect of vision the person is suffering from. (b) List two causes of this defect. (c) Determine the focal length of the lenses used in the spectacles.

The gene combination of purple flowered pea plants is denoted as (WW) and that of white flowered pea plants as (ww), when these two plants are crossed $F_1$ generation is obtained. (a) List two observations made by Mendel in $F_1$ generation plants. (b) Give the (i) percentage of white flowered plants and (ii) ratio of the gene combinations WW, Ww and ww in $F_2$ generation. (c) Write one difference between dominant and recessive trait.

(a) Explain the statement "Potential difference between two points is 1 volt". (b) What do the symbols given below represent in an electric circuit? Write one function of each.

A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below: S.No. | Distance of flame (cm) | Distance of image (cm) 1 | -90 | +18 2 | -60 | +20 3 | -40 | +24 4 | -30 | +30 5 | -24 | +40 6 | -20 | +60 7 | -18 | +90 8 | -12 | +120 Analyse the observation table and on the basis of your analysis only, answer the following questions (without doing any calculations): (a) What is the focal length of the convex lens used? Give reason to justify your answer. (b) Which one of the sets of observations is not correct and why? (c) Draw ray diagram to show image formation for any correct set of observation.

Write balanced chemical equation for the reactions that occur when (a) steam is passed over red hot iron. (b) natural gas is burnt in air. (c) glucose reacts with oxygen in the cells of our body and provides energy.

The power of a lens is $-0.25 D$. Based on this information, find out (a) The type of lens and its focal length. (b) The eye defect for which it may be used as a corrective lens. (c) The nature and size of the image formed by this lens when an object is placed between F and 2F from the optical centre of this lens.

The resistance of a wire of $0.01 cm$ radius is 7 ohms. If the resistivity of the material of the wire is $44 \times 10^{-6} ohm$ meter, calculate the length of the wire.

(a) Write the name and one function of respiratory pigment found in human beings. (b) Why do lungs always contain a residual volume of air? (c) Why is ATP known as energy currency of the living beings?

(a) "The third wire of earth connection is very important in domestic electric appliances." Justify this statement. (b) List two precautions to be taken to avoid the overloading of domestic electric circuits.

(a) Define fertilisation. (b) What happens to Zygote, Ovule, Ovary and Stamens after fertilisation in a flowering plant?

Write chemical formula of washing soda. How is it obtained from baking soda? List two uses of washing soda.

(A) Observe the following diagram showing an experiment to determine the conditions under which a metal 'M' corrodes. List your observations in each of the three cases A, B and C with reason, if the metal 'M' is generally protected against corrosion by the method of galvanisation. OR (B) (a) Show the formation of Aluminium Nitride (AlN) by the transfer of electrons. [At. no. of Al = 13; At. no. of N = 7] (b) "Ionic compounds are solids and are generally brittle and break into pieces when pressure is applied." Give reason to justify the statement.

State two limitations of electrical impulses in multicellular organisms. Why is chemical communication better than electrical impulses as a means of communication between cells in multicellular organisms?

(A) Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation? Balance the following chemical equation: $Zn + H_3PO_4 → Zn_3(PO_4)_2 + H_2$ OR (B) Define a precipitation reaction. Give its example and also express the reaction that occurs in the form of a balanced chemical equation.

The electrical resistivity of three materials A, B and C at $20^{\circ}C$ is given below: Material | Resistivity (Ω m) A | $10^{17}$ B | $44 \times 10^{-6}$ C | $1.62 \times 10^{-8}$ (i) Classify these materials as conductor, alloy and insulator. (ii) Give one example of each of these materials and state one use of each material in the design of an electrical appliance say an electric stove or an electric iron.

The digestion of food in human alimentary canal is a complex process. State the enzyme/salt present in the following and mention their function in the process of digestion: (i) Saliva (ii) Bile Juice (iii) Pancreatic Juice

If we want to obtain a virtual and magnified image of an object by using a concave mirror of focal length $18\text{ cm}$, where should the object be placed? Use mirror formula to determine the object distance for an image of magnification $+2$ produced by this mirror to justify your answer.

What are decomposers? Give two examples. State how they maintain a balance in an ecosystem.

Design an activity to show that metals are good conductors of heat and have high melting points.

(a) "In a food chain energy flow is unidirectional." Give two reasons for the given statement. (b) If 10,000 J energy is available at the producer level, how much energy will be available to the secondary consumers? Give reason to justify your answer.

Consider a rectangular cardboard having two holes P and Q through which a current carrying circular loop has been inserted as shown in the diagram. (a) Make this diagram on your answer sheet and draw three magnetic field lines, one each passing through the points 1 (near P), 2 (at the centre of the loop) and 3 (near Q). (b) List two factors on which the intensity of the magnetic field produced at the centre of the loop depends. (c) Name the rule you will apply to determine the direction of magnetic field produced due to a current carrying straight conductor.

On the basis of the characteristics of the processes given in the brackets in each case, differentiate between the following: (a) Products of breakdown of pyruvate in aerobic and anaerobic respiration in human beings (product(s) of the processes) (b) Respiration and photosynthesis in plants (gas released) (c) Respiration in terrestrial animals and fishes (organs involved)

A pure pea plant having round (R), yellow (Y) seeds is crossed with another pure pea plant having wrinkled (r), green (y) seeds. Subsequently $F_1$ progeny is self-pollinated to obtain $F_2$ progeny. (a) What do the seeds of $F_1$ generation look like? (b) Give the possible combinations of traits in seeds of $F_2$ generation. Also give their ratio. (c) State the reason of obtaining seeds of new combination of traits in $F_2$ generation.

What is a rainbow? Draw a labelled diagram to show its formation.

(a) Common salt is an important raw material for various chemicals of daily use. State in brief the method of preparation of (i) Sodium hydroxide, and (ii) Sodium hydrogen carbonate from common salt. Write balanced chemical equations of the reactions that occur. OR (b) Design an experimental set-up to demonstrate that "Alcohol and glucose contain hydrogen but are not categorised as acids". Also give the reason to justify this fact.

(a) What is a reactivity series of elements? How is it developed? Arrange the following elements as they are arranged in the reactivity series: Aluminum, Calcium, Copper, Lead (b) Write balanced chemical equation to show the reaction of iron (III) oxide ($\mathrm{Fe_2O_3}$) with aluminium.

(a) (i) Define the term decomposition reaction. Write one chemical equation each for decomposition reaction where energy is supplied in the form of heat, light or electricity. (ii) Decomposition of vegetable matter into compost is considered an exothermic reaction. Why? OR (b) Why are decomposition reactions called the opposite of combination reactions? Write one chemical equation each for these two types of reactions mentioning the name of the reactant(s) and the product(s) involved in the reactions.

Write the electron-dot structures of (i) sodium, and (ii) oxygen. Using these structures, show the formation of sodium oxide. Mark the anion and cation present in this compound. (At. No. - Sodium = 11 and Oxygen = 8)

(a) Define hormone. (b) "Hormones should be secreted in precise quantities. We have a feedback mechanism through which this is done." With the help of an example justify the statement.

The lowest part of the ear called earlobe, is closely attached to the side of the head in some of us (Figure 'X'), and not in others, called free earlobe (Figure 'Y'). Attached and free earlobes are two variants found in human populations. The gene for free earlobe is dominant over attached earlobes. (a) A man with attached earlobes marries a woman having free earlobes. $50\%$ of their children have free earlobes and $50\%$ have attached earlobes. Explain the inheritance of this trait and write the trait combinations of the progeny. (b) Write the gene combinations of the father and the mother in the above case.

A convex lens forms an $8.0\ \mathrm{cm}$ long image of a $2.0\ \mathrm{cm}$ long object which is kept at a distance of $6.0\ \mathrm{cm}$ from the optical centre of the lens. If the object and the image are on the same side of the lens, find (i) the nature of the image, (ii) the position of the image, and (iii) the focal length of the lens.

Three resistors of $2\ \Omega$, $3\ \Omega$ and $6\ \Omega$ are connected in (i) series, and (ii) parallel. Draw the arrangements of the resistors and find the equivalent resistance of each arrangement.

Write the essential function performed by ozone at the higher levels of the atmosphere. How is it formed in the upper atmosphere? Write the name of the group of chemicals mainly responsible for the depletion of ozone layer.

Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when the object is placed (i) at infinity and (ii) between infinity and pole P of the mirror.

(a) What are chromosomes? (b) Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms?

(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length $l$ and area of cross-section A. Hence derive the SI unit of resistivity. (b) Why are alloys used in electrical heating devices?

Consider the following electric circuit : Calculate the values of the following : (a) The total resistance of the circuit (b) The total current drawn from the source (c) Potential difference across the parallel combination of $10\ \Omega$ and $15\ \Omega$ resistors

(a) "Displacement reactions also play a key role in extracting metals in the middle of the reactivity series." Justify this statement with two examples. (b) Why can metals high up in the reactivity series not be obtained by reduction of their oxides by carbon?

(a) With the help of an activity, explain the conditions under which iron articles get rusted. OR (b) (i) Name two metals which react violently with cold water. List any three observations which a student notes when these metal are dropped in a beaker containing water. (ii) Write a test to identify the gas evolved (if any) during the reaction of these metals with water.

Plants have neither a nervous system nor muscles, even then they respond to stimuli. For example, the leaves of chhui-mui (touch-me-not) plant when touched begin to fold up and droop. (a) How is the information communicated in "touch-me-not" plants? (b) What enables the plant cells to bring out the observable response? (c) Differentiate the movement mentioned above from the movement of tendrils in a pea plant.

(a) What happens when a bundle of wires of soft iron is placed inside the coil of a solenoid carrying a steady current? Name the device obtained. Why is it called so? (b) Draw the magnetic field lines inside a current carrying solenoid. What does this pattern of magnetic field lines indicate?

Differentiate between food chain and food web. In a food chain consisting of deer, grass and tiger, if the population of deer decreases, what will happen to the population of organisms belonging to the first and third trophic levels?

Mendel crossed pure tall pea plants (TT) with pure short pea plants (tt) and obtained $\mathrm{F}_1$ progeny. When the plants of $\mathrm{F}_1$ progeny were self-pollinated, plants of $\mathrm{F}_2$ progeny were obtained. (a) What did the plants of $\mathrm{F}_1$ progeny look like? Give their gene combination. (b) Why could the gene for shortness not be expressed in plants of $\mathrm{F}_1$ progeny? (c) Write the ratio of the plants obtained in $\mathrm{F}_2$ progeny and state the conclusion that can be drawn from this experiment.

Name the ore of mercury and state the form in which it is found in nature. Write the chemical equations along with the condition required for the reactions involved in the extraction of mercury from its ore.

Taking the example of any two animal hormones along with their gland of secretion, explain how these hormones help (i) in growth and development and (ii) regulate metabolism, in the body.

Study the experimental set- up shown in the diagram and write chemical equation for the chemical reaction involved. Name and define the type of reaction. List two other metals which can be used in place of iron to show the same type of reaction with copper sulphate solution.

(a) Study the diagram given below and answer the questions that follow: (i) Name the defect of vision depicted in this diagram stating the part of the eye responsible for this condition. (ii) List two causes of this defect. (iii) Name the type of lens used to correct this defect and state its role in this case. OR (b) What is dispersion of white light? State its cause. Draw a diagram to show dispersion of a beam of white light by a glass prism.

Why is the conversion of ethanol to ethanoic acid an oxidation reaction? Name the oxidising agent used in this conversion. Write chemical equation for this oxidation reaction. How is this reaction different from the reaction in which ethanol burns in the presence of oxygen?

(a) Explain with the help of a labelled diagram, the process of reproduction in Hydra by budding. Name the cells used for reproduction in this process. OR (b) List two roles of each of the following in human reproductive system: (i) Seminal vesicles and prostate gland (ii) Oviduct (iii) Testis

List two differences between dominant traits and recessive traits. What percentage of pea plants in the $\mathrm{F}_2$ generation were with yellow seeds in Mendel's cross between the pea plants having yellow (YY) and green coloured (yy) seeds?

Define the term power of accommodation of human eye. What happens to the image distance in the eye when we increase the distance of an object from the eye? Name and explain the role of the part of human eye responsible for it in this case.

A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the centre of it. He sprinkles some iron filings uniformly around the bar magnet. Then he taps the drawing board gently and observes that the iron filings arrange themselves in a particular pattern. (a) Why do iron filings arrange in a particular pattern? (b) What does the crowding of iron filings at the ends of the magnet indicate? (c) What do the lines, along which the iron filings align, represent? (d) If the student places a cardboard horizontally in a current carrying solenoid and repeats the above activity, in what pattern would the iron filings arrange ? State the conclusion drawn about the magnetic field based on the observed pattern of the lines.

Write the common name and the chemical name of the compound $\mathrm{CaSO_4\cdot\frac{1}{2}H_2O}$. Write the method of its preparation. Give chemical equation for the reaction, when water reacts with $\mathrm{CaSO_4\cdot\frac{1}{2}H_2O}$.

Study the picture given below showing three food chains (a), (b) and (c) and answer the following questions: (i) Name the type of ecosystems that exist in food chains (b) and (c). (ii) The first trophic level in all food chains are producers. Why? What percentage of solar energy do these producers capture for their use? (iii) Why are the arrows shown in the diagram in one direction only and not vice versa? Justify.

Explain in brief the function of an electric fuse in a domestic circuit. An electric heater of current rating 3 kW; 220 V is to be operated in an electric circuit of rating 5 A. What is likely to happen when the heater is switched 'ON'? Justify your answer with necessary calculation.

(a) State Ohm's law. Write formula for the equivalent resistance $R_p$ of the parallel combination of three resistors of values $R_1$, $R_2$ and $R_3$. (b) Find the resistance of the following network of resistors:

We water the soil but it reaches the topmost leaves of the plants. Explain in brief the process involved.

(a) List two constituents of Central Nervous System (CNS). How are these components protected from injuries? (b) Write two limitations of the use of electrical impulses.

State reasons for the following: (a) Zinc oxide is an amphoteric oxide. (b) Sodium metal is stored in bottle filled with kerosene oil. (c) In the reactions of nitric acid with metals, generally hydrogen gas is not evolved.

Name and explain the phenomenon of light due to which the path of a beam of light becomes visible when it enters a smoke filled room through a small hole. Also state the dependence of colour of the light we receive on the size of the particle of the medium through which the beam of light passes.

(a) State giving reason the reduction process to obtain the following metals from their compounds: (i) Mercury, (ii) Copper and (iii) Sodium. OR (b) State giving reason for the change in appearance observed when each of the following metal is exposed to atmospheric air for some time: (i) Silver, (ii) Copper and (iii) Iron.

(a) Define the term power of accommodation of human eye. Write the name of the part of eye which plays a major role in the process of accommodation and explain what happens when human eye focuses (i) nearby objects and (ii) distant objects. OR (b) Draw a ray diagram to show the formation of a rainbow in the sky. On this diagram mark A - where dispersion of light occurs, B - where internal reflection of light occurs and C - where refraction of light occurs. List two necessary conditions to observe a rainbow.

Draw a diagram to show the pattern of magnetic field lines on a horizontal sheet of paper due to a straight conductor passing through its centre and carrying current vertically upwards. Mark on it (i) the direction of current in the conductor and (ii) the corresponding magnetic field lines. State right hand thumb rule and check whether the directions marked by you are in accordance with this rule or not.

Explain the events that take place once a sperm reaches the oviduct till it becomes a foetus. Write the role of placenta in pregnancy.

It is observed that Calcium on reaction with water floats on its surface. Explain why it happens. Also write a balanced chemical equation for the reaction that occurs. What happens when the aqueous solution of the product of this reaction reacts with Carbon dioxide gas? Write a balanced chemical equation for the reaction.

Draw a labelled diagram to show electrolytic refining of copper. State what happens when electric current is passed through the electrolyte taken in this case.

(a) Give reasons for the following : (i) Alveoli in lungs are richly supplied with blood capillaries. (ii) Respiratory pigment in the blood takes up oxygen and not carbon dioxide. (iii) During anaerobic respiration, a 3-carbon molecule is formed as an end product instead of $\mathrm{CO}_2$ in human beings. OR (b) (i) Name the movements that occur all along the gut in human digestive system. How do they help in digestion ? (ii) Where is bile juice stored in human body ? List two roles of bile juice.

Use of pesticides to protect our crops affect organisms at various trophic levels especially human beings. Name the phenomenon involved and explain how does it happen.

(A) Plants $\rightarrow$ Deer $\rightarrow$ Lion In the given food chain, what will be the impact of removing all the organisms of second trophic level on the first and third trophic level? Will the impact be the same for the organisms of the third trophic level in the above food chain if they were present in a food web? Justify. OR (B) A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function. Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?

Study the diagram given below and answer the questions that follow: (i) Name the defect of vision represented in the diagram. Give reason for your answer. (ii) List two causes of this defect. (iii) With the help of a diagram show how this defect of vision is corrected.

Name and state the rule to determine the direction of a : (i) magnetic field produced around a current carrying straight conductor. (ii) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.