Students can access the CBSE Sample Papers for Class 10 Science with Solutions and marking scheme Set 3 will help students understand the difficulty level of the exam.
CBSE Sample Papers for Class 10 Science Set 3 with Solutions
Time Allowed: 3 hours
Maximum Marks: 80
General Instructions:
(i). This question paper consists of 39 questions in 5 sections.
(ii). All questions are compulsory. However, an internal choice is provided in some questions. A student is expected to attempt only one of these questions.
(iii). Section A consists of 20 Objective type questions carrying 1 mark each.
(iv). Section B consists of 6 Very Short questions carrying 02 marks each. Answers to these questions should be in the range of 30 to 50 words.
(v). Section C consists of 7 Short Answer type questions carrying 03 marks each. Answers to these questions should be in the range of 50 to 80 words.
(vi). Section D consists of 3 Long Answer type questions carrying 05 marks each. Answer to these questions should be in the range of 80 to 120 words.
(vii). Section E consists of 3 source-based/case-based units of assessment of 04 marks each with sub-parts.
Section – A (20 Marks)
Select and write the most appropriate option out of the four options given for each of the questions 1 – 20. There is no negative mark for an incorrect response.
Question 1.
Identify gas A in the following experiment.
(A) Nitrogen
(B) Hydrogen
(B) Hydrogen
(D) Carbon dioxide
Answer:
(B) Hydrogen
Explanation: The gas A is hydrogen as hydrogen gas bums with a pop sound.
Question 2.
Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
(i) Au
(ii) Cu
(iii) Na
(iv) K
(A) (i) and (ii)
(B) (i) and (iii)
(C) (ii) and (iii)
(D) (iii) and (iv)
Answer:
(A) (i) and (ii)
Explanation: Sodium and potassium are extracted by electrolytic reduction. Metals obtained after electrolytic reduction are in pure form. But, copper and gold are in impure form after extraction. Copper and gold are refined by electrolytic refining methods.
Question 3.
A metal ribbon ‘X’ burns in oxygen with a dazzling white flame forming a white ash ‘Y. The correct description of X, Y and the type of reaction is:
(A) X = Ca; Y = CaO; Type of reaction = Decomposition
(B) X = Mg; Y = MgO; Type of reaction = Combination
(C) X = Al; Y = Al2O3; Type of reaction = Thermal decomposition
(D) X = Zn; Y = ZnO; Type of reaction = Endothermic
Answer:
(B) X = Mg; Y = MgO; Type of reaction = Combination
Explanation: X is Mg, Y is MgO and the type of reaction is a combination reaction.
2Mg(X) + O2 → 2MgO(Y), This is an example of a combination reaction.
Question 4.
While studying the saponification reaction, what do you observe when you mix an equal amount of colourless vegetable oil and 20% aqueous solution of NaOH in a beaker?
(A) The colour of the mixture has become dark brown.
(B) A brisk effervescence is taking place in the beaker.
(C) The outer surface of the beaker has become hot.
(D) The outer surface of the beaker has become cold.
Answer:
(C) The outer surface of the beaker has become hot.
Explanation: The beaker becomes hot because it is an exothermic reaction.
Question 5.
The correct electron dot structure of a water molecule is:
Answer:
Explanation: In the electron dot structure, oxygen has a complete octet, while each atom of hydrogen has two electrons in the outermost shell.
Question 6.
Two salts X and Y are dissolved in water separately. When phenolphthalein is added to these two solutions solution X turns pink and solution Y does not show any change in colour, therefore X and Y are:
(x) (y)
(A) Na2CO3 NH4C1
(B) Na2SO4 NaHCO3
(C) NH4Cl Na2SO4
(D) NaNO3 Na2SO4
Answer:
(A) Na2CO3 NH4C1
Explanation: Phenolphthalein gives pink colour in a basic pH range from 8.2 to 10. When phenolphthalein is added to Na2CO3 solution, which is a basic solution, the solution will turn pink in colour. However, when phenolphthalein is added to NH4Cl, which is an acidic solution, the solution will remain colourless.
Question 7.
In which of the following, the identity of initial substance remains unchanged?
(A) Curdling of milk
(B) Formation of crystals by process of crystallisation
(C) Fermentation of grapes
(D) Digestion of food
Answer:
(B) Formation of crystals by process of crystallisation
Explanation: During the formation of crystals by the process of crystallisation, the identity of the initial substance remains unchanged. It merely gets crystallised. However, in the process of curdling of milk, the initial substance which is used gets changed as the milk gets converted into curd. In the fermentation of grapes process, the initial substance, grapes change into an alcoholicbeverage. In the process of digestion of food, the initial substance of food gets digested to give essential nutrition and energy to our body.
Question 8.
In plants the role of cytokinin is:
(A) Promote cell division
(B) Wilting of leaves
(C) Promote the opening of stomatal pore
(D) Help in the growth of stem
Answer:
(A) Promote cell division
Explanation: Cytokinin regulates the cell division by promoting it in the plants.
Question 9.
One of the events that do not occur during photosynthesis is:
(A) Chlorophyll absorbs solar energy.
(B) Carbon dioxide is released during the process.
(C) Oxygen is released during the process.
(D) Carbon dioxide is absorbed during the process.
Answer:
(B) Carbon dioxide is released during the process.
Explanation: During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil. Within the plant cell, the water is oxidised, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose.
Question 10.
Observe the following diagram and identify the process and its significance from the following options:
(A) Evaporation: maintains water contents in leaf cells.
(B) Transpiration: creates a suction force which pulls water inside the plant.
(C) Excretion: helps in excreting out waste water from the plant.
(D) Translocation: helps in transporting materials from one cell to another.
Answer:
(B) Transpiration: creates a suction force which pulls water inside the plant.
Explanation: The loss of water vapour through the stomata present on the surface of leaves is called transpiration. It creates a suction pressure for the upward movement of water in all tall trees.
Question 11.
In an experiment with pea plants, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plant to pure short plants in F2 generation will be:
(A) 1 : 3
(B) 3 : 1
(C) 1 : 1
(D) 2 : 1
Answer:
(C) 1 : 1
Explanation: When a pure tall plant (TT) is crossed with the pure short plant (tt), then the progeny in the Fi generation will be hybrid (Tt). When the F1 generation is self-crossed (Tt), then in the F2 generation, the progeny produced will be tall homozygous (TT), Tall heterozygous (Tt), and dwarf homozygous (tt). Hence, the ratio of pure tall plants to pure short plants in F2 generation will be 1 :1 (TT : tt)
Question 12.
The thread like structures that develop on a moist slice of bread in Rhizopus are:
(A) Sporangia
(B) Filaments
(C) Rhizoids
(D) Hyphae
Answer:
(D) Hyphae
Explanation: Hyphae are the fine thread-like structures of fungi that are spread on the whole surface of a slice of bread.
Question 13.
In torch lights and head lights of vehicles, the bulb is placed:
(A) Between the pole and the focus of the reflector.
(B) Very near to the focus of the reflector.
(C) Between the focus and centre of curvature of the reflector.
(D) At the centre of curvature of the reflector.
Answer:
(B) Very near to the focus of the reflector.
Explanation: Inside a bulb there generally is a concave reflector. For a concave mirror, when an object is placed at its focus, after reflection from the mirror, it reflects a parallel beam of light that goes to infinity. Hence, in torches, searchlights and headlights of vehicles, the bulb is placed very near to the focus of the reflector
Question 14.
The radius of curvature of a converging mirror is 30 cm. At what distance from the mirror should an object be placed as to obtain a virtual image?
(A) Infinity
(B) 30 cm
(C) Between 15 cm and 30 cm
(D) Between 0 cm and 15 cm 1
Answer:
(D) Between 0 cm and 15 cm 1
Explanation: Radius of curvature of converging mirror = 30 cm
To obtain a virtual image, in case of a concave mirror (converging mirror), the object should be between pole and focus.
Using Focal length,f = Radius of curvature Y/2 (OR) f = 30/2 = 15 cm.
Question 15.
Which group of organisms are not constituents of a food chain?
(i) Grass, lion, rabbit, wolf
(ii) Plankton, man, fish, grasshopper
(iii) Wolf, grass, snake, tiger
(iv) Frog, snake, eagle, grass, grasshopper
(A) (i) and (iii)
(B) (iii) and (iv)
(C) (ii) and (iii)
(D) (i) and (iv)
Answer:
(C) (ii) and (iii)
Explanation: Food chain (ii): It is an aquatic food chain so grasshopper cannot be a part of it. In food chain (iii): Wolf, snake and tiger, all are carnivores. There are no herbivores to eat grass; therefore grass cannot be a part of the food chain
Question 16.
Depletion of ozone is mainly due to:
(A) Chlorofluorocarbon compounds
(B) Carbon monoxide
(C) Methane
(D) Pesticides
Answer:
(A) Chlorofluorocarbon compounds
Explanation: Depletion of ozone layer occurs due to chlorofluorocarbons (CFCs). Other chemicals do not cause depletion of the ozone layer in the environment.
Question Nos. 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, and R is not the correct explanation of A.
(C) A is true but R is false.
(D) A is false but R is true.
Question 17.
Assertion (A): Sodium hydrogen carbonate is used as an ingredient in antacids.
Reason (R): NaHCO3 is a mild non-corrosive basic salt.
Answer:
(A) Both A and R are true, and R is the correct explanation of A.
Explanation: Sodium hydrogen carbonate (NaHCO3) is used as an ingredient in antacids because being alkaline, it neutralises excess acid in the stomach and provides relief. It is a mild, noncorrosive salt
Question 18.
Assertion (A): The inner walls of the small intestine have finger like projections called villi which are rich in blood.
Reason (R): These villi have a large surface area to help the small intestine in completing the digestion of food.1
Answer:
(A) Both A and R are true, and R is the correct explanation of A.
Explanation: The inner lining of the small intestine has finger-like projections called villi which increase the surface area for absorption. The villi are richly supplied with the blood vessels which take the absorbed food to each and every cell of the body
Question 19.
Assertion (A): On freely suspending a current-carrying solenoid, it comes to rest in geographical N-S direction.
Reason (R): One end of current carrying straight solenoid behaves as a North pole and the other end as a South pole, just like a bar magnet.
Answer:
(A) Both A and R are true, and R is the correct explanation of A.
Explanation: A current carrying freely suspended solenoid behaves just like a bar magnet. Hence, it rests in the North-South direction exactly in the same manner as a bar magnet does.
Question 20.
Assertion (A): Food chain is responsible for the entry of harmful chemicals in our bodies.
Reason (R): The length and complexity of food chains vary greatly.
Answer:
(B) Both A and R are true, and R is not the correct explanation of A.
Explanation: Through bio-magnification, harmful chemicals that are not metabolised by our body pass into the food chain, irrespective of the length & complexity of the food chain, which may vary in nature.
Section – B (12 Marks)
Question 21.
The industrial process used for the manufacture of caustic soda involves electrolysis of an aqueous solution of compound ‘X’, In this process, two gases ‘Y and ‘Z’ are liberated. ‘Y’ is liberated at cathode and ‘Z’, which is liberated at anode, on treatment with dry slaked lime forms a compound ‘B’. Name X, Y, Z and B.
Answer:
Compound X is NaCl(aq), which is a concentrated aqueous solution of sodium chloride in water.
Compound Y is H2 (hydrogen gas), liberated at cathode.
Compound Z is Cl2 (chlorine gas), liberated at anode.
Treatment of gas Z (Cl2 with dry slaked lime, Ca(OH)2, gives bleaching powder (CaOCl2).
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Hence, Compound B is CaOCl2
The overall balanced chemical equation is: 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Question 22.
There are various muscles present in the human digestive system known as sphincters. Two examples of those are given below:
(a) Pyloric sphincter- at the junction of stomach and small intestine
(b) Anal sphincter- at the anus
Give ONE most likely consequence of malfunctioning of each of these sphincters.
Answer:
Pyloric sphincter. Food will get into the small intestine too fast causing poor absorption.
Anal sphincter: Involuntary release of faeces from the body.
Question 23.
Name the part of brain which is responsible for the following actions:
(a) Maintaining posture and balance
(b) Beating of heart
(c) Thinking
(d) Blood pressure
Answer:
(a) Cerebellum
(b) Medulla
(c) Cerebrum
(d) Medulla
OR
Where are auxins synthesised in a plant? Which organ of the plant shows:
(a) Positive phototropism
(b) Negative geotropism
(c) Positive hydrotropism
Answer:
Auxins are synthesised in the growing regions at the tip of the shoot and root in a plant.
(a) Positive phototropism- Shoot
(b) Negative geotropism- Shoot
(c) Positive hydrotropism- Root
Question 24.
A student traces the path of a ray of light through a glass prism as shown in the diagram but leaves it incomplete and unlabelled. Redraw and complete the diagram. Also label on it ∠i, ∠e, ∠r and ∠D.
Answer:
Labelling of ∠i, ∠e, ∠r & ∠D.
Question 25.
A circuit contains a battery, a variable resistor and a solenoid. The figure shows the magnetic field pattern produced by the current in the solenoid.
(a) State how the magnetic field pattern indicates regions where the magnetic field is stronger.
(b) What happens to the magnetic field when the current in the circuit is reversed?
Answer:
(a) Relative clqseness of field lines indicates the strength of the magnetic field. Since field lines are crowded around the ends of the solenoid, hence these are the regions of strongest magnetism.
(b) The direction of the field will also be reversed
OR
State any two factors on which the magnetic field produced by a current carrying straight conductor depends. Mention the rule which helps to find the direction of its magnetic field.
Answer:
Factors on which the magnetic field produced by a current carrying conductor depends:
(i) Strength of current passing through the conductor.
(ii) Distance of the point of measurement from the conductor.
Right-Hand Thumb rule gives the direction of the magnetic field
Question 26.
DDT was sprayed in a lake to regulate breeding of mosquitoes. How would it affect the trophic levels in the following food chain associated with a lake? Justify your answer.
Answer:
DDT being a non-biodegradable pesticide will enter the food chain from the first trophic level, i.e., Plankton.
Non-biodegradable pesticides accumulate progressively at each trophic level. This phenomenon is known as biological magnification.
Hawk will have the highest level of pesticide.
Section – C (21 Marks)
Question 27.
Consider the following organic compounds:
(a) Name the functional group present in these compounds.
(b) Write the general formula for the compounds of this functional group.
(c) State the relationship between these compounds and draw the structure of any other compound having similar functional group.
Answer:
(a) Functional group: Aldehyde
(b) General formula: CnH2nO
(c) It forms the part of the homologous series of the aldehydes as these compounds differ from each other by -CH2 unit.
Structure of 4th member of this series is:
Question 28.
Distinguish between esterification and saponification reactions with the help of the chemical equations for each. State one use of each (i) esters and (ii) saponification process.
Answer:
Esterification is the process by which esters are formed when an alcohol reacts with an acid in the presence of cone, sulphuric acid.
R’OH + RCOOH H+> RCOOR’ (Ester) + H2O
CH3CH2OH + CH3COOH → + CH3COOC2H5 + H2O
Saponification reaction is when ester reacts with NaOH, to form the sodium salt of acid (soap) and alcohol.
RCOOR’ + NaOH → RCOONa (Soap) + R’OH
CH3COOC2H5 + NaOH → CH3COONa + C2H5OH
(i) Uses of esters: Used in making perfumes, or as artificial flavouring agents in ice-creams and cold drinks.
(ii) Uses of saponification process: Used in making soaps.
OR
Write three different chemical reactions showing the conversion of ethanoic acid to sodium ethanoate. Write balanced chemical equation in each case. Write the name of the reactants and the products other than ethanoic acid and sodium ethanoate in each case.
Answer:
Sodium ethanoate (CH3COONa) can be formed from ethanoic acid in the following reactions:
(i) Reaction with sodium carbonate:
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O (water)
(ii) Reaction with sodium bicarbonate:
CH3COOH + NaHCO3 → CH3COONa + CO2 + H2O (water)
(iii) Neutralisation reaction:
CH3COOH + NaOH → CH3COONa + H2O (water)
Question 29
(a) What is double circulation?
(b) Why is the separation of the right side and the left side of the heart useful?
(c) How does it help birds and mammals?
Answer:
(a) Double circulation is the process during which blood passes twice through the heart during one complete cycle. Blood is circulated to the body tissues through systemic circulation and to the lungs through pulmonary circulation.
(b) The separation of the right side and left side of the heart helps in the separation of oxygenated and deoxygenated blood, which allows a more efficient supply of oxygen to the body cells.
(c) Birdsand mammals are warm blooded animals. Since they require more energy to maintain a constant body temperature; hence, the separation provides the availability of oxygen during respiration to generate more energy for thermoregulation.
Question 30.
Name the phenomenon occurring in plants which are under the control of gravity, water and chemicals with one example each that shows the movement involved.
Answer:
Geotropism: It is the movement of plant parts in response to the direction of gravity. The growth of plant roots is an example of geotropism as it grows towards the direction of gravity.
Hydrotropism: It is the movement of a plant towards the water.
Example: The plant roots always move towards water hence it shows positive hydrotropism.
Chemotropism: It is the movement of plants in response to a chemical stimulus. A classic example\ of this type of movement is the growth of the pollen tube towards the ovule, during fertilisation, in a flower.
Question 31.
(a) What is visible spectrum?
(b) Why is red used as the stopping light at traffic signals?
(c) Two triangular glass prisms are kept together connected through their rectangular side. A light beam is passed through one side of the combination. Will there be any dispersion? Justify your answer.
Answer:
(a) Visible |pectrum is the band of coloured components of a white light beam.
(b) Red light is scattered the leastby air molecules and has a longer wavelength. It travels the longest distance.
(c) The. given setup will behave like a glass dab, resulting in the recombination of the seven colours to produce white ligfit.
Question 32.
(a) State Ohm’s law. Represent it mathematically.
(b) Define 1 ohm.
(c) What is the resistance of a conductor through which a current of 0.5 A flows when a potential difference of 2 V is applied across its ends?
Answer:
(a) Ohm’s law: It states that “Electric current through a metallic conductor is directly proportional to the potential difference across the conductor of the circuit provided that temperature and other physical quantities remain constant.
Mathematical expression for Ohm’s Law:
7 ∝ V.
Or V=IR
Or I = V/R
where, R = constant called resistance of a given metal.
(b) 1 Ohm = When potential difference is 1 V and the current through the circuit is 1 A, then the resistance is1 ohm.
1 Ohm = 1 volt/1 amper
(c) Given, I = 0.5 A
Potential difference, V = 2 V
Applying ohm’s law, V = IR
Or, R = V/1 = 2/0.5 = 4 Ω
Hence, the resistance of a conductor is 4 Ω.
Question 33.
(a) A student wants to use an electric heater, an electric bulb and an electric fan simultaneously. How should these gadgets be connected with the mains? Justify your answer giving three reasons.
(b) What is an electric fuse? How is it connected in a circuit?
Answer:
(a) All these electrical gadgets can be connected in parallel. It is because:
(i) All appliances will get the same potential difference in parallel so the flow of any one appliance is not affected on switching on or off of other appliance.
(ii) In parallel arrangement if one appliance is switched off or fuses, other can effectively work.
(b) Electric fuse is a safety device that protects our electrical appliances in case of short circuit or overloading. It is made up of pure tin or an alloy of copper and tin. It is always connected in series with a live wire.
Section – D (15 marks)
Question 34.
(a) It is observed that covalent compounds are bad conductors of electricity. Give reason.
Answer:
Covalent compounds are bad conductors of electricity because they do not have free electrons or ions that can move and carry an electric current
(b) Carbon can neither form C4+ cation or C4- anion. Why?
Answer:
The atomic number of Carbon is 6 with an electronic configuration of 2, 4. Hence, carbon has 4 electrons in its valence shell. Carbon can lose or gain 4 electrons in order to gain stability. It cannot gain four electrons as carbon atom having 6 protons is very small to handle 10 electrons and it cannot donate electrons as it needs a lot of energy to do so. Hence, it cannot form C4+ cation or C4- anion anion and thus forms a covalent bond
(c) Draw electron dot structure of ethanol.
Answer:
The electron dot structure of Ethanol is:
(d) Identify heteroatom(s) in the following compounds:
Answer:
Heteroatoms are the elements that replace hydrogen in a hydrocarbon
Answer:
(a) Oxygen
(b) Chlorine
OR
(a) What are soaps? Explain the mechanism of cleansing action of soap with the help of a labelled diagram.
Answer:
Soaps are the sodium or potassium salts of long-chain fatty acids. They are formed by the reaction between an alkali (sodium hydroxide or potassium hydroxide) and a fat or oil.
Cleansing action of soap:
(i) The long hydrocarbon chain of the soap is non-polar and tends to avoid water. When soap is added to water, the hydrophobic tail is attracted to the dirt, oil or grease, while the hydrophilic head is attracted to the water molecules.
(ii) The hydrophobic tail surrounds the oil or grease droplet, forming a sphere called a micelle.
(iii) The soap molecules on the outside of the micelle are attracted to the water molecules and are washed away with the water, carrying the micelle and dirt along with it.
(iv) When the soap and water are rinsed off, the dirt, oil, and grease are removed from the surface
(b) Detergents are better than soaps. Justify.
Answer:
Detergents are better than soaps as:
(i) Detergents work better in hard water than soaps as they do not react with the minerals in hard water to form insoluble compounds.
(ii) Detergents can be used in both hot and cold water, whereas soaps work better in hot water.
(iii) Detergents are more effective in removing grease and oil stains than soaps.
(iv) Detergents are less likely to leave a residue on clothes, unlike soaps
Question 35.
(a) Name the two types of pollination and differentiate between them.
Answer:
The two types of pollination are self pollination and cross pollination.
(i) Self pollination: When the pollen grains from the stamens of a flower fall on the stigma of the same flower, then self pollination occurs.
(ii) Cross pollination: When pollen grains from the stamens of a flower fall on the stigma of another flower, then cross pollination occurs
(b) Explain the post fertilisation changes that occur in the ovary of a flower.
Answer:
(b) Post-fertilisation changes that occur in the ovary of a flower are:
(i) The fertilised ovule forms a seed.
(ii) The seed contains an embryo, enclosed in a protective covering, called the seed coat.
(iii) As the seed grows further, other floral parts wither and fall off.
(iv) This leads to the growth of the ovary, which enlarges and ripens to become a fruit with a thick wall called the pericarp.
(c) Given below is a diagram of a germinating seed. Label the parts that:
(i) Gives rise to future shoot.
(ii) Gives rise to future root system.
(iii) Stores food.
Answer:
(i) The part labelled as A is plumule, which gives rise to future shoot.
(ii) The part labelled as B is radical, which gives rise to future root.
(iii) The part labelled as C is cotyledon, which stores food
OR
(i) Name and explain the two modes of asexual reproduction observed in Hydra.
Answer:
The two modes of asexual reproduction observed in Hydra are: Budding and regeneration.
Budding in Hydra: In budding, a small part of the body of the parents grows out as a ‘bud’ which then detaches and becomes a new organism. Hydra reproduces by budding using the regenerative cells. A bud develops as an outgrowth in Hydra due to repeated cell division at one specific site. When fully mature, the bud detaches itself from the parent body and develops into new independent individuals.
Regeneration in Hydra: In this method, small cut or broken parts of the organisms’ body grow or regenerate into separate individuals. Regeneration of Hydra from the body parts is carried out by specialised cells, which proliferate and make a large number of cells.
(ii) What is vegetative propagation? List two advantages of using this technique.
Answer:
Vegetative propagation is the development of a new plant from the vegetative parts (roots, stem and leaves) of a plant.
Advantages:
- Such plants can bear flowers and fruits earlier than those produced from seeds.
- Allows propagation of plants (banana, orange, etc) that have lost the capacity to produce seeds.
- All plants produced are genetically similar to the parent plant and hence have all its characteristics.
Question 36.
Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose.
(a) State the nature of the lens and reason for its use.
(b) Where should the palmist place/hold the lens so as to have a real and magnified image of an object?
(c) If the focal length of this lens is 10 cm and the lens is hold at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.
Answer:
(a) Nature of the lens will be convex lens to get a magnified image of the lines on the palm.
(b) It should be between F and 2F of the lens / or at F of the lens.
(c) Given, Focal length f = +10 cm and
Object distance u = -5 cm
Lens formula 1/v – 1/ u = 1/f
1/v – 1/-5 = 1/10
1/u + 1/5 = 1/10
1/v = 1/10 – 1/5 = 1-2/10
1/v = -1/10
v = -10 cm
M = himage/hobject
= v/u
= -10/-5
= 2
Therefore, the size of the image is 2 times the size of the object
OR
An object is placed at a distance of 60 cm 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).
Answer:
Distance of the image will be 20 cm in front of lens.
(b) Nature: Virtual
Position: 20 cm from lens on the same side as the object
Size: Diminished
Erect/Inverted: Erect
(c)
Section – E (12 Marks)
Question 37.
The melting points and boiling points of some ionic compounds are given below:
Compound | Melting Point(K) | Boiling Point (K) |
NaCl | 1074 | 1686 |
LiCl | 887 | 1600 |
CaCl2 | 1045 | 1900 |
CaO | 2850 | 3120 |
MgCl2 | 981 | 1685 |
These compounds are termed ionic because they are formed by the transfer of electrons from a metal to a nonmetal. The electron transfer in such compounds is controlled by the electronic configuration of the elements involved. Every element tends to attain a completely filled valence shell of its nearest noble gas or a stable octet.
(a) Show the electron transfer in the formation of magnesium chloride.
Answer:
Electron transferin the formation of magnesium chloride:
(b) List two properties of ionic compounds other than their high melting and boiling points.
Answer:
Two properties of ionic compounds are:
(i) They conduct electricity in a solution or molten state.
(ii) They are hard and brittle crystalline solids.
(c) While forming an ionic compound say sodium chloride how does the sodium atom attain its stable configuration?
Answer:
Sodium chloride is formed by the combination of sodium and chloride ions. Sodium loses one electron from the valence shell to attain a stable noble gas configuration.
OR
(c) Give reasons:
(i) Why do ionic compounds in the solid state not conduct electricity?
(ii) What happens at the cathode when electricity is passed through an aqueous solution of sodium chloride?
Answer:
(i) Ionic compounds do not conduct electricity in a solid state due to the absence of free ions but they conduct electricity in a molten and aqueous state
due to the presence of free ions.
(ii) Reduction takes place at cathode. Therefore, during electrolysis of an aqueous solution of sodium chloride, hydrogen gas is evolved at cathode due to the reduction of H+ ions.
2H+ + 2e– → H2 ↑
Question 38.
All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal copy and we have 22 such pairs. But one pair of sex chromosomes are odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes. But man has a mismatched pair in which one is normal sized while the other is a short one.
(a) In humans, how many chromosomes are present in a zygote and in each gamete?
(b) A few reptiles rely entirely on environmental cues for sex determinations. Comment.
(c) The sex of a child is a matter of chance and none of the parents is considered to be responsible for it. Justify it through a flow chart only.
Answer:
(a) Zygote is formed due to the fusion of male and female gametes. Gametes are haploid cells. Thus the fusion of two haploid cells results in the formation of a diploid cell. Therefore zygote is a diploid cell with 46 chromosomes.
(b) In a few reptiles, the temperature at which fertilised eggs are kept determines whether the animals developing in eggs will be male or female. By this, we can say that some animals rely entirely on environmental cues for sex determination.
(c) There is an equal chance of fusion of either X or Y chromosome with the egg. So, we can say that the sex of a new born child is a matter of chance and none of the parents is responsible for it.
OR
(c) Why do all the gametes formed in human females have an X chromosome?
Answer:
Human females are homomorphic. They have two sex chromosomes that are identical. One X-chromosome enters each gamete during meiosis at the time of gamete formation. So, all gametes have an X-chromosome.
Question 39.
The picture shows an electric circuit.
(a) Which of these is true about the circuit? Circle ‘Yes’ or ‘No’ for the correct response.
Is this true for the circuit | Yes or No |
The circuit is open. | Yes/No |
The circuit has double batteries. | Yes/No |
The circuit has an ammeter and a voltmeter parallel to each other. | Yes/No |
(b) Will there be any change in the ammeter reading if the length of the wire in the circuit is doubled? Explain your answer.
(c) How is ammeter connected in the circuit to measure electric current?
Answer:
(a)
Is this true for the circuit | Yes or No |
The circuit is open. | No |
The circuit has double batteries. | Yes |
The circuit has an ammeter and a voltmeter parallel to each other. | No |
(b) The ammeter’s reading will be decreased by one-half.
When the length of the wire is doubled, the resistance is also doubled, because resistance is directly proportional to the length of the wire. Hence according to Ohm’s law, for a given potential difference, the current reduces to half.
(c) Ammeter is connected in series in an electric circuit.
OR
(c) What is the shape of the graph obtained by plotting the potential difference applied across a conductor against the current flowing through it?
Answer:
A straight line is passing through the origin and has a constant slope.