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- Q) here is cbse 2007 question paper of science: cbse xscience and technology (theory) 2007(outside delhi) time allowed: 2 hours 15 mins; maximum marks: 100 general instructions: 1) the question paper comprises of two sections a and b. you are to attempt both sections. 2) you are advised to attempt all the questions of section a and section b separately. 3) all questions are compulsory. 4) there is no overall choice. however, internal choice has been provided in some questions. you are to attempt only one option in such questions. 5) marks allocated to every question are indicated against it. 6) questions number1-4in section a and17, 18in section b are very short answer questions. these are to be answered inone wordorone sentence. 7) questions number5-8in section a and19, 20in section b are short answer questions. these are to be answered in30 - 40words each. 8) questions number9-14in section a and21 -23 in section b are also short answer questions.these are to be answered in40 - 50words each. 9) questions number15, 16in section a and24in section b are long answer questions. these are to be answered in70words each. section a question 1 1. what is the role of a catalyst in a chemical reaction? solution: a catalyst alters the rate of reaction without itself undergoing any change. question 2 2. which class of compounds gives a positive fehling’s test ? solution: (out of syllabus) question 3 3. approximately how many stars are there in the milky way ? solution: (out of syllabus) question 4 4. what is meant by the statement, “potential difference between points a and b in an electric field is 1 volt.”? solution: potential difference between points a and b in an electric field is said to be one volt when one joule of work is done in bringing a charge of 1 coulomb from point a to point b. question 5 5. state the ‘law of chemical equilibrium’. write an expression for the equilibrium constant (k) for the reaction, solution: (out of syllabus) question 6 6. name the organic acid present in vinegar. write a chemical equation which represents the commercial method for the preparation of this acid from ethanol. solution: the organic acid present in vinegar is acetic acid,.acetic acid is be prepared by oxidizing ethanol. question 7 7. distinguish between ‘artificial’ and ‘natural’ satellites. why artificial satellites are called “eyes in the sky” ? solution: ana rtificial satellite is a man made object that continuously orbits earth or some other body in space. a natural body which revolves around a planet is called natural satellite. moon is a natural satellite of earth. they are used to study the universe, help forecast the weather, assist in the navigation of ships and aircraft and support military activities hence known as “eyes in the sky”. question 8 8. an electric lamp is marked 100 w, 220 v. it is used for 5 hours daily. calculate (i) its resistance while glowing. (ii) energy consumed in kwh per day. solution: given, p = 100 w, v = 220 v, t = 5 hours, r =? and e =? by definition, substituting the values, we get, r = 484 ohms therefore, the resistance while glowing is 484 ohms. the energy consumed can be determined as, substituting the values, we get, therefore, energy consumed in kwh per day is e = 0.5 kwh. question 9 9. (a) write the chemical name and formula of bleaching powder. (b) why does bleaching powder smell of chlorine when exposed to air? (c) write chemical equation to represent the action of dilute hydrochloric acid on bleaching powder. solution: a) the chemical name of bleaching powder is calcium oxy-chloride and the formula is b)bleaching powder smells of chlorine when exposed to air since, it reacts with carbon dioxide of air and liberates chlorine. c) bleaching powder reacts with hydrochloric acid, and forms calcium chloride, water and chlorine gas. question 10 10. what is meant by ‘dehydrating agent’? describe with a chemical equation, an activity to show that concentrated sulphuric acid is a strong dehydrating agent. solution: a substance that removes water from a compound is called dehydrating agent. in the preparation of ethene from ethyl alcohol sulphuric acid is used as a dehydrating agent. question 11 11. give reasons for the following : (i) oxidation of ethanol with cro3 produces ethanal while ethanol when oxidised with alkaline kmno4 produces ethanoic acid. (out of syllabus) (ii) propanone forms addition product with hcn.(out of syllabus) (iii) alcohol supplied for industrial purposes is mixed with copper sulphate. solution: iii) copper sulphate imparts blue colour to alcohol, hence, it becomes easier to identify alcohol meant for industrial purpose. to prevent misuse of industrial alcohol, it is denatured with methanol and copper sulphate. methanol makes it poisonous, and copper sulphate imparts blue colour. question 12 12. an object 50 cm tall is placed on the principal axis of a convex lens. its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. calculate the focal length of the lens. solution: given, ho= 50 cm, hi= -20 cm,= 10 cm, according to the formula, = -25 cmaccording to the formula, = 7.143cm therefore, the focal length of the lens is 7.143 cm. question 13 13. (a) state one limitation of solar energy available from solar cells. (b) what is the minimum wind velocity required to obtain useful energy with a windmill? (c) define the term ‘nuclear fission’. solution: a device which converts solar radiations directly into electrical energy is called a solar cell. a. we cannot operate a solar cell during night which is a limitation of solar energy available from solar cells. b. wind energy farms can be established only where the minimum velocity of wind is 15 kmph. this velocity is not available everywhere. c. when an unstable nucleusis bombarded with a slow moving neutron, it splits up into two medium size nuclei, release some neutrons and an enormous amount of energy. this process is called nuclear fission. question 14 14.(a) state ohm’s law. (b) draw a schematic diagram of the circuit for studying ohm’s law. solution: a. according to ohm’s law, the current flowing through a conductor is directly proportional to the potential difference applied across the ends of the conductor, provided the physical condition remains the same. mathematically, where, r is the proportionality constant known as resistance of the conductor the si unit of resistance is ohm. a. a battery is connected to a fixed resistance r with a rheostat and a key k.ammeter a measures the current in the circuit and potential difference across the resistor is measured by the voltmeter v. at a particular setting of rheostat, we note the reading of ammeter and voltmeter. the total resistance in the circuit changes due to which the readings of ammeter and voltmeter also change. diagram: question 15 15(a) name the chief ore of iron. write its formula. (b)how is an iron ore concentrated? describe it briefly. (out of syllabus) (c)draw a labeled diagram of the blast furnace used in the extraction of iron from its concentrated ore. or (a) draw a labeled diagram of ‘frasch process’ used for extracting sulphur. (b) state the principle involved in the extraction of sulphur directly out of the ground. solution: (out of syllabus) question 16 16. a 14-year old student is not able to see clearly the questions written on the blackboard placed at a distance of 5 m from him. (a) name the defect of vision he is suffering from. (b) with the help of labeled ray diagrams show how this defect can be corrected. (c) name the type of lens used to correct this defect. solution: a. myopia or shortsighted means having good near vision but poor distance vision. as the student is not able to see clearly the questions written on the black board placed at a distance of 5 m from him he is suffering from myopia. b. b. this defect is corrected by placing a concave lens before the eye. the parallel rays coming from distant object is first diverged by the concave lens and then converged by the eye-lens. or (a) what is an electromagnet? (b) list any of its two uses. (c) draw a labeled diagram to show how an electromagnet is made. (d) what is the purpose of the soft iron core used in making an electromagnet? a. electromagnet is just a solenoid with a wire wounded on a soft iron core. it is a temporary magnet, it produces strong magnetic field only for the time current is passed through it. b. uses of electromagnets: i. for electrical devices such as electric trains. ii. for moving big objects of iron from one place to another. iii.for removing small iron splinter from an eye of a patient. c. diagram: d. e. an electromagnet can be made by winding an insulated copper wire on a soft iron core. when current is passed in the wire of electromagnet, the soft iron core converts into a magnet. the magnetic field of soft iron adds up with the magnetic field of solenoid and hence, an electromagnet produces stronger magnetic field as compared to a solenoid. the magnetic field of an electromagnet depends upon the magnitude of current and the number of turns per unit length. section b question 17 17. name the excretory unit of a kidney. solution: nephron is the excretory unit of a kidney. question 18 18. what are phytohormones? solution: phytohormones is a chemical substance that is produced naturally in plants such as auxins, gibberellins, abscisic acid and are capable of translocation and regulating one or more physiological processes when present in low concentration. question 19 19.point out two differences between an artery and a vein. or what is ‘osmoregulation ’? how does it take place in humans? solution: artery vein (1) most arteries are located deep in the body. (1) veins are situated superficially. (2) they contain oxygenated blood except pulmonary artery. (2) they contain deoxygenated blood except pulmonary vein. (3) they carry blood away from heart to various organs and tissues. (3) they bring blood from various organs and tissues into the heart. (4) their wall is thick, strong and less distensible. (4) their wall is thin, weak and more distensible. or osmoregulation is the process of maintaining the required amount of water and ionic balance in the body. osmoregulation takes place in kidney in humans. kidneys play a major role in osmoregulation, that is regulating the amount of water in urine waste .it is regulated by antidiuretic hormone (adh). adh stimulates nephrons to reabsorb water. question 20 20. explain ‘reflex action’ with a suitable example. solution: reflex action is defined as an unconscious, automatic and involuntary response of effectors, i.e., muscles and glands, to a stimulus, which is monitored through the spinal cord. for example, the iris of the eye can contract or dilate the pupil in response to changing light intensity without being aware that it is happening. question 21 21. explain double fertilization in plants. solution: double fertilization in plants: pollination is followed by fertilization in plants. after the pollen lands on a suitable stigma, it has to reach the female germ cell in the ovary. the pollen tube grows out of the pollen grain through the style to reach the ovary. after fertilization, the zygote divides several times to form an embryo within the ovule. the ovule then develops a tough coat and gets converted into a seed. the seed contains the future embryo which develops into seedling. the ovary develops and ripens to form a fruit. the process of double fertilization occurs inside each embryo sac, in which two fusion, syngamy and triple fusion take place. when one male gamete fuses with the egg contained in the embryo sac of the ovule, this fusion of male and female gametes is called syngamy and its product is the zygote. the other male gamete fuses with two polar nuclei and this process is called triple fusion, where three nuclei are involved in the fusion process, one male gamete and two polar nuclei. question 22 22.(a) what is a gene? (b)where are genes located? (c) what is the nature of gene? or define ‘evolution’. describe darwin’s theory of evolution. solution: (a) gene is the unit of inheritance in living organisms. (b)genes are located on the chromosomes and controls the appearance of a set of hereditary characteristics. (c)gene is made up of deoxy ribonucleic acid (dna).it is hereditary in nature, i.e. it transfers the characters from one generation to another. or evolution is the sequence of gradual changes that take place in the primitive organisms over millions of years and new species are produced. since the evolution is of the living organisms, so it is called “organic evolution”. darwin’s theory of evolution: charles robert darwin gave the theory of evolution in his famous book ’the origin of species’ the theory of evolution proposed by darwin is known as ‘the theory of natural selection’. it is also called ‘darwinism’. according to darwin’s theory of evolution: 1) there is natural variation within any population and some individuals have more favorable variations than others. 2) population remains fairly constant even though all species produce a large number of offspring. 3) this is due to ‘competition’ or ‘struggle for existence’ between same and different species. 4) the struggle for survival within population eliminates the unfit individuals and those with ‘favorable variations’ survive and pass on these variations to their progeny to continue. this is called natural selection. 5) the favorable variations are accumulated over a long time period leading to the origin of a new species. question 23 23. what is ‘soil erosion’? mention it’s any two effects. suggest two ways by which soil erosion can be checked. solution: soil erosion is the washing away of the topmost layer of soil. the effects of soil erosion are i) soil quality, structure, stability and texture can be affected by the loss of soil. textural changes can in turn affect the water-holding capacity of the soil. ii) surface runoff, causing gull formation or the enlarging of existing gullies. iii) pesticides may also be carried off the site with the eroded soil. soil erosion can be checked by afforestation, leavingcrop residueon the field after harvesting and by crop rotation. question 24 24.(a) draw a diagram of human ‘alimentary canal’. (b) label the following on the diagram drawn: oesophagus, liver, gall bladder, duodenum (c) what is the function of liver in the human body? solution: (c) liver serves both as a digestive as well as an excretory organ in the human body. the bile juice secreted by the liver make the chyme (the semisolid and partly digested food) alkaline for the action of enzyme secreted by pancreas and small intestine. bile from liver emulsifies the fats for their digestion and easily absorption