CBSE ANNUAL PAPER - 2000

SCIENCE (THEORY)

(SET-I)

General Instructions :

(i) All questions are compulsory.

(ii) Marks for each question are indicated against it.

(iii) Question numbers 1 to 10 are very short answer type questions, carrying 1 mark each to be answered in one word or maximum in one sentence.

(iv) Question numbers 11 to 20 are short answer type questions. Carrying 2 marks. answer may not normally exceed 40 words each.

(v) Question numbers 21 to 30 are short answer type questions of 3 marks each. Answer may not normally exceed 60 words each.

(vi) Questions numbers 31 to 33 are long answer type questions, carrying 5 marks each, which should not be answered in more than 100 words each.

(vii) Please write down the serial number of the question before attempting it.

Mention two harmful effects of nuclear radiations on human body.

Name any two constellations that are visible during winter in the northern hemisphere.

How does nuclear fuel of a star differ from that of a white dwarf?

- a white dwarf is helium.

Which component of sunlight facilitates drying of whet after harvesting ?

A man found that he suffers from repeated sneezing when ever he exposed to dust. What could be the reason for such a reaction ?

Roughage is the cellulose of plant cells - undisgestable by our body, but it is helpful in digestion as it increases the bulk of food, maintains the movement of food through intestine and avoids constipation by moistening the walls of intestine.

Which of the following belonging to a food chain is likely to have maximum concentration of harmful chemicals in its body ?

Kingfisher, Zoophlankton, Fish, Phytoplankton.

Kingfisher - Would have a maximum concentration of harmful chemicals as it is at the top of the formed food chain.

An astronomer claimed to have discovered a pulsar in a distant galaxy. Mention any one observation that he might have made to claim his discovery.

Emission of radio waves from the centre of the circle in which circle any star is moving with no visible star in the centre.

Mention any four differences between an external combustion engine and a petrol engine.

Describe the process of obtaining coke from coal. Name the gaseous by - product obtained in this process.

Destructive distillation : Coke is obtained from coal by a simple process known as destructive distillation in which coal is heated in the absence of air.

Gaseous by - product - Coal gas.

How are antibiotics beneficial to us ? Name any two groups of organisms from which they are obtained.

Antibiotics - Antibiotics are used to treat the bacterial diseases viz. cholera, pneumonia, T.B. etc. Antibiotics destroy the bacteria responsible for disease without harming our body.

Name of group : Antibiotics are obtained from Fungi and Bacteria.

Why is conservation of wild life important ? Give any two reasons in support of your answer.

1.Wild life should be conserved to maintain the ecological balance in nature. Wild life is important link in food chain.

2. Wild life conservation is important as it preserve the gene pool. It helps to preserve the extinction of rare varieties of birds and animals.

Wild life can be conserved by adopting the following measure :

1. Hunting of wild animals should be banned.

2. National parks and sanctuaries should be established to provide natural habitat to the wild animals and birds.

Cleaning action of soaps : Soap molecule possesses two ends, one hydrocarbon end and the other - COONa end.

Hydrocarbon end is water repellant - (Hydrophobic) while the COONa end is bydrophillie ( water attracting). Soap solution in water form miscelles i.e. they arrange themselves radially such that hydrocarbon ends inward and COONa end towards out. Hydrocarbon end combines with dirt or grease particle and - COONa end combines with water molecules, when dirty cloth is wetted. During washing miscelles remove the dirt from the wet surface and is drained off with water flow.

List any four conditions that are essential for the life to originate and flourish on a planet.

The following conditions are needed for the origin and flourishment of life on a planet :

1. There should be present building ( body building) blocks like elements C,H,O,N,P etc. which may synthesise complex compounds necessary for body building.

2. Proper temperature range so that life sustaining chemical reactions may occur.

3. Presence of a liquid medium to transport nutrients like water.

4. Presence of protective blanket to protect the life from ultra violet rays from sunlight like ozone layer.

Heat produced on burning 5.0 g. or a fuel raises the temperature of 1.0 kg. of water from 20⁰ C 60⁰C . If the specific heat of water be 4.2J/g/⁰C. Calculate the calorific value of the fuel.

Mass of water = 1.0 kg. = 1000g.

Change in temperature = 60-20 = 40deg.C

Sp heat of water = 4.2J/g/⁰C

Heat gained by water r= Heat produced by fuel on burning.

He gained by water = m x s x t = 1000g x 4.2 x 40deg. J.

Calorific value of fuel = 1000 x 4.2 x 40 / 1000 x 5 = 33.6 KJ/g.

With the help of a diagram explain how the design of a box type solar cooker ensures minimum loss of heat from its inside.

A person decides to take only milk and nothing else in his diet for a year. Which one of the essential nutrient will not be available to him ? Mention any two symptoms of deficiency of this nutrient.

Symptoms .(i) Swelling and bleeding of fumes.

(ii) Loosening of teeth.

(iii) Pain in joints and general weakness.

Draw a diagram to show the orbit of an artificial satellite of the earth. Mark the position of apogee, perigee on it.

The following diagram is displaying the position of above orbit :

Describe sequentially the processes, that led to the formation of petroleum in nature, Name the aviation fuel used in aeroplane jet engines.

Formation of Petroleum - It is believed that petroleum is formed formed micro - organisms living in the sea.

(i) When these organisms die, they sink to the bottom and are gradually covered by sand and clay.

(ii) Over a period of millions of years, these remains are converted into hydrocarbons by heat, pressure and catalytic action in the absence of air.

(iii) These hydrocarbons as a mixture is petroleum which is found between impermeable rocks.

Aviation Fuel - A special Grade of Kerosene is used as aviation fuel in aeroplane Jet engines.

Describe the process of generation of energy in the sun. Name the scientist who was the first to propose this explanation.

The process by which energy is released in the Sun in Nuclear fusion of hydrogen atoms in the core of Sun. This process involves the combination of hydrogen nuclei into helium nuclei and releases a huge amount of energy. This fusion reaction started due to high temperature in the core, caused by the contraction of core under gravitational force of it.

Name of the Scientist : A German physicist, Hans Beete' proposed that the source of Sun energy is the nuclear fusion of hydrogen in its core.

What is transplantation ? What are its two advantages ? Name any two crops that are usually grown by this method.

Transplantation : Sees of some crops are grown in a small part of field ( nursery). After some growth the seedlings are transplanted in a prepared field at proper distance. Later on these seedlings grow and develop there.

This process is know as transplantation.

Advantage : 1. Better and healthy seedling are selected for cultivation by this process.

2. Crops grow and develop rapidly.

3. Proper distance can be maintained between crop plants for their better growth.

4. Weeds are left behind in the nursery.

5. Roots penetrate the soil better.

Name of crops : (i) Paddy

(ii) Chilly

(iii) Brinjal, tomato, onion.

What is ten percent law ? Explain with an example how energy flows through different trophic levels ?

Ten percent law - Flow of energy, in a food chain takes place by a law known as 10 % from one trophic level to the next trophic level.

According to 10 % law only 10 % of the energy entering a particular trophic level is available for transfer to the next higher trophic level as 90 % of that is utilised by the organism of that trophic level. In simple term it is called as 10 % law.

With the help of a labelled diagram describe the method of preparation of methane in the laboratory. Is this gas combustible ? How can you test this property ?

Preparation of Methane : Methane is pre pared in the laboratory by heating sodium acetate and soda lime.

Test for combustibility - Fill up a boiling tube with methane and bring a burning splinter in the boiling tube containing methane gas. Methane gas burns with a bluish flame.

The mass of a star is 10 times that of the sun. Describe last two stages in the life cycle.

When a star has its initial mass much more than that of the sun then it gets the following final stages in its life after the end of red giant phase.

(i) Supernova : The core of helium formed during the red giant phase would continue to contract due to its own gravitation building up higher and higher temperatures. As this contraction continues the energy liberated causes the outer envelope to explode with a brilliant flash and it could release the same amount of energy in one second as the sun radiates in about a hundred years. Such exploding star is called supernova.

This supernova explosion liberates clouds of gases which would contribute to the raw material for the formation of new star.

(ii) Neutron Star : After supernova explosion only core of star survives and continue to contract resulting to a extremely dense lump known as neutron star. Densities of neutron star may be about million tonnes per cubic centimeter.

(iii) Pular : a spinning neutron star emits radiowaves and called pular.

Describe any three ways in which biotic and biotic environment may cause variation in the size of population of deers in a forest.

Following environment factors can cause variation in the size of deers' population in a forest.

(i) Nutrients supply : Supply of sufficient grass by the forest will increase the size of deers population while non-availability of nutrients ( grass) will decrease it.

(ii) Available space : Sufficient availability of space or forest favourable which provides safe and flourishing environment, will increase the size of population while the adverse will decrease.

(iii) Interaction with other organism : Dense population of predators ( like lion) will decrease the population of dears in a forest by eating them while the reverse will increase.

With the help of a labelled diagram describe the process of extraction of sulphur by Frasch process.

Extraction of Sulphur : Sulphur is found in free state at the depth of about 1000 feets in the soil. It is extracted by the process 'Frasch Process'. A hole is bored to the sulphur beds and three co-centric pipes an pushed to the beds of sulphur. Since the melting point of sulphur is (112.8 deg c) low and it is insoluble in water, super heated water is forced down through the outer most pipe. The heat of water get it be melted. Now hot compressed air is blown through the inner most pipe. By the presence of compressed air molten sulphur comes out at the surface of earth through middle pipe in the form of froth ( Foams).

The efficiency of a petrol engine is 30 %. Calculate the power delivered by it if it burns 0.03 kg. or petrol in one minute. The calorific value of petrol is 50 KJ/g.

Mass of petrol burnt = 0.03 kg. = 30 g.

An element belonging to group V of the Periodic Table is available in nature in two forms, A and B. The ignition temperature of A and B are 260 deg c and 30 deg. c respectively. Identify the element. Name its two forms. Name (i) the form that reacts with concentrated solution of sodium hydroxide and (ii) the one that would react with chlorine with heating. Write the equations for the reactions involved.

Form - form A is Red Phosphorus.

Form B is yellow or white phosphorus.

Reactions : - (i) Yellow Phosphorus reacts with cone. Solution of sodium hydroxide.

State the factors that help to determine that wheat crop has matured for harvesting. Describe how biotic and abiotic factors may affect the quality of stored grain. Mention any two effects of each type of factors.

Factors which determine the maturity of wheat crop for harvesting.

1. The crop should have absorbed all the necessary nutrients from the mother plant.

2. The whole plant should become some hard, dry and golden in colour.

3. The moisture content of the grain should not be more than 14 % at the time of harvesting to ensure safe storage. It can be estimated by crushing some wheat grains between the teeth, if it cracks, the moisture content is just right for harvesting.

Biotic factors - 1. Microbes - On being moisture content more than 14 % of stored grain, infestation of microbes - Bacteria and fungi, damage the stored grains. The action of microbes may result in loss of weight, decoloration, heating, introduction of toxins and failure to germinate.

What is a nuclear reactor ? Explain how nuclear fission reaction is controlled in a reactor ? Mention any two advantages and any two disadvantages of harnessing nuclear energy.

Nuclear reactor - It is a device in which energy from controlled nuclear fission reaction is obtained for useful purposes.

Controlled chain reaction - When slow moving neutron collides with the nucleus of U-235, it make the nucleus of U-235 unstable and breaks into two smaller nuclii of 94/36 Kr and 139/56 Ba. During this fission of nucleus a huge amount of energy is released and three neutrons set free which further break three more nuclei of U-235 with a production of three times more energy than the previous fission. Thus set free three times neutrons in every fission break three times more U-235 nuclii. A reaction occurs in the form of chain known as chain reaction. In very shores time a very very large amount of energy liberates in an uncontrolled form.

To control the amount of energy liberated, out of three neutrons, set free during fission of U-235 nucleus, some are absorbed by using neutron absorbant such as cadmium, boron, graphite etc. the number of fissions of U-235 nuclei are so made by absorbing excess neutrinos that the energy liberated remains controlled is called controlled chain reaction.

Advantage - 1. It is a long lasting rich and concentrated source of energy.

2. If some moderate precautions are taken, it does not pollute air like other resources' use viz. use of coal, oil, wood etc.

Disadvantage - 1. There is an additional danger of harmful wastes produced at various steps of nuclear cycle which includes mining, enrichment of ore and of course the nuclear reaction inside the reactor. They emit nuclear radiations which cause irrespective damage to livings.

2. Always is a threat of accident in reactor which releases harmful radiations - B and Y ( gamma) rays.

State the three main steps involved in metallurgical processes. Explain the method of extraction of copper from its sulphide ore. Write the chemical reactions involved.

Metallurgical processes - Following steps are involved in metallurgy.