CBSE ANNUAL PAPER - 1998

SCIENCE (THEORY)

(SET-I)

Time Allowed : 3 Hours

Maximum Marks : 75

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.

Name the device which directly converts solar energy into electrical energy.

Name the technique of collecting information through a satellite about an object from a distance.

An engine supplies 12,000 joule of energy per minute. How much power is supplied by it ?

Time - 1 min. = 60 sec.

Power = Energy / Time

= 12,000/60 = 200 watt.

Lights from two different sources A and B have wave lengths 0.3 micron and 0.7 micron respectively. Which one of the two lights carries more energy per photon ?

Light from source A carries more energy per photon as its wave Length is smaller.

Name any two gases whose presence in air causes green-house effect.

Diamond is transparent with high refractive Index and it possesses excellent cleavage along many intersecting planes which can be polished. All these three properties make it special shining substance.

The micro-organisms responsible for the spoilage of milk are destroyed on boiling, hence it does not spoil quickly.

Which one of the following in a food chain will have maximum concentration of harmful chemicals in its body :

Small fish, Zooplankton, Birds, Phytoplankton.

Phytoplankton -- Zooplankton -- Small fish Birds.

As birds are at the top of the food chain, so, birds will have the maximum concentration of the harmful chemical in their body.

A farmer grows rice crop year after year in his field. He notices a gradual decrease in yield. What could be its cause ?

Gradual decrease in yield is noticed by farmer due to depletion of nutrients, particularly nitrogen, in the field caused by monoculture i.e. growing the same crop (rice) in the same field year after year. Field becomes depleted of certain nutrients which decreases yield.

Name the full gases formed when (i) steamand (ii) a restricted amount of air are passed through a bed of red hot coke. Write the names of their combustible components :

C + H₂O --------- CO + H₂

Red Hot Steam Water gas

Coke

Both the components of water gas i.e. CO and H₂ are combustible.

(ii) When restricted amount of air is passed over red hot coke, producer gas is produced which is a mixture of CO and N₂ gases.

C + AIR ---------- CO + H₂

Red Hot Restricted amount Producer gas

Coke

CO, carbon monoxide of producer gas is the combustible component.

Calculate the power of an engine which can lift 300 Kg. of water through a vertical height of 15 m in 15 seconds. ( g = m/s² ).

Height (h) = 15 m.

Acceleration due to gravity (g) = 10m/s².

Energy required or work done by engine = m x g x h.

= 300 x 10 x 15 J

= 45000 J

Power = work done / time

Power of engine = 45000/15 = 3000 watt. ( 3 K. watt.)

Mention any two differences between chemical and nuclear reactions.

(i) Electrons of outer most orbit take part in a chemical reaction while the nuclear particles - protons and neutrons remain unaffected.

(i) Nuclear particles - protons and neutrons take part in a nuclear - reactions while the electrons remain unaffected.

(ii) Amount of energy produced or absorbed in a chemical reaction s is very very low as compared to nuclear reaction.

(ii) Energy produced or absorbed in a nuclear reactions is very high as compared to chemical reaction.

Kerosene burns in a cooking stove to give a blue flame while it gives a yellow flame when burnt in a lantern. Give reasons for this difference.

(i) Kerosene is burnt in a cooking - wick stove or pressure stone with sufficient amount of air, so it burns with a blue flame due to its complete combustion. Wick stove possesses a perforated sheet around the wicks. These perforations allow the hot air to enter near the wicks to aid in combustion while in a pressure stove Kerosene coming out from the burner strikes with hot burner and converts into vapours. These vapours get sufficient air from surrounding and complete combusion occurs with a blue flame.

(ii) In a lantern, there is no provision for the free supply of adequate oxygen ( or air ) for the complete combustion of Kerosene in wick of lantern. Thus Kerosene in a lantern burns in insufficient oxygen ( or air ) which leads to incomplete combustion and unburnt particles rise in flame. These particles glow in hot flame and make the flame luminous in yellow colour.

1. It is a heavenly body having its own light which make it illuminated.

1. These are the heavenly bodies from sky which are reflected from their path and are attracted towards earth when they enter the atmosphere, start to burn due to friction of air.

2. Their mass is very much higher than a shooting star and made up of mainly hydrogen and helium gases.

2. Their mass is very less comparatively and are made up of dust and solid bodies.

Smog : Smog is a mixture of smoke and fog. During winter when smoke from industries, vehicles or houses, mixes with the condensed water vapours and dust particles, smog is formed. Generally it is found in industrial areas, big cities or over - crowded area. It is the major problem of metropolitan areas. Smog contains some harmful fumes also. Smog does not go high into the atmosphere as a layer of warm air is formed over the smog and cover it.

Name of diseases : Smog causes bronchitis, Heart diseases, lung cancer and some other respiratory diseases.

A trivalent metal X is manufactured by the process of electrolysis. It is the most abundant metal in the earth's crust. Identify the metal and state its two uses.

X metal is trivalent, manufactured by electrolysis and is abundant in earth crust; so , it is Aluminum.

Uses : (i) Aluminium is used to make the electric wires for conduction of electricity as it is good conductor of electricity.

(ii) Door frames, windows, handles, utensils and aircraft frames, engine parts are made from aluminium.

What is meant by a functional group in an organic compound ? Give the structural formulae of the functional groups in (i) Acetic acid and (ii) ethyl alcohol.

Functional Group : A group of elements in organic compounds when replaces hydrogen atom of hydrocarbon, produces specific properties in the compound and is known as functional group. e.g. OH naming hydroxyl group produces alcoholic properties while - COOH naming carboxyl group produces acidic properties in the organic compounds.

(i) In Acetic acid ( CH₃ COOH ) - cooh, Carboxyl group is the functional group.

O

Structural formula : - C - OH

(ii) In Ethyl alcohol, OH, hydroxyl group is the functional group.

Structural formula - OH.

Sickle Cell anaemia : Sickle cell anaemia is a genetic disease which is transferred generation to generation. It is caused by mutant gene. In this disease RBC of the affected person become sickle shaped instead of round and haemoglobin becomes defective.

Effects : Because of defective haemoglobin, patient becomes deficient of oxygen and following effects are seen :

(i) Headache and dizzliness.

(ii) Cardiac and pulmonary changes.

(iii) Nausea and even death.

Mention the difference between the food habits of organisms belonging to the first and third trophic levels. Give one example of each of them.

First trophic level : Organisms at first tropic level are the producers which contain chlorophyll and are capable to manufacture their organic food from in organic substances - CO₂ and H₂O in the presence of sunlight e.g. Green lands.

Third trophic level : Organisms at third trophic level are the carnivores which are not capable to manufacture their food like that of green plants rather they get their food from the herbivores in the form of flesh.

Describe the construction of a solar cooker. How does it cause a rise in temperature to cook food ?

Construction of a solar cooker : (Box type ) : It consists a blackened insulated box of wood or of a similar material. Its upper open part is covered with a glass sheet. The inner walls of the box are painted black to maximum absorption of heat and to minimise heat losses due to reflection. Glass sheet allows to enter the considerable visible light and infra-red rays from sunlight into the box but do not allow to go out the radiated heat from inner blackened walls and thus inner part of the box gets sufficient temperature for cooking the food.

Inner part of lid of the box is made good reflector and lid is so attached with the box that it can be adjusted at different angles to reflect the maximum sunlight on the inner blackened walls of the box. Cooking pots with food stuffs are placed in the box.

Rise in temperature : When a solar cooker is placed in sunlight in such a way that the sunlight falling on reflector enters the blackened box through glass sheet. Its inner surfaces become hot after absorbing solar energy. As a result, these surfaces start radiating heat in the form of infra red rays. Glass sheet does not allow these rays to go out as the wave length of these infra - red rays is relatively longer. Thus temperature of the inner part of the box rises upto 100⁰ - 140⁰ C which is sufficient to cook the rice, pulses, meat etc.

What are rocket propellants ? Mention any two of their important characteristics. Give an example of liquid propellants.

Rocket Propellant : Special fuels that are highly compact and burn rapidly and completely producing a very large volume of gases per gram weight leaving no dead weight of residue, are called rocket propellants.

Characteristics : (i) They must burn rapidly and completely.

(ii) They should produce a large volume of gases per gram weight.

(iii) They should not leave dead weight residue.

(iv) They should be compact.

Liquid Propellant : Liquid hydrogen with liquid oxygen.

Name the process involved in the liberation of energy in (i) the sun and (ii) a nuclear reactor. Mention any two differences between the two processes.

In Sun : Energy is liberated by nuclear fusion process in the sun.

In Nuclear Reactor : Nuclear fission is the process by which energy is liberated in the nuclear reactor.

Differences :

(i) Smaller nuclei fuse to form a big nucleus in this process. e.g. Four hydrogen atoms fuse to form the nucleus of helium.

H H

+ -------------- He

H H

(i) A bigger nucleus splits up into two smaller nuclei in this process. e.g. U-235 nuclear splits up into Kr. and Banuclei when slow moving neutron is bombarded on U-235 nucleus.

(ii) This process can not be performed in the laboratory as it required very high temperature to start.

(ii) It can be performed in the laboratory and can be controlled.

The mass of star A is 1/10th of the mass of star B. The mass of star A is nearly equal to the mass of the sun, so the mass of star B is about ten times more than that of sun. Therefore, star B will end up as supernova.

The other star A having the mass equal to the mass of the sun will end up as a white dwarf star. After the end of red grant phase. Its outer shell. The core left behind would gradually condense into an extremely dense ball of matter. The resulting in full temperature in its interior would then begin the helium to fuse into higher elements like carbon in the same way as the hydrogen was fused into helium. The energy liberated by its core make this core glow and a white dwarf star as long as the helium lasts before ending into a dense lump.

Define Isomerism. Write the structural formulae and the names of the isomers of butane.

Isomerism : The property of compounds by virtue of which compounds have the similar molecular formula but different structural formula, is known as isomerism.

Isomers of butane :

H H H H H H H

| | | | | | |

H -- --C----C----C------C---H-----H--C------C---------C-----H

| | | | | | |

H H H H H | H
| | |

normal - Butane H------C----------H

n - butane |

(C₄H_{10) H}

Iso - Butane

(C₄H₁₀₎

Describe any three ways in which the water important for the activities of living beings.

(i) As solvent : Many substance are required by the livings in the solution form where water acts as solvent viz. digested food is absorbed by the body in the solution farm.

(ii) As carrier : Water carries waste products in the body to the excretory organs from where they are excreted out from the body.

(iii) Regulates body temperature : Water in the form of sweat evaporates and thus regulates the body temperature during summer.

A cow is being fed on straw, oil cake, oil-seeds, gram and bajra. To what classes of feed to these items belong and what is their importance ?

(i) Straw belongs to the Roughage class of feed which provides cellulose i.e. carbohydrate to the body. It provides energy and raw material for the formation of fats in the animal's body.

(ii) Oil cake, oil seeds, gram and bajra belong to the concentrate class of cattle feed.

They provide proteins, vitamins and minerals to the animal. It is energetic, it provides body building material and regulates metabolic activities in the body.

Moisture content of four food items P, Q, R and S is 10 %, 15 %, 25 % and 50 % respectively. Which of these require cold storage and which ones dry storage ? Give reasons.

Cold Storage : Food items R and S containing 25 % and 50 % moisture respectively should be stored at low temperature i.e. these two require cold storage as they have higher moisture content than safe limit Higher moisture can facilitate the micro-organisms to grow and they spoil the food. At low temperature the growth of microbes reduced and their action is inhibited. Low temperature inhibits the enzymatic action also.

(i) Enzymes become inactive.

(ii) Growth of microbes is reduced.

(iii) Microbes become inactive.

(iv) Infestation of insects is also inhibited.

Dry storage : Food items P and Q having low moisture i.e. 10 % and 15 % respectively, can be stored at room temperature. Food items having 14 % moisture, remain safe at room temperature as this moisture content does not facilitate the microbes insects and enzymes to be active and food does not spoil.

Name the radiation's absorbed by the ozone layer. Give any two causes of the depletion of ozone layer. Name the disease likely to be caused due to its depletion.

Ozone layer absorbs the ultra violet Radiations coming from the sun.

Causes of ozone depletion : (i) Excessive use of 'Aerosol' chemicals like chlorochloro carbon ( clcIC), chlorofloro carbon (cl.F.C.) destroy the ozone layer.

(ii) Gases released from the Rocket -exhaust also dissolve the ozone layer and deplete it.

Disease : Depletion of ozone will allow the ultra violet rays to reach the earth surface where they will cause :
(i) Skin cancer

(ii) Damage to the new cells

(iii) Gene mutation resulting in genetic diseases in livings.

What is nitrogen fixation ? Mention two points of difference between nitrification and denitrification processes. Name the organisms involved in these processes.

Nitrogen fixation : Green plants cannot utilise the free atmospheric nitrogen for their growth and food manufacturing. Some bacteria like Rhizobium and some blue green algae are capable to convert the free atmospheric nitrogen into nitrate form, which can be readily utilized by plants. This process of conversion of free atmospheric nitrogen to nitrates is known as nitrogen fixation.

(i) The fixed nitrogen is amonified by microbes i.e. it is converted to ammonia. This ammonia is converted by some other microbes into nitrite and nitrates, it is know as nitrification.

(ii) It is oxidising process.

Organisms :

* Ammonia to nitrite - Nitrifying bacteria

( Nitrosomonas)

* Nitrite to Nitrate - Nitrobactor

(i) By other kind of microbes nitrates are converted to free nitrogen, it is known as denir-ification.

(ii) It is of reduction type process.

Organisms :

Nitrate to Nitrogen - Pseudomonas ( Denitrificating bacteria)

Draw diagram of a nuclear reactor. What is the role of moderators in it? How are nuclear reactor used to generate electricity ?

Use of nuclear reactor to generate electricity : As nuclear reactor is fired the nuclear fission reaction starts. Heat generated in the reactor is withdrawn by circulating liquid sodium continuously through pipes embodied in the reactor. Liquid sodium becomes hot on gaining heat from the reactor and gives to the water of heat(-) exchanger when it passes through coiled pipes embedded into the water of heat exchanger. This heat generates steam. Super heated high pressure steam is passed through turbine chamber with the help of pumps. It drives the turbine. Turbine rotates the generator by virtue of which electricity is generated. The used steam condenses and passed through a condenser to heat exchanger back in the form of water for the formation of new steam.

Here generation of electricity is shown in the following diagram.

(i) Describe the steps involved in manufacture of blister copper from concentrated copper sulphide ore.

(ii) State the process of obtaining pure copper from blister copper with the help of a labelled diagram.

(iii) Name the elements which are mixed with copper to prepare German silver.

Following steps are involved in the manufacture of blister copper from concentrated copper sulphide ore :

(i) Roasting : Concentrated ore is roasted in the presence of air on a furnace i.e. strongly heated inthe adequate quantity of air. In roasting a part of CUS ( concentrated ore) is converted into copper oxide (CuO) and other volatile impurities which escape away in the form of gases.

D

2CuS + 3O₂ ------ 2 CuO + 2SO₂

(ii) Reduction : After roasting CuO is reduced to Cu either by using a reducing agent viz. Coke or reduced by stopping air supply during roasting following reactions occur.

D

2CuO + CuS ------ 3 Cu + SO₂

D

2CuO + C ------ 2 Cu + CO₂

(iii) Blister Copper : Copper thus formed is in molten state. Since sulphur dioxide gas passes though molten copper, sort of blisters are developed on the surface of copper. Similar situation arises during escape of CO₂ through molten copper. The pure copper is obtained by electrorefining of blister copper.

(iv) Refining of blister copper : Blister copper is refined by the electrolysis process. A pure copper wire is made cathode and the rod of impure blister copper is made anode. CuSO4 solution is taken as electrolyte in a electrolytic cell. On passing electricity pure copper is obtained deposited at cathode while the impurities remain near anode. Timely, impure blister copper rod is again inserted at anode to get it be purified.

At Anode : Cu - 2e = Cu⁺⁺

At Cathode : Cu⁺⁺ + 2e = Cu

(iii) German silver : German silver is an alloy of Cu, Ni and Zn. Thus nickle and zinc are mixed with copper to obtain German silver.

(ii) What are end products of protein digestion and where are they absorbed ?

(iii) Name any three types of proteins found in our body and mention their functions.

(i) C,H,O and N are the main elements which constitute the proteins. Besides these elements S and P are also found in some of the proteins.

Proteins are digested by the action of proteinase enzymes into amino acids. The digestion of proteins occurs into stomach and small intestine while the digested proteins i.e. amino acids are absorbed by the small intestine.

(iii) There are many types of proteins. Each type perform specific functions like -

(a) Transport protein e.g. Haemoglobin. Transport proteins transport some substances from one part to the another part of the body. Haemoglobin carries O₂ from lungs to each and every part of the body and carries CO₂ back to the lungs from where it is exhaled out from the body.

(b) Enzyme e.g. lipase. Enzymes are the catalysts found in living cells which catalyse specific chemical reactions in the body at body temperature. for lipase catalyses the digestion of fats into fatty acids.

(c) Protective Proteins e.g. Antibodies. Antibodies are such proteins which protect the body from diseases, thus immune the body.