CBSE Set Qa2 Science Class X 1997 Sample Test Papers For Class 10th for students online

Science Class X (CBSE)
You are on answer 21 to 33

Q.21 If 768 kJ of energy is produced per hour in a nuclear fission reactor, work out the number of fissions that would be taking place in it in 10 minutes, given that the energy released per fission is 3.2 x 10¹¹J.

Ans21. Energy produced in 60 minutes = 768 kJ = 768000 J
Energy released per fission = 3.2x10^-11J
No of fissions occuring in 1 hour
     energy produced in the reactor

     energy released per fission
   768000J

   3.2x10^-11
= 24 x 10¹⁵
No of fissions taking place in 10 minutes (10/60 hr)
  24 x 10⁵ x 10

        60
= 4 x 10¹⁵

Ans. 4x10¹⁵ fissions per minute

Q.22 What is meant by the term "differentiation" ? Describe the major layers of earth with a labelled diagram.
Ans22. Differentiation is the phenomenon of reorganisation of primitive earth into layers of different densities under the influence of gravity.
On account of differentiation, the earth is divided into three layers:
(i) crust
(ii) mantle
(iii) core

Crust: It is the outermost layer of earth. It is made up of light rocks rich in silica and aluminium and has a low density. The three-quarters of the earth's crust is convered with water.
Mantle: The mantle is in between the crust and core. It consists of rocks which are made up largely of iron silicate and magnesium silicate.
Core: It is the innermost part of the earth. It is mainly made up of iron and some nickle. The core of the earth consists of two parts:
(i) inner core
(ii) outer core
The temperature at the centre is about 4000°C and the pressure is about 3.7 times the atmospheric pressure. On account of this high pressure the materials in the inner part of the core remain in solid form. However, in the outer part of the core, the pressure is relatively low and consequently the material there is in molten state.

Q.23. What is meant by efficiency of a heat engine ? How much heat energy will have to be supplied to heat engine having efficiency of 30% to lift a mass of 100 kg through a heigh of 30 metres ? (g = 10 m/s²)
Ans23. Efficiency of a heat engine is defined as the percentage of heat energy which an engine can convert into mechanical energy.
Given efficiency = 30%
mass to be lifted,m = 100 kg
height through which mass is raised,h = 30 m
Work done = mgh
= 100 x 10 x30
= 30,000 J
                   Work done
Efficiency
                   energy supplied
    30,000 J

energy supplied
thus energy supplied
                  100
= 30,000 J x
                   30
= 1,00,000 J
= 100 kJ

Q.24 Name the type of orbits possessed by a remote sensing satellite & communication satellite. Describe their orbits. What is the function of a transponder in a communication satellite ?
Ans24. Remote sensing satellite has a sun synchronous orbit. This orbit is such that the satellite passes over a particular latitude at approximately the same local time.Thus the position of the satellite with reference to a place is synchronous with the elevation of sun at that place.

The orbit of communication satellite is geostationary.This orbit is such that the relative position of satellite does not change with respect to a fixed station on earth. The time period of revolution of the satellite around the earth is 24 hours.

Function of transponder in a communication satellite: It receives the signals from earth stations and transmits the amplified signals in different directions.

Q.25 With the help of diagrams describe the working of a diesel engine. In which stage is the working of diesel engine different from that of a petrol engine ?
Ans25. The working of a diesel engine can be divided into four stages (strokes):

(i) The Intake Stroke
# the diesel engine starts
# the piston P moves downwards in the cylinder
# a region of low pressure is created in the upper part of the cylinder
# the intake valve V₁ opens up
# air enters into the cylinder

(ii) The Compression Stroke
# when a sufficient amount of air has entered the cylinder the intake valve V₁ gets closed
# the piston is forced to move upwards
# the air present in the cylinder gets compressed excessively
# compression produces heat
# the air present in the cylinder becomes very hot

(iii) Expansion Stroke (or Power Stroke)
# having compressed the air, piston P reaches the upper part of the cylinder
# a fine spray of diesel oil is injected into the cylinder through the nozzle N
# due to the high temperature of air in the cylinder, diesel oil burns immediately
# the burning of diesel fuel produces large quantities of gases like CO, CO₂, H₂O
# a large amount of heat is also produced
# due to excessive heat, these gases expand rapidly
# the pressure of rapidly expanding hot gases pushes the piston downwards with a great force
# the moving piston pushes its piston rod R
# the piston rod in turn pushes the crank-shaft
# the crank-shaft turns the motor wheel

(iv) Exhaust Stroke
# the piston has been pushed to the bottom of the cylinder by the hot expanding gases in the expansion stroke
# the exhaust valve V₂ opens up
# due to the momentum of the rotating wheels of the vehicle, the piston is pushed upwards
# when the piston moves upwards, it expels the spent cold gases from the cylinder through the exhaust valve V₂.
# the exhaust valve V₂ gets closed,                         jump to top

the intake valve V₁ opens up again and the above four strokes of the diesel engine are repeated again and again.

In the intake stroke of a diesel engine only air enters into the cylinder whereas in the a petrol engine, a mixture of petrol vapour and air enters into the cylinder.

Charging/intake       Compression    Working       Exhaust

Q.26 An element has two allotropic forms A and B and belongs to group V of the periodic table. A is much darker in colour than B. Ignition temperature of A is 200°C and that of B is 30°C. What may A and B be? Which one of them reacts with (i) chlorine on heating but not in the cold, (ii) hot concentrated solution of NaOH producing a gas? Write the chemical equations for the reactions involved.
Ans26. Since the element belongs to group V, and the allotrope with higher ignition point is darker, it must be Phosphorous. A is "Red phosphorous" and B is "White or Yellow Phosphorous".

(i) Red phosphorous reacts with chlorine on heating, but not in cold:
2P + 3Cl₂ 2PCl₃
2P + 5Cl₂ 2PCl₅
(ii) Yellow phosphorous reacts with conc. NaOH and produces phosphene gas:
4P + 3 NaOH + 3 H₂O PH₃+ 3NaH₂PO₂

Q.27 "Faulty methods of cooking are responsible for deficiency of nutrition in food." Discuss.
Ans27. Faulty cooking is responsible for deficiency of nutrition in food, because:
(i) deep-frying destroys the nutrients, coagulates proteins, and burns carbohydrates,
(ii) over-cooking of food destroys the useful components of food and burns them,
(iii) washing of cut vegetables and fruits causes loss of water soluble vitamins and nutrients,
(iv) heating of milk substantially destroys the vitamins and coagulates the milk-proteins.

Q.28 Differentiate between biome and biosphere. Why is biosphere considered as a higher level in the organisation?
Ans28. Biome is a big unit, which includes all the ecosystems taken together in a geographical area. For example, in desert biomes or forest biomes one may find a pond, a lake, a grassland and even forest ecosystems.
Biosphere is still a bigger unit, which includes all the biomes, world over, taken together as a bigger unit constituting a single large self-sustaining biological system. All the life supporting regions of earth comprise biosphere.
Biosphere is referred to as a system, and is a higher level in the organization because it includes all the ecosystems on earth as well as biomes.

Q.29 What is hybridisation in relation to crops? Describe the process of hybridisation to produce an improved variety of wheat. Mention one advantage and one disadvantage of a high yield variety of wheat.
Ans29. Hybridisation is carrying out of cross breeding of varieties selected to incorporate the desired characters from two or more varieties in a same variety. For hybridisation of wheat It involved:
i) selecting two varieties of crops, which are known to possess at least one of the desired characteristics such as high yield or resistance to diseases;
(ii) cross breeding the varieties;
(iii) selecting the progeny with all the desired characters.
The advantage of HYV is: The yield of the dwarf wheat is substantially high than the traditional varieties
The disadvantage of HYV is: They require better inputs: more water and fertilisers, frequent .weeding and continuous use of pesticides.

Q.30 In a lake contaminated with pesticides, which one of the following organisms living in that lake will contain the maximum amount of the pesticide? Small fish, Zooplanktons, Big fish, phytoplanktons and Water birds. Define the process cited above. Name the substance whose accumulation in pelicans of Lake Michigan led to the formation of thin shells of their eggs.
Ans30. Water bird will have the maximum concentration of pesticides in its body, because it is at the top of the food-chain:
PhytoplanktonsZooplanktonsSmall fishBig fishWater bird

This phenomenon is called Biomagnification, which is the process of accumulation of higher concentration of harmful chemicals in the bodies of the organisms subsequently up in the trophic levels.

Q.31 With the help of a diagram, describe the experiment that established the relationship between mechanical energy and heat. Name the scientist who established this relationship. What observations were made by scientist in this experiment ?
Ans31: Jouel established the relationship between mechanical energy and heat.
Joule's apparatus consisted a copper calorimeter containing water.The weights connected to the paddles churned the water inside the calorimeter. As the weights fell they lost potential energy and the paddles gained kinetic energy as they turned.This kinetic energy was converted to heat which raised the temperature of the water inside.
The energy that the weights lost as they fell, was potential energy (mechanical energy). The energy that raised the temperature of the water was heat energy.

Joule ensured the equivalence of the two energies, and found that when the falling weights lost 4186 joule, the temperature of one kg of water went up by 1°C. Joule used a number of other methods to do mechanical work and converted it into thermal-energy and found the same equivalence of mechanical energy and heat:
4186 J = 1 cal

Q.32 Described the steps involved in the extraction of aluminium from bauxite using the electrolytic method. Draw a diagram of the electrolytic cell used. Why is some cryolite mixed with purified bauxite in this method?
Ans32. Aluminium is extracted from bauxite, which is primarily Aluminium oxide.

Bayer method is used to get pure aluminium oxide from bauxite ore. In this method the ore is treated with hot sodium hydroxide which forms sodium aluminate which is soluble in water. By filtration gangue is separated. Aluminium is precipitated as alumium hydroxide by acidifying the filtrate. Pure alumium oxide is then obtained by heating the aluminium hydroxide.
Al₂O₃ (from ore) + 3 NaOH NaAlO₂ + H₂O
                                                   Sodium aluminate

NaAlO₂ + HCl + H₂O Al(OH)₃ + NaCl
2 Al(OH)₃ Al₂O₃ + 3 H₂O
Al₂O₃ is reduced to aluminium by electrolytic method in a specially made electrolytic cell.

Aluminium                                            

The inside coke lining acts as a cathode and carbon rods as an anode. The cell is charged with a mixture of concentrated bauxite ore and cryolite (Na₃AlF₆). When current is passed through the cell the mixture melts because of the heat generated due to the resistance offered by the mixture. Molten mixture is then electrolysed.
The separated aluminium collects at the bottom of the cell.
Cryolite lowers down the melting temperature of bauxite and causes the melting of the charge (bauxite + cryolite).

Q.33 List two basic steps involved in preservation of food. Describe three common methods used for the preservation of fruits and vegetables. Name any two food preservatives commonly used in our country.
Ans33. The basic steps in Food Preservation are:
(a) Elimination of microrganisms responsible for spoilage,
(b) Creation of conditions unsuitable for microbial growth and action.

(b) Creation of conditions unsuitable for microbial growth and action.
(1) Bactericidal Methods: The bacteria are eliminated completely by cooking and canning.
(2) Bacteriostatic Methods: The bacteria and their enzymes are rendered inactive by dehydration,salting, and pickling.

Three commonest methods are:
(1) Dehydration and Sun-Drying: The fruits and vegetables are dried in the sun or by removing their water content under controlled conditions of temperature and humidity. Smoking is a process to dry meat, fish, and their products.

(2) Preservation by Salting and Sugar: Presence of a high concentration of salts ( 15%) or sugars ( 70%) drains out the water from food materials through osmosis and prevents their spoilage by inhibiting bacterial growth. Vinegar, oils, spices and citric acid are also used as preservatives on the same principles.

(3) Chemical Preservation: Two common chemical food preservatives used in our country are:
    (i) Benzoic acid, and
    (ii) Sulphur oxide.
Benzoic acid, or its sodium salt is used to preserve fruits, juices and squash at < 0.1% concentration. SO₂ is obtained from sodium metabisulphite by dissolving the latter in the fruit juice, or squash. It is used to preserve colourless fruits and fruity solutions.
Two commonest food preservatves used in our country are:
    (1) Benzoic acid, and
    (2) Sulphur oxide.