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Question 12 Marks
Write the uses of solar cells.
Answer
Use of solar cell:
  1. To provide electricity in artificial satellites and space probes.
  2. To provide electricity to remote areas where normal electricity transmission lines do not exist.
  3. To provide electricity to light houses iv. To operate traffic signals, watches, calculators and toys.
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Question 22 Marks
Write one use of wind energy.
  1. In the past.
  2. At present.
Answer
Use of wind energy.
  1. In the past – in flour mills.
  2. At present – for generating the electricity through wind-powered generators.
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Question 32 Marks
Write Einstein’s mass-energy equation. Give the meaning of each symbol which occurs in it.
Answer
Einstein’s equation: E=mc2 
where E is the amount of energy produced if mass m is destroyed, and c is the speed of light in vacuum.
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Question 52 Marks
Write any two advantages of using biogas.
Answer
Two advantages of biogas:
  1. Smoke-free cooking.
  2. High calorific value.
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Question 62 Marks
Why is tidal energy not likely to be a potential source of energy?
Answer
Tidal energy is not likely to be a potential source of energy because there are very few sites around the world which are suitable for building tidal barrages, and the rise and fall of seawater during high and low tides is not enough to generate electricity on a large scale.
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Question 72 Marks
Why is LPG considered a good fuel?
Answer
LPG is considered as good fuel because it has a high calorific value gives a smokeless flame.
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Question 82 Marks
Why is LPG considered a better fuel than coal?
Answer
LPG is considered as a better fuel than coal because it has a higher calorific value, while burning it does not produce any smoke.
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Question 92 Marks
Which of the two, nuclear fission and nuclear fusion, is made use of:
  1. For the production of electricity?
  2. For making a hydrogen bomb?
Answer
  1. Nuclear fission.
  2. Nuclear fusion.
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Question 102 Marks
Which of the two is a cleaner fuel: hydrogen or CNG? Why?
Answer
Hydrogen is a cleaner fuel because burning of hydrogen produces only water. which is harmless; but burning of CNG produces CO2 and water. CO2 produces greenhouse effect.
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Question 112 Marks
Which of the two causes serious air pollution and how?
Answer
Thermal power plant causes serious air pollution because it emits harmful gases and flyash into the air.
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Question 122 Marks
When the material A mined from the earth is heated strongly in an insufficient supply of air, it produces a solid fuel B which consists mainly of carbon. When another material C obtained from trees is heated in an insufficient supply of air, it produces another solid fuel D which also consists mainly of carbon. Name A, B, C and D.
Answer
  1. Coal (mined from the earth)Coal is mined from the earth.
  2. Coke. It consists mainly of carbon.
  3. Wood. It is obtained from trees.
  4. Charcoal. It consists mainly of carbon.
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Question 132 Marks
What kind of mirror, concave, convex or plane, would be best suited for use in a solar cooker? Why?
Answer
Concave and plane mirrors are used for making solar cooker because concave mirror converges a large amount of sun’s rays at a point that is required for high heating and plane mirror reflects the rays of light in the form of a strong beam of sunlight on the top of the box that is required for moderate heating.
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Question 142 Marks
What is the difference between a thermal power plant and a hydro power plant?
Answer
Difference between thermal power plant and hydro power plant:
  • Thermal power plant uses non-renewable sources of energy like coal, oil or gas; whereas hydro power plant uses renewable source of energy i.e. water.
  • Thermal power plant causes pollution due to the burning of fossil fuels; whereas hydro power plant is environment friendly.
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Question 152 Marks
What is the difference between a renewable and a non-renewable source of energy? Explain with examples.
Answer
Renewable source of energy can be used again and again endlessly, where as non-renewable source of energy cannot be renewed once used.
Ex. Renewable sources of energy are wind energy, ocean energy.
Non-renewable sources of energy are coal, fossil fuel.
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Question 162 Marks
What is solar constant? What is the value of solar constant?
Answer
The amount of solar energy received per second by one metre square area of the near earth space (exposed perpendicularly to the sun rays) at an average distance between the sun and the earth, is known as solar constant. Its value is 1.4kJ/s/ m2.
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Question 172 Marks
What is meant by conventional sources of energy? Write the names of two conventional sources of energy.
Answer
The traditional sources of energy which are familiar to most people are called conventional source of energy.
Example: Wood, coal etc.
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Question 182 Marks
What is meant by a renewable source of energy? Give two examples of renewable sources of energy.
Answer
A renewable source of energy is the one which is being produced continuously in nature and is inexhaustible.
Ex. wind energy, ocean thermal energy etc.
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Question 192 Marks
What is biomass? Give three examples of biomass.
Answer
The dead parts of plants and trees, and the waste material of animals are called biomass. It is the organic matter which is used as a fuel to produce energy. E.g., wood, agricultural wastes and cow dung.
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Question 202 Marks
What is biogas? Name the major component of biogas.
Answer
Biogas is a mixture of gases produced by anaerobic degradation of biomass in the presence of water but in the absence of oxygen. Methane is the major component of biogas.
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Question 212 Marks
What is a nuclear reactor? What is the fuel used in a nuclear reactor?
Answer
Nuclear reactor is a device designed to maintain a chain reaction producing a steady flow of neutrons generated by the fission of heavy nuclei. Uranium-235 is used as a fuel in a nuclear reactor.
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Question 222 Marks
What are the various steps which can be taken to control (or reduce) pollution caused by burning fossil fuels?
Answer
Pollution caused by the burning of fossil fuels can be controlled by the increasing the efficiency of combustion process and by using various techniques to reduce the escape of harmful gases and ash into the surrounding air.
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Question 232 Marks
What are the advantages of nuclear energy?
Answer
Advantages of nuclear energy:
  1. It produces a large amount of useful energy from a very small amount of a nuclear fuel.
  2. Once the nuclear fuel is loaded into the reactor, the nuclear power plant can go on producing electricity for two to three years at a stretch. There is no need of feeding the fuel again and again.
  3. It does not produce gases like CO2 or SO2.
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Question 242 Marks
What are the advantages and disadvantages of using nuclear fuel for generating electricity?
Answer
Advantages of using nuclear fuel: Electricity can be produced for almost two to three years with the same uranium fuel in a nuclear power plant.
Disadvantages of using nuclear fuel: The nuclear wastes produced by the fission of uranium235 during the generation of electricity are radioactive and extremely harmful.
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Question 252 Marks
What are fossil fuels? Give three examples of fossil fuels.
Answer
Natural fuels formed deep under the earth from the pre-historic remains of the organisms (like plants and animals) are called fossil fuels.
Example: Coal, petroleum and natural gas.
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Question 262 Marks
The pollution of air caused by burning petroleum fuels (like petrol and diesel) in vehicles can be controlled by fitting a device X in the exhaust system of vehicles.
  1. Name the device
  2. How does this device help in controlling air pollution?
Answer
  1. The device is a 'catalytic converter'.
  2. A catalytic converter converts the harmful gases from the exhaust of vehicles into harmless gases. For example, it converts carbon monoxide into carbon dioxide, and nitrogen oxide into nitrogen gas.
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Question 272 Marks
The energy in petrol originally came from the sun. Explain how it got into petrol.
Answer
Petrol is obtained from petroleum, which is a fossil fuel. Fossil fuels were originally made by sun’s energy because it was the sunlight of long ago that made plants and animals grow. So, the energy in petrol originally came from the sun.
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Question 282 Marks
Suggest a safe and efficient method for the disposal of biowastes and sewage materials. How is this method advantageous to us?
Answer
A safe and efficient method for the disposal of biowastes and sewage materials is to utilise them for producing biogas. This method is advantageous to us for getting energy and manure without polluting the environment.
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Question 292 Marks
State two ways in which the energy of sea-waves can be harnessed.
Answer
Sea-waves energy can be harnessed by by the following ways:
  1. By setting up floating generators in the sea which would move up and down with the seawaves and their movement would drive the generators to produce electricity.
  2. By letting the sea-waves move up and down inside large tubes so that when the waves move up, the air in the tubes is compressed and this compressed air can then be used to turn a turbine of a generator to produce electricity.
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Question 302 Marks
State two disadvantages of producing hydroelectricity.
Answer
Disadvantage of producing hydroelectricity.
  1. Large areas of land are required.
  2. Large eco-systems get destroyed.
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Question 312 Marks
State two disadvantages of geothermal energy.
Answer
Disadvantage of geo thermal energy:
  1. It is not available everywhere.
  2. Deep drilling in the earth is required, which is technically very difficult and expensive.
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Question 322 Marks
State two advantages of using wind energy for generating electricity.
Answer
Advantages of using wind energy for generating electricity:
  1. It does not cause any pollution.
  2. It is available free of cost.
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Question 332 Marks
State two advantages of producing hydroelectricity.
Answer
Advantage of producing hydroelectricity:
  1. It does not cause any environmental pollution.
  2. It uses the energy of flowing water, which is a renewable source of energy.
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Question 342 Marks
State two advantages of geothermal energy.
Answer
Advantage of geothermal energy:
  1. It is very economical to use.
  2. It does not cause any pollution.
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Question 352 Marks
State the disadvantages of nuclear energy.
Answer
Disadvantages of nuclear energy:
  1. The waste products of nuclear fission reactions are radioactive which keep on emitting harmful radiations for thousands of years and are difficult to store or dispose safely.
  2. Very high cost of installation is required.
  3. There is a limited availability of uranium fuel.
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Question 362 Marks
State any four characteristics of a good source of energy.
Answer
A non-renewable source of energy is defined as the source of energy which has accumulated in nature over a very, very long time and cannot be quickly replaced when exhausted.
Ex. Coal, petroleum etc.
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Question 372 Marks
Solar cells are used to provide the electric current to charge the batteries of a car driven by an electric motor. Describe the energy changes which take place.
Answer
The solar cells convert the energy from sunlight into electrical energy. This electrical energy is converted into chemical energy when the car batteries are charged. When these charged batteries are used, the chemical energy is converted into electrical energy. In the last stage, this electrical energy is converted into kinetic energy for the car by the electric motor that drives the car.
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Question 392 Marks
Mention two limitations of wind energy for generating electricity.
Answer
Limitations of wind energy:
  1. Wind energy farms cannot be established everywhere. They can be established only at those places where wind blows for most part of the year.
  2. Wind energy farms require large area of land for their establishment.
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Question 402 Marks
In many applications, solar cells are connected to rechargeable batteries. Why is this so?
Answer
The electricity made by the solar cells during day time is stored in rechargeable batteries so that it can be used later on, for example, at night.
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Question 412 Marks
In a solar water heater, why is the storage tank placed at a higher lever than the solar panel containing coils?
Answer
In a solar water heater, the storage tank is placed at a higher level than the solar panel containing coils because hot water is lighter and rises up.
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Question 422 Marks
If the energy received by 5m2 area in 10 minutes is 4200KJ, calculate the value of solar constant.
Answer
Area, A = 5m2 time, t = 10 min = 600 sec E = 4200kJ.

Solar constant $=\frac{\text{E}}{\text{(Axt.)}}.$

$=\frac{4200}{(5\times600)}.$

$=1.4\text{kJ/s/m}^2.$

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Question 432 Marks
If 25 atomic mass units (u) of a radioactive material are destroyed in a nuclear reaction, how much energy is released in MeV?
Answer
1 atomic mass unit = 931 MeV.
25 atomic mass unit = 931 × 25 MeV = 23275 MeV.
23275 MeV of energy is released.
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Question 442 Marks
How much solar energy will be received by 1m2 area in one hour if the solar constant be 1.4kW/ m2?
Answer
Solar constant is 1.4kW/ m or 1.4kJ/s/ m2.
Solar energy received by 1m2 area in 1s = 1.4kJ.
Solar energy received by 1m2 area in one hour (or 3600s) = 1.4 × 3600 = 5040kJ.
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Question 452 Marks
How much is this energy in MeV? (Speed of light = 3 × 10m/ s)
Answer
$1\text{MeV}=1.602\times10^{-13}\text{J}$
$1\text{J}=\frac{1}{1.602\times10^{-13}}\text{MeV}$
$4.5\times10^{14}\text{J}=\frac{4.5\times10^{14}}{1.602\times10^{-13}}=2.808\times10^{27}\text{MeV}$
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Question 462 Marks
How has the traditional use of wind energy been modified for our convenience?
Answer
Traditionally, wind energy was used through windmills to pump water from a well and to grind wheat into flour. But the traditional use has been modified and now it is used for the generation of electricity.
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Question 472 Marks
How has the traditional use of energy of flowing water been modified for our convenience?
Answer
Traditionally, the energy of flowing water has been used for rotating the water-wheels and for driving water-mills to grind wheat to make flour. The traditional use of energy of flowing water has been modified by improvements in technology and it is now used to generate electricity.
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Question 482 Marks
Fossil fuels are energy rich compounds of an element X which were originally made by the plants with help of sun's energy.
  1. Name the element X.
  2. Name another element which is usually found in combination with X in fossil fuels.
Answer
  1. Element X is carbon.
  2.  Another element found in combination with carbon in fossil fuels is hydrogen.
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Question 492 Marks
Explain why, natural gas is considered to be a good fuel.
Answer
Natural gas is considered to be a good fuel because it has a high calorific value, burns with a smokeless flame, causes no air pollution and does not produce any poisonous gas.
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Question 502 Marks
Explain how, wind energy can be used to generate electricity. Illustrate your answer with the help of a labelled diagram.
Answer
The fast moving wind strikes the wind turbine which starts rotating. The shaft of the wind turbine also rotates and drives the generator which produces electricity.
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Answer the questions.[Phy-2M] - Science STD 10 Questions - Vidyadip