Science Part ii Solutions Solutions for Class 10 Science Chapter 5 - Towards Green Energy

Answer:

Answer:

Coal is used in thermal power plant. Problems associated with this type of power generation are:

• Air pollution caused due to burning of coal: Burning of coal emits gases like carbon dioxide, sulphur oxide and nitrogen oxide which are harmful to living beings
• Release of soot particles in the environment: Along with the gases released due to burning of coal, soot particles are released in the environment which can cause fatal respiratory problems.
• Coal is non-renewable source of energy. So, this method of power generation will put a limit on the availability of coal in future.

Answer:

Other than thermal power plant, nuclear power plants, solar power plants use thermal energy for power generation. Different ways of generating thermal energy are:

• Using fossil fuels: By burning fossil fuels such as coal, petroleum, the chemical energy stored in them is converted into thermal energy.
• Using natural gas: Chemical energy in natural gas is converted into thermal energy.
• Using nuclear fuels: Controlled chain reaction in nuclear power plants releases huge amount of thermal energy.
• Using solar energy: Solar energy can be reflected and absorbed in aborbers where it gets converted to thermal energy. 
• Using geothermal energy: Underground water, sometimes, comes in contact with hot spots (where hot molten rocks are found), and thus steam is generated which is then collected via hot springs. Thus, geothermal energy is converted to heat energy.

Answer:

 The types of power generation involving maximum number of steps of energy conversion are:
(i) Thermal energy based power generation: It involves 5 steps of energy conversion.
$\mathrm{Chemical} \mathrm{energy} \mathrm{in} \mathrm{coal}\to \mathrm{thermal} \mathrm{energy}\to \mathrm{kinetic} \mathrm{energy} \mathrm{in} \mathrm{steam}\to \mathrm{kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{electrical} \mathrm{energy}$
(ii) Nuclear energy based power generation: It also involves 5 steps of energy conversion.
$\mathrm{Nuclear} \mathrm{energy}\to \mathrm{thermal} \mathrm{energy}\to \mathrm{kinetic} \mathrm{energy} \mathrm{in} \mathrm{steam}\to \mathrm{kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{electrical} \mathrm{energy}$

The power generation using solar photovoltaic cell involves least number of steps of energy conversion. It involves only two steps of energy conversion.
$\mathrm{Energy} \mathrm{in} \mathrm{sunlight}\to \mathrm{electric} \mathrm{energy}$

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a. 

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Green energy is that energy which does not pollute the environment and is renewable in nature. The energy sources such as sunlight, wind, rain, tides, etc. can be called as green energy. This is because these are readily available on Earth, can be naturally replenished and do not even harm the environment much.

Answer:

a. Fossil fuels are non renewable sources of energy. These are getting depleted rapidly. Also, the usage of the fossil fuels for energy generation adversely impacts the environment and living beings. Burning of fossil fuels like coal, natural gas etc. leads to emission of gases and soot particles in the environment which pollute the air and cause many respiratory diseases. For example, incomplete combustion of some fossil fuels leads to formation carbon monoxide which affects the health of living beings. Also, burning of fossil fuels releases carbon dioxide in the environment which is the main greenhouse gas. Thus, it can be said that energy obtained from fossil fuels is not green energy.

b. Yes, certainly energy conservation has become the need of the hour. We know our day to day life runs on electricity. Be it fans, lights, televisions, escalators, vehicles on roads or water supply to our homes, each and everything requires energy- "The Electrical Energy" for its working. Even the technology advancement has made it possible to supply electricity to most remote places. Thus, to produce such huge amount of electrical energy, we are getting more and more dependent on non-renewable sources of energy such as coal, petroleum, etc. It is observed that the rate at which these fuels are consumed is much greater than at which it is produced. So, if it continues like this, a day will come when we would get deprived of these sources of energy and thus will not even get the basic amenities of life. So, take a pledge to not waste energy wherever possible for the betterment of our and future generation.

Answer:

a. Many identical solar cells connected together forms a solar panel. Now, many such solar panels are connected in series in a form of solar string to get required voltage. Also, many such identical solar strings are connected in parallel to get the required current. Hence, in this way we get the required amount of energy by connecting solar panels.

b. Advantages of solar energy:

• Solar energy is green energy i.e. it is renewable and does not cause pollution.
• Solar panels for the generation of electricity requires less maintenance.
• With the help of solar energy, electricity is possible to be generated even in the most remote, inaccessible locations where electric power lines cannot be laid.

• Electricity generation based on solar energy is weather dependent and hence it is less reliable. In winters and in cloudy days, the production becomes less. 
• The whole set-up of the panels requires lot of space to generate considerable amount of electricity. 
• The initial cost of a solar panel is sufficiently high.

Answer:

a. Water is heated in a boiler. Using the thermal energy released due to burning of coal, steam of very high temperature and pressure
is generated. The energy in the steam drives the turbine. Thus, the generator connected to the turbine rotates and electrical energy is produced.
$\mathrm{Chemical} \mathrm{energy} \mathrm{in} \mathrm{coal}\to \mathrm{Thermal} \mathrm{energy}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{steam}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{Electrical} \mathrm{energy}$


b. Nuclear power plants consist of nuclear reactors. These reactors use uranium rods as fuel and heat is generated by the process of nuclear fission. Neutrons smash into the nucleus of the uranium atoms, which roughly split into half and release energy in the form of heat. Carbon dioxide gas is pumped through the reactor to take the heat away. The hot gas then heats water to form steam. This steam drives the turbines of generators to produce electricity. Thus, the steps of energy conversion are:
$\mathrm{Nuclear} \mathrm{energy}\to \mathrm{Thermal} \mathrm{energy}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{steam}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{Electrical} \mathrm{energy}$

c. Following energy conversion takes place in the solar thermal power plant:


$\mathrm{Thermal} \mathrm{energy} \mathrm{in} \mathrm{radiation}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{steam}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{Electrical} \mathrm{energy}$

d. In hydroelectric power plant, the potential energy in water stored in dam is converted into kinetic energy of water. Fast flowing water is brought from the dam to the turbine at the bottom of the dam. The kinetic energy of the flowing water drives the turbine. The turbine
in turn drives the generator to generate electricity.
$\mathrm{Potential} \mathrm{energy} \mathrm{in} \mathrm{water}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{flowing} \mathrm{water}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{Electrical} \mathrm{energy}$

Answer:

a. The construction of turbine is different for different types of power plants. This depends on the type of energy source used for driving the turbine. Like in thermal power plants, steam turbine is used whereas in hydro-power plant, water turbine is used.

b. If fission reaction in nuclear power plants is not controlled, then enormous amount of heat released during this process will lead to explosion of the plant and cause fatal destruction to environment and mankind. Thus, it is absolutely necessary to control the fission reaction in nuclear power plants.

c. Hydroelectric energy, solar energy and wind energy are called renewable energies because they are abundant in nature and can be regenerated or replenished again and again. These will never extinct even with their excessive use.

d. Solar photovoltaic cells can be arranged according to the requirement of electric power. If power requirement is within mW, use of few number of photovoltaic cells will be able to achieve this much power. But, if the requirement of power is in MW, then large number of cells are grouped together to form a solar panel. Then, large number of solar panels are connected in series and parallel to get the required electric power. Thus, it is possible to produce energy from mW to MW using solar photovoltaic cells.

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The schematic diagram of solar thermal electric energy generation is as follows:

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No waste products and harmful gases are released in water bodies and atmosphere when power is generated using hydroelectric power plants. Also, water is available in plenty on Earth and is renewable. Hence, there is no fear of this energy source dying out. Thus, it has no harmful effects on environment and hence is environment friendly.

Answer:

a.
 
$\mathrm{Thermal} \mathrm{energy} \mathrm{in} \mathrm{radiation}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{steam}\to \mathrm{Kinetic} \mathrm{energy} \mathrm{in} \mathrm{turbine}\to \mathrm{Electrical} \mathrm{energy}$

b. We can obtain a potential difference of 72 V by forming a string of 5 solar panels in series. Now, to obtain current of 9 A, connect 3 such identical strings in parallel. The same has been shown below.
 

Answer:

Today electrical energy generation has become the need of the hour. We cannot imagine our life without electricity. We have been able to generate electrical energy by various methods. In these methods, a generator is present which works on the principle of electromagnetic induction. A turbine is used to rotate this generator and this turbine itself is rotated with the help of an energy source. This energy source can be renewable source such as wind, sunlight, nuclear fuels etc. as well as non-renewable source such as coal, petrol, water etc. The energy sources such as wind, sunlight have proved to be green sources as they do not pollute the environment and are economical too. But the use of fossil fuel such as natural gas, coal, nuclear energy etc. as energy source has harmful effects on environment. The harmful radiations emitted from the nuclear waste has fatal effect on the environment and humans. Even the release of soot particles and various greenhouse gases such as carbon dioxide, carbon monoxide on burning or incomplete burning of fossil fuels affects the health of living beings as well as the environment adversely. Also, the release of these greenhouse gases is day by day increasing the danger of global warming. We need to as soon as possible find suitable environment friendly substitutes to fossil fuels to save our Earth.