Chapter 5 – Towards Green Energy
1. Remake the table taking into account relation between entries in three columns.
| I | II | III |
|---|---|---|
Coal | Potential energy | Wind electricity plant |
Uranium | Kinetic Energy | Hydro electric plant |
Water Reservoir | Nuclear Energy | Thermal plant |
Wind | Thermal Energy | Nuclear power plant |
Ans:
| I | II | III |
|---|---|---|
Coal | Thermal Energy | Thermal plant |
Uranium | Nuclear Energy | Nuclear power plant |
Water Reservoir | Potential energy | Hydro electric plant |
Wind | Kinetic Energy | Wind electricity plant |
2. Which fuel is used in thermal power plant? What are the problems associated with this type of power generation?
Ans: In the thermal power plant coal is used as a fuel. Problems created by thermal power plant:
(i) The combustion of coal results in emission of gases like CO₂, NO₂, SO₂, which causes air pollution.
(ii) During combustion of coal, soot is formed thus carbon particles added to air can cause respiratory problems.
(iii) Large amount of coal is required for this plant which may deplete the coal reserves rapidly. In the shortage or lack of coal the thermal power plant could be shut down.
3. Other than thermal power plant, which power plants use thermal energy for power generation? In what different ways is the thermal energy obtained?
Ans:
(i) Thermal energy is used in power plants using coal, Uranium, Natural gas, (LPG and CNG) as fuels.
(ii) Generally, thermal power plants use coal to produce heat and chemical energy of coal is converted into heat during the combustion.
(iii) Apart from coal, natural gas, LPG and CNG are also used as fuel for the thermal power plant.
(iv) Nuclear power plants use uranium as the source of energy.
(v) In the nuclear power plant the nuclear fission of uranium results in the production of heat which is utilized for the production of steam.
(vi) In the solar thermal plant, the heat is obtained by concentrating solar radiations and then steam is produced.
4. Which type/types of power generation involve maximum number of steps of energy conversion? In which power generation is the number minimum?
Ans:
(i) The nuclear power plant has maximum steps for the generation of electricity.
(ii) The flow chart of nuclear power plant is as follows:
(iii) The transformation of energy in an electric generator using wind energy has minimum number of steps:
(iv) Stages in electric energy generation using wind energy:
5. Solve the following crossword puzzle.
a. Maximum energy generation in India is done using _____ energy.
Ans: Thermal
b. _____ energy is a renewable source of energy.
Ans: Wind
c. Solar energy can be called _____ energy.
Ans: Green
d. _____ energy of wind is used in wind mills.
Ans: Kinetic
e. _____ energy of water in dams is used for generation of electricity.
Ans: Potential
6. Explain the difference.
a. Conventional and Non-conventional Sources of energy.
Ans:
| Conventional energy sources | Non-conventional energy sources |
|---|---|
(i) Conventional energy sources are exhaustible. | (i) Non-conventional sources of energy are inexhaustible. |
(ii) Conventional sources of energy cause pollution. | (ii) Non – conventional sources of energy are pollution free. |
(iii) Conventional sources are used extensively by us. | (iii) Non-conventional sources of energy are not used as extensively as conventional sources. |
(iv) These sources require thousands of years to form. | (iv) They are abundantly available in nature. |
(v) Examples: Coal, Crude oil, Natural gas, etc. | (v) Examples: Solar energy, wind energy, bio-gas etc. |
b. Thermal electricity generation and solar thermal electricity generation.
Ans:
| Thermal electricity generation | Solar thermal electricity generation |
|---|---|
(i) In thermal power plants coal, natural gas, etc are used as sources (fuels). | (i) In a solar power plant, solar radiations are used as the source. |
(ii) Working at a thermal power plant can cause air pollution. | (ii) Solar power plants do not cause air pollution. |
(iii) The rate of electric power generation is very high. | (iii) The rate of electric power generation is very low. |
(iv) This energy source is not eco-friendly. | (iv) This energy source is absolutely eco-friendly. |
7. What is meant by green energy? Which energy sources can be called as green energy sources and why? Give example.
Ans:
(i) The eco-friendly energy is called green energy.
(ii) The energy production which does not cause any damage to the environment is actually green energy.
(iii) Solar energy, wind energy, hydroelectric energy do not harm the environment as there is no combustion involved and there is no air pollution caused.
(iv) Thus, energy obtained from these sources are called green energy.
8. Explain the following sentences.
a. Energy obtained from fossil fuels is not green energy.
Ans:
(i) Fossil fuels cause pollution during combustion.
(ii) Burning of coal results in emission of gases like carbon dioxide which is harmful to health.
(iii) Coal and oil release sulphur dioxide and soot, which causes problems related to respiration and acid rain.
(iv) As fossil fuels harm the environment they cannot be considered as green energy.
b. Saving energy is the need of the hour.
Ans:
(i) Energy is necessary to perform work.
(ii) Day by day the use of energy for various purposes is rising.
(iii) If we do not harness new sources of energy, the reserves of fossil fuels would get exhausted faster.
(iv) It is estimated that the current reserves would get over in nearly 200 years.
(v) If we save energy today, we may use it for a longer period of time.
(vi) Thus it is important to take every possible measure to save energy.
9. Answer the following questions.
a. How can we get the required amount of energy by connecting solar panels?
Ans:
(i) Solar cells contain the semiconductor Silicon
(ii) A Silicon solar cell of area 1 cm² can generate 30 mA of electricity and 0.5V potential difference is obtained.
(iii) If two solar cells are connected in series the potential difference get added to 1V but electric current remains the same.
(iv) If two solar cells are connected in parallel, the current becomes 60 mA but the potential difference remains the same. In this manner we can get the required potential difference and electric current.
b. What are the advantages and limitations of solar energy?
Ans:
Advantages of solar energy:
(i) Solar energy is a clean source of energy.
(ii) It is a sure source of energy.
(iii) It is an eco-friendly source of energy.
(iv) Since there is no combustion of fuel there is no pollution of air.
(v) This energy source is in-exhaustible.
(vi) Solar energy can be easily converted into electricity for use.
Limitations of using solar energy:
(i) Solar radiations are available only in the daytime.
(ii) Storage equipment is costly and the initial installation cost is very high.
(iii) Radiation intensity is not constant throughout the day, hence it is not an even or uniform source.
(iv) Solar panels occupy a lot of space, hence there is an issue of space for installation.
(v) It is not a concentrated source as solar energy is scattered.
(vi) Sunlight of 100 W/cm² can produce only 15 W power. i.e. the efficiency of equipment is 15% which is low.
10. Explain with diagram step-by-step energy conversion in
a. Thermal power plant
Ans:
(i) Water stored in a dam’s reservoir has potential energy.
(ii) When this water flows, the potential energy gets converted into Kinetic energy.
(iii) With the help of this Kinetic energy, the turbines are rotated.
(iv) The turbine in turn drives the generator to generate electricity.
b. Nuclear Power Plant
Ans:
(i) Solar energy is initially converted into heat by concentrating it.
(ii) The absorbed sunlight is utilized to boil water and steam is obtained.
(iii) Kinetic energy of steam is used to drive turbines.
(iv) The kinetic energy of a turbine is used to drive generators which produce electricity.
c. Solar thermal power plant
Ans:
(i) When fuel U-235 is bombarded with a neutron it becomes unstable and splits into Barium, Krypton and 3 neutrons with a lot of energy (200 MeV)
(ii) By using this energy, water is boiled to form steam.
(iii) By using kinetic energy of steam the turbine is rotated.
(iv) Then the kinetic energy of the turbine is used to rotate the generator and electricity is produced.
d. Hydroelectric power plant
Ans:
(i) Water stored in a dam’s reservoir has potential energy.
(ii) When this water flows, the potential energy gets converted into Kinetic energy.
(iii) With the help of this Kinetic energy, the turbines are rotated.
(iv) The turbine in turn drives the generator to generate electricity.
11. Give scientific reasons
a. The construction of turbine is different for different types of power plants.
Ans:
(i) Every power plant uses a different kind of source to rotate the turbine.
(ii) In thermal and nuclear power plants, steam produced rotates the turbine.
(iii) In hydroelectric power plant, flowing water is used to rotate turbines and wind is the medium in windmills.
(iv) Also the power output of every power plant is different.
(v) Hence, there should be turbines of different designs for different power plants.
b. It is absolutely necessary to control the fission reaction in nuclear power plants.
Ans:
(i) Nuclear power plants work on the principle of controlled chain reaction.
(ii) When slow moving neutrons strike the uranium nucleus, it splits into Barium and Krypton with the release of three neutrons and a tremendous amount of energy (200 MeV).
(iii) Three neutrons strike on three more uranium nucleus and fission continues creating tremendous energy which is harmful.
(iv) Reaction is controlled by using neutron absorbent material like boron steel and cadmium rods which absorb excess neutrons and heat generated can be used for welfare of mankind.
(v) Hence, 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.
Ans:
(i) Hydroelectric energy, solar energy and wind energy are all obtained without burning of a fuel.
(ii) They do not cause air pollution and are thus, eco-friendly.
(iii) Sunrise, rainfall, wind are natural phenomena.
(iv) These phenomena are constantly and continuously happening on earth.
(v) By setting up hydroelectric power plants, solar panels and windmills we can obtain these energies continuously, uninterrupted and at low cost. Hence, these sources are called renewable energy sources.
d. It is possible to produce energy from mW to MW using solar photovoltaic cells.
Ans:
(i) A silicon solar cell of dimension 1 cm2
generates a current of about 30 mA and potential difference of
about 0.5 V. Thus a silicon solar cell of dimension 100 cm² will generate about 3 A (30 mA/cm² × 100 cm² = 3000 mA) current and 0.5 V.
(ii) If solar cells are connected in series the potential difference gets added but current remains the same. If solar cells are connected in parallel the potential difference remains the same but the current generated is the summation of current from individual cells.
(iii) By using this principle we can obtain power of desired quantity.
(iv) We can decide the number of solar panels to be used and what type of combination we can have to get the required amount of electric power.
(v) Hence, solar photovoltaic cells can be used to obtain mW to MW power.
12. Draw a schematic diagram of solar thermal electric energy generation.
Ans:
13. Give your opinion about whether hydroelectric plants are environment friendly or not?
Ans:
(i) In the hydroelectric power plant, the kinetic energy of water gets converted into electricity.
(ii) The water stored in the dam possesses potential energy. As this water is allowed to flow, this energy gets converted into kinetic energy.
(iii) The kinetic energy of water is used to rotate the turbines and electricity is generated.
(iv) In this, since no fuel is burnt, there is no air pollution and thus it is eco-friendly
(v) Water mass does not get polluted as there are no effluents. This water can be used for agricultural purposes.
(vi) Compared to thermal and nuclear power plants the hydroelectric power plant is definitely eco-friendly.
(vii) Rehabilitation of people is necessary for people whose land is used for construction of dams.
14. Draw neat and labelled diagrams.
a. Energy transformation in solar thermal electric energy generation.
Ans:
b. One solar panel produces a potential difference of 18 V and current of 3 A. Describe how you can obtain a potential difference of 72 Volts and current of 9 A with a solar array using solar panels. You can use sign of a battery for a solar panel.
Ans:
Potential difference is 18 V and current is 3A. The requirement is potential difference of 72 V and current is 9A Voltage remains the same if connected in parallel and gets added if they are connected in series. Current remains the same if connected in series but adds if connected in parallel.
15. Write short note on
Electrical energy generation and environment.
Ans:
(i) The environmental impact of electricity generation is significant because modern society needs a large amount of electrical power.
(ii) The power is normally generated at power plants that convert some other kind of energy into electrical power.
(iii) Each system has some advantages and disadvantages, but many of them pose environmental concerns.
(iv) Thermal power plants emit CO₂, NO₂, SO₂ which cause air pollution.
(v) Nuclear power plants pose the threat of disposal of nuclear waste and radiation leakage.
(vi) Windmills and solar power plants are
eco-friendly but installation cost is high hence is used less frequently.
(vii) Hydroelectric power plants are Eco-friendly and generate sufficient electricity but rehabilitation of people whose land is used for construction of dam.