Non-conventional Sources of Energy Questions in English

(N/A) Traditionally,waterfalls were used as a source of potential energy,which was converted into electricity with the help of turbines. Since waterfalls are limited,large-scale water dams have been constructed. Nowadays,hydroelectric dams are used to harness the potential energy of stored water. In these dams,water falls from a height onto a turbine,which rotates to produce electricity.
Earlier,windmills were primarily used to perform mechanical work,such as drawing water from a well or grinding grain. Today,modern windmills (wind turbines) are used to generate electricity. In these systems,the kinetic energy of the wind is harnessed to rotate the blades,which in turn rotate the turbine of an electric generator to produce electricity.

(N/A) The forms of energy that can be obtained from the ocean are tidal energy,wave energy,and ocean thermal energy. There are several limitations in order to harness these energies.
$(i)$ Tidal energy depends on the relative positioning of the Earth,the moon,and the Sun.
$(ii)$ High dams are required to be built to convert tidal energy into electricity.
$(iii)$ Very strong waves are required to obtain electricity from wave energy.
$(iv)$ To harness ocean thermal energy efficiently,the difference in the temperature of surface water (hot) and the water at depth (cold) must be $20\,^{\circ}C$ or more.

(B) Geothermal power plants use the heat of the Earth to generate electricity. This heat energy of the Earth is known as geothermal energy.
When there are geological changes,the molten rocks present in the core of the Earth are pushed to the Earth's crust. This forms regions of hot spots. Steam is generated when the underground water comes in contact with these hot spots,forming hot springs. This trapped steam is used to generate electricity in geothermal power plants.

(N/A) The advantages of nuclear energy are as follows:
$(a)$ A large amount of energy is produced per unit mass.
$(b)$ It does not produce smoke, making it a clean source of energy.
$(c)$ The fission of one atom of uranium produces $10$ million times the energy released by the burning of one atom of carbon.
$(d)$ The fusion of four hydrogen atoms produces a huge amount of energy, approximately equal to $27 \, \text{MeV}$.

(N/A) Two renewable sources of energy are as follows:
$(a)$ Sun: The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium and other heavy elements. $A$ large amount of hydrogen is present in the Sun,allowing it to replenish on its own. The Sun is expected to continue burning for another $5$ billion years. Hence,solar energy is a renewable source of energy.
$(b)$ Wind: Wind energy is derived from air blowing at high speeds. Wind energy is harnessed by windmills to generate electricity. Wind is caused by the uneven heating of the Earth's surface by the Sun. Since this heating process will continue as long as the Sun exists,wind energy will remain available indefinitely.

(C) Wind energy is harnessed using windmills.
One of the primary limitations is that a windmill requires a minimum wind speed of more than $15 \,km/h$ to generate electricity effectively.
Additionally,to generate a significant amount of power,a large number of windmills are required,which necessitates a vast land area for the establishment of wind farms.

(D) The primary limitation of extracting energy from ocean waves is that it requires very strong and consistent ocean waves to be economically and technically viable.
Additionally,the technology for harnessing wave energy is still in the developmental stage,making the installation and maintenance costs very high.
Furthermore,these power plants can only be set up in specific coastal locations where wave intensity is sufficient.

(D) The limitations of extracting energy from tides are as follows:
$1$. It requires very high tides to generate a significant amount of energy,which are not available everywhere.
$2$. The occurrence of tides is dependent on the relative positions of the Sun,the Moon,and the Earth,making the energy supply intermittent and not constant.

(C) Ocean thermal energy conversion $(OTEC)$ plants operate on the principle of the temperature difference between the warm surface waters of the ocean and the colder deep waters.
At the surface,the water is heated by solar radiation,while the water at depths of $2 \ km$ or more is significantly colder.
This temperature gradient is used to operate a heat engine,which produces electricity.
Therefore,ocean thermal energy is specifically due to the temperature difference at different levels in the ocean.

(A) Wind power is harnessed by placing windmills in open spaces where wind blows at high speeds. Therefore,the statement that it is expected to harness wind power to a minimum in open space is incorrect. Windmills are specifically designed to be placed in open areas to maximize the capture of kinetic energy from the wind. The source of wind power is the kinetic energy of moving air,not potential energy. The rotation of the blades is used to drive a turbine,which in turn generates electricity.

(N/A) The need to harness non-conventional sources of energy arises due to the following reasons:
$(i)$ The demand for energy is continuously increasing due to the improvement in the quality of life and the rapid growth of the human population.
$(ii)$ Conventional sources of energy,such as fossil fuels,are limited in nature and are being depleted at a fast rate,making them unsustainable for the long term.

(N/A) Two different ways of harnessing energy from the ocean are:
$1$. Tidal Energy: This is generated by utilizing the rise and fall of ocean water levels due to the gravitational pull of the moon and the sun. Dams are constructed across narrow openings of the sea to trap water during high tide and release it during low tide to rotate turbines.
$2$. Wave Energy: This is harnessed by capturing the kinetic energy of ocean waves. Various devices are used to convert the oscillating motion of waves into mechanical energy, which then drives a generator to produce electricity.
$3$. Ocean Thermal Energy Conversion $(OTEC)$: This method utilizes the temperature difference between the warm surface water of the ocean and the colder deep water to run a heat engine and generate electricity.

(N/A) $(i)$ Solar cells have no moving parts.
$(ii)$ They require very little maintenance.
$(iii)$ They can be set up in remote and inaccessible areas where laying power transmission lines is difficult or expensive.

(C) The limitations of wind energy are as follows:
$1$. Wind speed is erratic and not constant,which means energy cannot be harnessed continuously.
$2$. Wind farms require very large areas of land to be effective.
$3$. The initial cost of setting up wind turbines is high.

(N/A) Solar energy can be harnessed using devices like solar cookers,solar water heaters,and solar cells. Solar cookers and heaters use reflectors to concentrate sunlight,while solar cells convert solar energy directly into electricity.
Limitations of using solar energy:
$1$. It is only available during the daytime and is less effective on cloudy or rainy days.
$2$. Solar energy devices require large surface areas for installation and can be expensive to set up initially.
Overcoming these limitations:
$1$. To address the issue of availability,energy storage systems like batteries are used to store electricity generated by solar cells for use during the night or cloudy days.
$2$. Research into advanced materials and mass production of solar cells is helping to reduce costs and improve efficiency,making solar energy more accessible.

(N/A) The need for harnessing non-conventional sources of energy arises because:
$1$. Fossil fuels are finite and are depleting rapidly due to high consumption.
$2$. The global population is increasing, leading to a higher demand for energy.
$3$. There is a need to improve the quality of life and reduce environmental pollution caused by burning fossil fuels.
Energy can be harnessed from the sea in the following ways:
$1$. Tidal Energy: This is harnessed by constructing dams across a narrow opening to the sea. The rise and fall of sea levels during high and low tides rotate turbines to generate electricity.
$2$. Wave Energy: This is harnessed by trapping the kinetic energy of waves near the seashore to rotate turbines or drive other mechanisms.
$3$. Ocean Thermal Energy Conversion $(OTEC)$: This utilizes the temperature difference between the warmer surface waters of the ocean and the colder deep waters to operate heat engines and generate electricity.

(N/A) The two non-conventional sources of energy are:
$(i)$ Geothermal energy
$(ii)$ Nuclear energy

(N/A) To generate electric power using a windmill,the wind speed must be higher than $15 \, km/h$. This minimum velocity is necessary to overcome the inertia of the blades and the internal friction of the generator system to produce a useful amount of electricity.

(N/A) biogas plant is considered a safe and efficient method of waste disposal for the following reasons:
$1$. It effectively manages organic waste,such as animal dung and agricultural residues,by converting them into useful energy.
$2$. The process produces biogas,which is a clean fuel that burns without smoke and leaves no harmful residue,thereby reducing air pollution.
$3$. The remaining slurry,after the production of biogas,is rich in nitrogen and phosphorus,making it an excellent organic manure for crops.
$4$. It helps in maintaining sanitation by disposing of waste in a controlled environment,which prevents the breeding of pathogens.

(N/A) The two elements commonly used in the fabrication of solar cells are:
$(i)$ Silicon $(Si)$: It is the primary semiconductor material used to form the $p-n$ junction in photovoltaic cells.
$(ii)$ Silver $(Ag)$: It is used to create the electrical contact grids on the surface of the solar cell to collect the generated current.

(N/A) The special technique used for mounting solar cell panels involves installing them on specially designed inclined roofs or structures.
Advantages:
$1$. It ensures that the solar panels are oriented towards the sun,allowing for maximum exposure to sunlight.
$2$. This inclination increases the intensity of solar radiation incident on the panels,thereby enhancing the efficiency of energy conversion.
$3$. It helps in preventing the accumulation of dust,debris,or water on the surface of the panels.

(C) Geothermal energy is considered a non-conventional renewable source of energy.
It is derived from the heat stored within the Earth's crust.
Unlike solar or wind energy,which are intermittent,geothermal energy provides a constant and reliable supply of power,allowing it to be harnessed for $24$ hours a day throughout the year.

(N/A) Solar energy manifests itself in the oceans primarily in the following two forms:
$(i)$ Ocean thermal energy: This is due to the temperature difference between the warm surface water and the colder deep water.
$(ii)$ Wave energy: This is caused by the wind blowing across the surface of the ocean,which is ultimately driven by solar heating of the atmosphere.

(B) In an ocean thermal energy conversion $(OTEC)$ plant,the energy is harnessed by utilizing the temperature difference between the warm surface water and the cold water found at depths of up to $2\, km$.
For the efficient operation of such a plant,a minimum temperature difference of $20^{\circ} C$ is required between the surface water and the deep-sea water.

(B) Hot spots are specific regions within the Earth's crust where molten rocks (magma) originating from deeper,hotter layers of the Earth are pushed upward due to high pressure and temperature.
These molten rocks get trapped in these crustal regions,creating localized areas of intense heat.
This geothermal energy can be harnessed for various purposes,such as generating electricity.

(C) An eco-friendly activity is one that does not harm the environment or contributes to sustainable development.
$A$. Using a car for transportation increases carbon emissions,which contributes to global warming.
$B$. Using polybags (plastic bags) is harmful as they are non-biodegradable and cause pollution.
$C$. Using windmills to generate power for irrigation is an eco-friendly activity because it utilizes renewable energy (wind energy) and does not produce harmful emissions.
$D$. Using chemical dyes for coloring clothes often leads to water pollution due to the discharge of toxic effluents into water bodies.
Therefore,the correct option is $C$.

(N/A) Advantages of a solar cooker:
$1$. It uses solar energy,which is an inexhaustible,clean,and renewable source of energy.
$2$. Solar energy is free and available in unlimited amounts,making the operation of a solar cooker cost-effective.
$3$. It does not cause any environmental pollution.
Disadvantages of a solar cooker:
$1$. The initial cost of purchasing a solar cooker can be high.
$2$. It does not work without direct sunlight. Therefore,it is ineffective on cloudy days or during the night.
$3$. Cooking food in a solar cooker is a slow process compared to conventional methods.
Places with limited utility:
Solar cookers have limited utility in regions where days are very short,or in areas that experience heavy cloud cover or frequent rainfall throughout the year,as they rely entirely on solar radiation.

(N/A) Renewable sources of energy are those that can be replenished naturally over a short period of time. Two examples of renewable sources of energy are:
$1$. Solar energy: Energy derived from the sun.
$2$. Wind energy: Energy derived from the movement of air.

(N/A) Two activities from our daily life in which solar energy is utilized are:
$1$. Drying of food grains and clothes.
$2$. Obtaining salt from sea water through the process of evaporation.

(N/A) The two materials commonly used to make solar cells are $Silicon$ and $Selenium$. $Silicon$ is the most widely used semiconductor material for manufacturing photovoltaic cells due to its abundance and efficiency. $Selenium$ is also used in specific types of solar cells.

(N/A) Solar energy manifests itself in oceans primarily in the following two forms:
$1$. Ocean Thermal Energy: This is caused by the temperature difference between the warm surface water and the colder deep water of the ocean.
$2$. Tidal Energy: This is caused by the gravitational pull of the Moon and the Sun on the Earth's oceans,which creates the rise and fall of sea levels.

(N/A) Solar cells are used in various fields due to their ability to convert solar energy into electricity. Four such areas are:
$(i)$ Artificial satellites and space probes.
$(ii)$ Radio or wireless transmission systems in remote areas.
$(iii)$ Traffic signals and street lighting.
$(iv)$ Research centres and calculators.

(B) In a semiconductor,the energy gap between the valence band and the conduction band is small. When light (photons) falls on the semiconductor,the electrons in the valence band absorb energy and jump to the conduction band. This process increases the number of free charge carriers (electrons and holes),which leads to an increase in the electrical conductivity of the semiconductor.

(B) Geothermal energy is the heat energy generated and stored within the Earth.
This heat originates from the original formation of the planet and the radioactive decay of materials.
It is harnessed by tapping into steam or hot water reservoirs found beneath the Earth's surface to generate electricity or for direct heating purposes.

(N/A) solar cell is a device that converts incident solar light energy directly into electrical energy in $DC$ form.
It is also known as a solar photovoltaic cell ($PV$ cell).

(A) solar cell is a device that converts solar energy directly into electricity. The most common material used for manufacturing solar cells is $Silicon$ $(Si)$. Sometimes,other semiconductor materials like $Gallium$ $(Ga)$ (often in the form of $Gallium$ $Arsenide$) are also used to increase efficiency.

(B) modern solar cell typically converts about $15\%$ to $20\%$ of the incident solar energy into electricity. While some high-efficiency research cells can reach higher values, the standard commercial efficiency range is generally considered to be around $15-20\%$.

(B) solar panel is a device that consists of a large number of solar cells connected in a specific arrangement (series or parallel) to generate a higher amount of electricity. These cells are mounted on a frame to capture sunlight and convert it into electrical energy.

(D) Solar cells are semiconductor devices that convert sunlight directly into electricity.
They are widely used in artificial satellites and space probes because they provide a reliable and long-lasting source of power in space where other conventional energy sources are unavailable.
Additionally,they are also used in calculators,watches,and street lighting.

(N/A) The two main merits of solar cells are:
$1$. They provide a clean and pollution-free source of energy as they do not emit any harmful gases.
$2$. They are noiseless in operation and require very low maintenance,making them a safe and sustainable energy option.

(B) Tidal energy is a form of hydropower that converts the energy obtained from tides into useful forms of power,mainly electricity.
It is generated due to the gravitational pull of the Moon and the Sun on the Earth's oceans,which causes a periodic rise and fall in the water level.
The difference in the levels of ocean water between high-tide and low-tide is harnessed to drive turbines.

(B) Ocean thermal energy is the energy available due to the difference in temperature between the water at the surface of the ocean and the water at deeper levels.
In this process,the warm surface water is used to boil a volatile liquid like ammonia,and the resulting vapor is used to run a turbine to generate electricity.
The cold water from the deeper layers is then pumped up to condense the vapor back into a liquid,completing the cycle.

(B) Geothermal energy is the heat energy originating from the Earth's core.
It is stored in the form of hot water springs (geysers) and molten rock,known as magma,located deep beneath the Earth's surface.
When this magma reaches the surface,it is called lava,which can cause volcanic eruptions.

(B) The fuels used in atomic power plants are known as nuclear fuels. These materials,such as $U^{235}$ (Uranium-$235$) or $Pu^{239}$ (Plutonium-$239$),undergo nuclear fission reactions to release a large amount of energy,which is then converted into electricity.

(N/A) The chief component of solar cells is $Silicon$.
Solar cells convert solar energy (light energy) into electric energy.

(B) The reaction responsible for the large energy production in the sun is nuclear fusion.
In this process,lighter atomic nuclei,primarily hydrogen,combine to form heavier nuclei,such as helium,releasing a tremendous amount of energy in the form of heat and light.

(N/A) $(i)$ It produces precious fuel from waste material that would otherwise be discarded.
$(ii)$ It helps in controlling water pollution by treating the sewage.
$(iii)$ The residual sludge after gas production serves as a nutrient-rich manure for agriculture.

(N/A)

Box type solar cooker	Reflector type solar cooker
$1.$ It does not concentrate solar energy at one point as a plane reflector is used.	$1.$ It concentrates energy at one point as a concave reflector is used.
$2.$ It can attain temperatures in the range of $100^{\circ}C$ to $140^{\circ}C$.	$2.$ It can attain temperatures in the range of $500^{\circ}C$ to $550^{\circ}C$.

(D) Harnessing of tidal energy poses many problems.
$1$. The rise and fall of water during tides is not high enough in most coastal areas to generate electricity on a large scale.
$2$. There are very few sites globally that are geographically suitable to build dams for tidal power plants.
$3$. High construction and maintenance costs make it less economically viable compared to other renewable sources.
It is for these reasons that tidal energy is not likely to be a major source of energy.

(N/A) Energy manifests itself in the oceans in the following forms:
$(i)$ Tidal energy: Energy derived from the rise and fall of ocean tides.
$(ii)$ Ocean thermal energy: Energy derived from the temperature difference between the warm surface water and the cold deep-sea water.
$(iii)$ Wave energy: Energy derived from the movement of ocean waves.
Out of these,Ocean thermal energy is utilised in the $OTEC$ (Ocean Thermal Energy Conversion) systems.