Mix Examples - Sources of Energy Questions in English

(N/A) $(i)$ Animal dung contains important nutrients that can be used as manure. When it is used directly as a fuel,these nutrients are completely lost due to oxidation.
$(ii)$ Combustion of animal dung produces a significant amount of smoke,which leads to air pollution.

(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) Natural gas is a naturally occurring mixture of methane (approx $85 \%$),ethane $(10 \%)$,propane $(3 \%)$,and butane $(2 \%)$. Other non-combustible gases like $CO_2$,$N_2$,and $O_2$ may also be present in the mixture.
Natural gas is formed by the action of heat,pressure,and microorganisms on buried organic matter over millions of years.

(A) $LPG$ (Liquefied Petroleum Gas) primarily consists of hydrocarbons like $n$-Butane,Isobutane,Propane,and Ethane.
It is obtained as a byproduct during the refining of crude oil or from natural gas wells.
Inside the cylinder,the gas is kept under very high pressure,which causes it to exist in a liquid state.
When the valve of the cylinder is opened,the gas is released into the burner where the pressure drops significantly,causing the liquid to vaporize and appear as a gas.

(N/A) Fossil fuels are the remains of plants and animals that were buried deep underground millions of years ago.
$1$. Plants capture solar energy through the process of photosynthesis and convert it into chemical energy stored in their tissues.
$2$. Animals obtain this energy by consuming plants or other animals that have consumed plants.
$3$. When these organisms died and were buried under high pressure and temperature over millions of years,their remains were converted into fossil fuels like coal,petroleum,and natural gas.
Therefore,the chemical energy stored in fossil fuels is essentially the solar energy that was trapped by plants long ago.

(N/A) The agents responsible for decomposing animal dung into biogas are $Anaerobic$ microorganisms (methanogens).
The process involves the following steps:
$1$. Mixing: Animal dung and water are mixed in a $1:1$ ratio to form a slurry in the mixing tank.
$2$. Digestion: The slurry is fed into a digester tank,which is a sealed,oxygen-free chamber. Here,$Anaerobic$ microorganisms break down the organic matter in the dung,producing biogas (primarily methane).
$3$. Collection and Usage: The produced biogas is collected in a gas holder and supplied for use. The remaining slurry,known as spent slurry,is removed and used as a nutrient-rich manure.

(N/A) $(i)$ They have higher thermal efficiency and produce significantly less smoke,which improves indoor air quality.
$(ii)$ They are scientifically designed to ensure complete combustion of fuel,leading to lower fuel consumption and reduced environmental pollution.

(N/A) The floating gas holder type biogas plant is considered less advantageous for the following reasons:
$(i)$ The floating gas holder type biogas plant is expensive because it is constructed using steel.
$(ii)$ There is a higher risk of gas leakage due to potential defects in welding or the corrosion of the steel components over time.
$(iii)$ It requires frequent repairs and painting to prevent rust,which significantly increases its overall maintenance cost.

(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 $550^{\circ}C$.

(N/A) Advantages:
$(a)$ Production of cheap electricity without causing pollution.
$(b)$ Dams are used for irrigation and flood control.
Disadvantages:
$(a)$ Large land areas get submerged,leading to the loss of biodiversity and displacement of local populations.
$(b)$ It adversely affects the ecosystem of adjoining areas as well as areas downstream by altering natural water flow and sediment transport.

(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) Wind energy farms can be set up only at specific locations due to the following reasons:
$(i)$ They require locations where wind blows for the greater part of the year.
$(ii)$ The wind must be strong and steady,typically having a speed of at least $15\, km\, h^{-1}$ to rotate the turbine effectively.
$(iii)$ $A$ large,open,and free space is required to install multiple wind turbines without obstruction.
Since these specific environmental and geographical conditions cannot be satisfied everywhere,wind energy farms can only be established at selected locations.

(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.

(N/A) Charcoal is considered a better fuel than wood because:
$(i)$ Charcoal burns easily without producing smoke.
$(ii)$ It produces twice as much heat as the same mass of wood.
The disadvantage of converting wood into charcoal is that during the destructive distillation of $1\, kg$ of wood,only $0.25\, kg$ of charcoal is obtained. In other words,the conversion process is inefficient and costly,making charcoal an expensive fuel.

(N/A) The sequence of energy transformations that occur during the generation of electricity from water stored in a dam is as follows:
$(i)$ Solar energy is converted into potential energy $(PE)$ of water vapour as water evaporates from oceans, rivers, and lakes. This vapour forms clouds and eventually falls as rain or snow on mountains.
$(ii)$ When rain falls or snow melts, the potential energy of the water is converted into kinetic energy $(KE)$ as it flows into streams and rivers.
$(iii)$ When this flowing water is collected and stored in a dam, its kinetic energy is converted back into potential energy $(PE)$ due to its height.
$(iv)$ When water is released from the dam, this potential energy is converted into kinetic energy $(KE)$ as the water rushes downwards.
$(v)$ The kinetic energy of the falling water rotates the turbines, which in turn drive a generator to produce electricity. Thus, the original source of this energy is solar energy.

(N/A) Fossil fuels are energy sources formed from the remains of ancient plants and animals that were buried under the Earth's crust millions of years ago and underwent decomposition under high pressure and temperature.
The three common fossil fuels are: $(i)$ Coal,$(ii)$ Petroleum (Oil),and $(iii)$ Natural Gas.

(N/A) Obtaining energy from nuclear fusion reactions is preferable to obtaining energy from nuclear fission reactions for the following reasons:
$(i)$ For a given mass of fuel,the energy released during nuclear fusion is significantly greater than the energy released during nuclear fission.
$(ii)$ Nuclear fission produces radioactive waste,which poses a significant challenge for safe disposal and long-term storage. In contrast,nuclear fusion does not produce such hazardous radioactive waste,making it a cleaner and safer alternative.

(N/A) The two ways by which water can be used to produce hydroelectricity are:
$(i)$ Using the potential energy of water stored at a height in dams,which is released to fall on turbines.
$(ii)$ Using the kinetic energy of ocean tides (the rise and fall of sea water) to rotate turbines for electricity generation.

(N/A) Solar energy is the primary cause of wind,which is the kinetic energy of moving air. The uneven heating of the Earth's surface by the Sun creates pressure differences,leading to the movement of air (wind). $A$ windmill captures this kinetic energy of the wind to rotate a turbine,which is then used to generate electricity. Therefore,wind energy is essentially an indirect form of solar energy converted into electrical energy.

(N/A) Solar energy is stored in the oceans in the forms of $Ocean \ Thermal \ Energy$ $(OTE)$,$Wave \ Energy$,and $Tidal \ Energy$.
Two forms that can be harnessed to obtain energy in a usable form are:
$1$. $Ocean \ Thermal \ Energy$ $(OTE)$: This is harnessed by utilizing the temperature difference between the warm surface water and the cold deep water to run turbines for electricity generation.
$2$. $Wave \ Energy$: This is harnessed by using the kinetic energy of waves to move floating devices or air columns,which in turn drive turbines to generate electricity.

(N/A) The two reasons are:
$(i)$ Production of electricity from water is pollution-free,whereas burning coke causes significant air pollution.
$(ii)$ Flowing water is a renewable source of energy,meaning it is naturally replenished,while coke is a non-renewable fossil fuel that will eventually be exhausted.

(N/A) The places where natural gas is found in India are Tripura,Jaisalmer,the off-shore area of Bombay,and the Krishna-Godavari Delta.
Natural gas is called a clean fuel because:
$(i)$ It does not produce harmful gases upon combustion.
$(ii)$ It burns without smoke and does not leave any residue after burning.

(N/A) fuel is any material that releases energy,typically in the form of heat,when it undergoes combustion or chemical reaction.
Primary Fuels: These are naturally occurring substances that are used directly as a source of energy without any significant processing. Examples include wood,coal,and petroleum.
Secondary Fuels: These are fuels derived from primary fuels through physical or chemical processing. They are often more convenient or efficient to use. Examples include coke,charcoal,and $LPG$.
Classification:
$(i)$ Wood and Petroleum are primary fuels.
$(ii)$ Coke and $LPG$ are secondary fuels.

(N/A) Dry wood is not considered a good domestic fuel for the following reasons:
$(i)$ Burning wood produces a large amount of smoke,which causes air pollution and respiratory problems.
$(ii)$ It leaves behind a significant amount of ash (residue) after combustion,which is difficult to dispose of and reduces its overall heating efficiency.

(N/A) Obtaining energy from nuclear fusion reactions is preferable to obtaining energy from nuclear fission reactions for the following reasons:
$(i)$ For a given mass of fuel,the energy released from nuclear fusion is significantly larger than the energy released from nuclear fission.
$(ii)$ Nuclear fission produces radioactive waste,which poses a major challenge for safe disposal and environmental protection. In contrast,nuclear fusion does not produce such hazardous radioactive waste,making it a cleaner energy source.

(N/A) nuclear fusion reaction is a process in which two or more lighter atomic nuclei combine to form a single,heavier nucleus,accompanied by the release of a significant amount of energy.
The conditions required for a nuclear fusion reaction to occur are:
$(i)$ The temperature of the fusing nuclei must be extremely high,typically around $10^{7} \, K$,to overcome the electrostatic repulsion between the positively charged nuclei.
$(ii)$ The nuclei must be accelerated to very high speeds,often using particle accelerators or by creating high-pressure environments,to ensure they collide with sufficient kinetic energy to fuse.

(C) The pollution caused by fossil fuels can be reduced by the following methods:
$(i)$ Increasing the efficiency of the combustion process: By ensuring complete combustion of fuel,the emission of unburnt carbon particles and carbon monoxide can be minimized.
$(ii)$ Using various techniques to reduce the escape of harmful gases and ashes: Technologies such as scrubbers,electrostatic precipitators,and catalytic converters can be used to trap harmful pollutants like sulfur dioxide,nitrogen oxides,and fly ash before they are released into the atmosphere.

(N/A) The general principle involved in generating nuclear energy is nuclear fission. In this process, a heavy nucleus, such as $Uranium-235$ or $Plutonium-239$, is bombarded with slow-moving neutrons, causing it to split into smaller, lighter nuclei while releasing a tremendous amount of energy.
One common fuel used in a nuclear reactor is $Uranium-235$ $(U-235)$.

(N/A) Ocean thermal energy refers to the energy available due to the temperature difference between the water at the surface of the ocean and the water at deeper levels.
Due to sunlight,the water at the surface of the sea gets heated up,while the water in the deeper regions remains relatively cold.
This temperature difference is utilized to generate electricity.
The warm surface water is used to boil a volatile liquid like ammonia.
The high-pressure vapours of the liquid are then used to run the turbine of a generator,which produces electricity.

(D) Biomass,such as wood,has been used as a fuel for centuries,but it is inefficient and produces a lot of smoke.
In recent times,it has been modified to function as a more efficient fuel in the following ways:
$1$. By converting wood into charcoal,which burns without flames,is comparatively smokeless,and has a higher heat generation efficiency.
$2$. By processing biomass (like cow dung and plant waste) in a biogas plant to produce biogas (a mixture of methane,carbon dioxide,hydrogen,and hydrogen sulphide),which is an excellent,clean,and efficient fuel.

(N/A) windmill consists of a large structure erected at a significant height on a rigid support. At the top,it features blades similar to a fan. To generate electricity,the rotational motion of the windmill is utilized to turn the turbine of an electric generator.
$(b)$ $A$ water-lifting pump is a classic example where the rotational motion of a windmill was historically used to lift water from wells for irrigation or domestic use.

(N/A) $(i)$ $(a)$ It is cost-effective as solar energy is free of cost.
$(b)$ It is an eco-friendly method that causes no pollution.
$(ii)$ The phenomenon responsible for obtaining high temperature in a solar cooker is the $Greenhouse$ $effect$.
$(iii)$ The motivation behind using a solar cooker is to promote the use of non-conventional and renewable sources of energy,as fossil fuels are limited and non-renewable.

(N/A) Hydroelectricity is produced by constructing high-rise dams to obstruct the flow of water.
As the water level rises behind the dam,the kinetic energy of the flowing water is converted into potential energy.
When this water is released from a high level,it is directed through pipes to a turbine.
The falling water strikes the blades of the turbine,causing it to rotate.
This mechanical energy from the rotating turbine is then used to drive a generator,which converts it into electrical energy.

(N/A) Geothermal energy is harnessed through the following steps:
$1$. Molten rocks from the deeper parts of the Earth's crust are pushed upwards and trapped in specific regions known as $hot \text{ } spots$.
$2$. Underground water that comes into contact with these $hot \text{ } spots$ gets heated and turns into high-pressure steam.
$3$. This steam is then routed through pipes to the surface, where it is used to rotate the turbines of an electric generator, thereby producing electricity.

(N/A) $1$. Environment friendly: Wind energy is a clean source of energy that does not produce harmful greenhouse gases or pollutants during operation.
$2$. No recurring expenditure: Once the wind turbine is installed,the source of energy (wind) is free,leading to no recurring fuel costs.
$3$. Renewable source: Wind is a natural,inexhaustible source of energy that will not run out over time.

(N/A) Biomass is the organic matter produced by plants or animals,which serves as a renewable source of energy.
The reaction that takes place in a biogas plant is an anaerobic decomposition (or fermentation) reaction.
Main constituents of biogas:
$(i)$ Methane $(CH_{4})$
(ii) Hydrogen $(H_{2})$
(iii) Hydrogen sulphide $(H_{2}S)$
(iv) Carbon dioxide $(CO_{2})$
Reasons for considering biogas an ideal domestic fuel:
$(i)$ Biogas burns without smoke,causing less pollution.
(ii) It leaves no residue like ash,unlike wood,charcoal,or coal.

(N/A) wind energy farm consists of a number of windmills erected over a large area such that the energy output of each mill in the farm is coupled together.
Steps involved in generating electricity:
$1$. The kinetic energy of the wind is used to rotate the blades of the windmills.
$2$. The rotatory motion of the windmill is used to turn the turbine of an electric generator.
$3$. The energy output of each individual windmill in the farm is coupled together to generate electricity on a commercial scale.

(N/A) Hydropower plants convert the potential energy of falling water into electrical energy.
$(b)$ Advantages of hydroelectricity over thermal electricity:
$(i)$ Hydropower plants use water to run the station,which involves no fuel cost,whereas thermal power plants require fossil fuels,which are costly.
$(ii)$ Hydropower plants do not cause pollution,whereas thermal power plants cause significant environmental pollution.

(N/A)

Energy from Biomass	Energy from Hydropower Plant
$(i)$ Biomass is a renewable and conventional source of energy.	$(i)$ Hydropower is also a renewable and conventional source of energy.
$(ii)$ Biomass can be utilized locally,reducing transportation costs.	$(ii)$ Hydropower requires large-scale infrastructure and transmission networks.
$(iii)$ Biomass utilization does not cause significant ecological imbalance or displacement of populations.	$(iii)$ Construction of large dams for hydropower often causes significant ecological imbalance and displacement of local populations.
$(iv)$ Biomass energy production is generally more decentralized and economical for rural areas.	$(iv)$ Hydropower plants involve high initial capital investment and are relatively costly to set up.

(N/A) $(i)$ $PE$ of water stored in the reservoir changes into $KE$ as it flows through the tunnel.
$(ii)$ $KE$ of the flowing water is converted into rotational $KE$ of the turbine.
$(iii)$ Rotational $KE$ of the turbine is transferred to the armature of the generator.
$(iv)$ Rotational $KE$ of the armature is converted into electrical energy due to electromagnetic induction as the coils rotate within a magnetic field.

(N/A) Advantages:
$(i)$ It is used to propel sailboats.
$(ii)$ It is used to drive windmills which further operate water-lifting pumps and flour mills.
$(iii)$ Aeroplanes use this energy for their upward and downward movements.
$(iv)$ It is used for flying engineless aeroplanes called gliders and for generating electricity.
$(v)$ It is a renewable source,free of cost,and does not cause any pollution.
Limitations:
$(i)$ Windmills produce less energy compared to other conventional forms of energy production.
$(ii)$ They are totally dependent on wind,which may not be available at all times or in all locations.
$(iii)$ Windmills are large,bulky,and inconvenient to install and maintain compared to other energy forms.

(N/A) Biogas is considered an ideal fuel for the following reasons:
$(i)$ It has a high calorific value.
$(ii)$ It burns without producing smoke.
$(iii)$ It has a moderate ignition temperature.
$(iv)$ It does not produce harmful residues or toxic gases.
$(v)$ It is cost-effective and easily accessible.
Due to these characteristics:
$(i)$ Biogas serves as an efficient energy source, thereby addressing the fuel crisis.
$(ii)$ Since it burns cleanly, it minimizes air pollution, thus solving environmental problems.
$(iii)$ The use of animal waste and organic matter in biogas plants prevents the contamination of water bodies and soil, further protecting the environment.

(N/A) Wood is a renewable source of energy. However,a tree usually takes more than $15$ years to mature. Thus,replenishment of wood takes a long time. Felling of trees on a large scale also causes depletion of forest leading to environmental imbalance. Also,the calorific value of wood is low and it causes significant air pollution. Therefore,the use of wood as fuel is not advisable.

(N/A) The following factors prevent the use of solar cell panels to meet all our domestic needs for electricity:
$(i)$ High cost of installation.
$(ii)$ Limited availability of special grade silicon required to manufacture solar cells.
$(iii)$ The technology required to obtain high-purity silicon is extremely expensive.
$(iv)$ High cost of materials,such as silver,used for interconnecting solar cells in a panel.
$(v)$ Lack of efficient and affordable systems to store the electrical energy generated by solar panels.

(N/A) The process of obtaining biogas involves the following steps:
$1$. $A$ slurry of animal dung (e.g.,cow dung) and water is prepared in a mixing tank.
$2$. This slurry is fed into a digester,which is a sealed,underground tank made of bricks.
$3$. Inside the digester,anaerobic microorganisms break down the complex organic compounds present in the biomass.
$4$. This process occurs in the absence of oxygen and produces gases like methane $(CH_4)$,carbon dioxide $(CO_2)$,hydrogen $(H_2)$,and hydrogen sulphide $(H_2S)$.
$5$. The resulting mixture,known as biogas,is collected and supplied to consumers through pipes.
Anaerobic decomposition is the process where microorganisms (anaerobic bacteria) decompose complex organic matter such as carbohydrates,proteins,and fats present in animal and plant wastes into simpler substances like methane gas,in the presence of water but in the complete absence of oxygen.

(N/A) The floating gas holder type biogas plant consists of a digester tank,an inlet pipe for the slurry (biomass and water mixture),a gas holder (floating drum),and an outlet pipe for the spent slurry. The gas outlet is located at the top of the floating gas holder,which allows the produced biogas to be collected and supplied for use. The diagram is as shown below:

(N/A) The three forms of energy from the oceans are:
$(i)$ Tidal energy
$(ii)$ Ocean wave energy
$(iii)$ Ocean thermal energy
Ocean Thermal Energy Conversion $(OTEC)$ power plants are facilities designed to harness the temperature difference between the warm surface water of the ocean and the cold water at deeper levels to generate electricity.
Operation:
$1$. In an $OTEC$ power plant,the warm surface water of the ocean is used to boil a volatile liquid like ammonia.
$2$. The high-pressure vapours of this liquid are then used to drive turbines,which in turn rotate generators to produce electricity.
$3$. The cold sea water from deeper levels is pumped up to condense the vapours back into a liquid,which is then recycled.
$4$. This system can operate continuously for $24$ hours a day.

(N/A) $(i)$ The four gases commonly present in biogas are Methane $(CH_4)$,Carbon dioxide $(CO_2)$,Nitrogen $(N_2)$,and Hydrogen $(H_2)$.
$(ii)$ Two advantages of using biogas over fossil fuels are:
$(a)$ Biogas is a renewable source of energy as it is produced from biomass,whereas fossil fuels are non-renewable and finite.
$(b)$ Biogas is a clean fuel that does not cause significant air pollution upon burning,whereas the combustion of fossil fuels releases harmful pollutants like sulfur and nitrogen oxides,causing severe air pollution.

(N/A) $(i)$ Renewable sources of energy can be replenished naturally over a short period and can be used repeatedly,e.g.,wind energy. On the other hand,non-renewable sources of energy cannot be replenished once consumed and get exhausted over time,e.g.,coal.
$(ii)$ The use of wood as a fuel is not advised because the natural replenishment of forests is an extremely slow process compared to the rate of consumption. Furthermore,wood has a low calorific value,its burning causes significant air pollution,and it produces large amounts of ash,which creates disposal problems.

(N/A) $(i)$ The solar constant is approximately $1.4 \, kW/m^2$.
$(ii)$ $A$ plane mirror is used in a box-type solar cooker to reflect sunlight into the box.
$(iii)$ Hydrogen is difficult to use as a source of energy because: $(i)$ it is highly combustible and burns with an explosion,and $(ii)$ it has a very low ignition temperature,making it dangerous to store and transport.
$(iv)$ $A$ concave reflector-type solar cooker can attain temperatures up to about $200^{\circ}C$.
$(v)$ Fossil fuels are classified as non-renewable because they take millions of years to form and cannot be replenished once they are consumed.