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Solutions of Sources of Energy- Lakhmir Singh Manjit Kaur VSAQ, SAQ, LAQ, HOTS and MCQ Pg No. 130 Class 10 Physics
Very Short Answer Type Questions-Pg-130
1. Name the product of petroleum that is used to drive heavy vehicles.
2. Give one example of a good domestic fuel.
→ LPG i.e. Liquefied petroleum fuel. LPG is prepared by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum.
3. Name any one hydrocarbon fraction obtained during the fractional distillation of petroleum which is used as a domestic fuel.
→ Kerosene is one of the hydrocarbon fraction obtained during the fractional distillation of petroleum and used as a domestic fuel. It is widely used as a fuel in industry and households.
4. What are the various fuels which are used to generate electricity in a thermal power plant?
→ Fuels that are used to generate electricity in a thermal power plant are Coal, oil and gas.
5. Name any four fractions obtained from petroleum which are used as fuels.
→ Various fractions obtained during the fractional distillation (refining) of petroleum (or crude oil). Few of them are:
Diesel, Petrol, Kerosene, Petroleum gas etc.
6. What is the composition of liquefied petroleum gas (LPG)?
→ Liquefied Petroleum Gas (LPG) is made up of a combination of propane, butane, and trace amounts of other chemicals, including pentane. Butane comprises slightly less than 70 percent of the gas. Propane comprises nearly 29 percent of the gas, leaving just over 1 percent for the trace components.
7. Which gaseous fuel is being used increasingly in transport vehicles like cars and buses these days?
8. Write the full form of: (i) LPG (ii) CNG.
→ (i) LPG stands for Liquefied Petroleum Gas. They are flammable mixtures of hydrocarbon gases used as fuel.
(ii) CNG stands for Compressed Natural Gas. It is methane stored at high pressure.
9.What is the main constituent of:
→ (i) The main constituent of petroleum gas is butane which is often abused as an inhalant.
(ii) The main constituent of natural gas is methane. It constitutes about 75% of the mixture.
10. Name the component which is found in natural gas as well as in biogas.
→ Methane is found in both natural gas and biogas. In biogas it is about 50-65% whereas in natural gas it is around 75%.
11. State two important uses of natural gas.
→ Uses of natural gas are:
i) Natural gas is a fossil fuel used as a source of energy for heating, cooking, and electricity generation.
ii) It is also used as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals.
12. State one important use of CNG these days.
→ CNG combustion produces fewer undesirable gases than other fuels. It is safer than other fuels in the event of a spill. Hence, CNG is mostly used as a fuel in transport vehicles these days.
13. Complete the following sentence:
Domestic gas cylinders like Indanecontain mainly ………………….
14. Explain why, natural gas is considered to be a good fuel.
→ Natural gas is primarily made of methane (the lightest hydrocarbon).It burns more cleanly than other fossil fuels, emitting lower levels of harmful emissions such as carbon monoxide, carbon dioxide and nitrous oxides. It produces less greenhouse gases than other fossil fuels do. Hence, Natural gas is considered to be a good fuel.
15. What is meant by conventional sources of energy? Write the names of two conventional sources of energy.
→ The conventional sources of energy are generally non-renewable sources of energy, which are being used since a long time. These sources of energy are being used extensively in such a way that their known reserves have been depleted to a great extent. Coal, oil and natural gas are a few examples of it.
16. Explain the principle of working of a thermal power plant. Draw a labeled diagram to illustrate your answer.
→ In a thermal power plant, the heat that is generated by combustion of coal is used to boil water to form steam. Then, the steam, being at high temperature and pressure, rotates the turbine and its shaft, which drives the generator to produce electricity.
17. What is the disadvantage of burning fossil fuels?
a)Fossil fuels have had a good run, but they’re on their last legs.
b)Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming.
c) Combustion of fossil fuels releases acidic gases.
d)The burning of fossil fuels produce smoke and leaves behind a lot of ash.
18. Write a short note on the pollution caused by burning fossils fuels.
→ Most fossil fuels are burned to turn into energy, and the gasses released into the air by burning, in turn causes air and water pollution. Gases released by the burning of fossil fuels include carbon monoxide, nitrogen oxides, sulfur oxides and hydrocarbons. In the air, these gases become a carcinogen, which can be inhaled and can also mix with falling rain to form acid rain.Also, burning of fossil fuels produces smoke and a lot of ash.
19. What are the various steps which can be taken to control (or reduce) pollution caused by burning fossil fuels?
→ We can reduce pollution by fossil fuels by following ways:
● We can reduce the consumptions of fossil fuels globally, by using less energy as an individual.
● By using more efficient machines that will emit less pollutant.
● By introducing techniques of treating the pollutant before emitting in the atmosphere.
● By using alternative safer, eco- friendly technologies.
20. If you could use any sources of energy for heating your food, which one would you use and why?
→ If I could use any sources of energy for heating my food, I would prefer LPG i.e. Liquefied Petroleum Gas because as an idle fuel it has a high calorific value and burns with smokeless flame.
21. Why is LPG considered a good fuel?
→ Liquefied Petroleum Gas is considered a good fuel because of the following reasons:
b) It is a very neat and clean domestic fuel. It burns with a smokeless flame and hence does not cause pollution.
c) It does not produce any poisonous gases on combustion.
d) LPG is easy to handle and convenient to store.
22. Why is LPG considered a better fuel than coal?
→ LPG is better than Coal in the following points:
a) It can be easily transported to our homes through pipelines.
b) It has a high calorific value.
c) It does not leave a solid residue and neither forms harmful gases.
d) It is easy to store.
e) It is readily available.
f) It has a low ignition point.
g) It burns at a moderate rate and its combustion is controllable using a knob.
23. Why is the leakage of LPG detected easily although it is odorless? State the steps to be taken in case its leakage is detected in the kitchen.
→ In order to detect the leakage, a foul smelling substance called ethyl mercaptane is added to the LPG. with that strong pungent smell, we can easily know if there is a leak.
In case of LPG leakage in the kitchen, following steps must be taken:
a) The door and windows should be opened to allow the gas to escape.
b) The source of gas leakage should be checked and then set right with the help of a gas mechanic.
Long Answer Type Questions-Pg-131
24A. What are fossils fuels? Give three examples of fossils fuels.
→ The fuels that are formed from the remains of dead plants and animals that lived millions of year ago are called fossil fuels. For e.g.: coal, petroleum, diesel, etc.
24B. Describe how fossil fuels were formed.
→ When the ancient plants and animals died, they decomposed and became buried under layers and layers of mud, rock, and sand. Eventually, hundreds and sometimes thousands of feet of earth covered them. In some areas, the decomposing materials were covered by ancient seas, then the seas dried up and receded. Hence, these materials away from the reach of oxygen, got converted into fossil fuels due to the chemical effects of pressure, heat and bacteria.
24C. Explain how, sun is considered to be the ultimate sources of fossil fuels.
→ The sun is the ultimate source of almost all kinds of energy on earth, either directly or indirectly. Fossil fuels are the transformed forms of plants and animals which once lived on the earth and grew capturing the energy of the sun. Biomass is a product of photosynthesis where the sun has the major role. Hydro-electricity depends upon the water cycle which again is dependent on solar radiation. Similarly, wind energy, tidal power, wave power all, in some way or other, and depend on the sun.
24D. Which fossil fuels were formed by the buried remains of large land plants?
→ Petroleum and natural gas are such fuels.
24E. Which fossil fuel was formed by the buried remains of large land plants?
Multiple Choice Questions (MCQs)-Pg-131
25. The main constituent of petroleum gas is:
→ Petroleum gas consist mainly of butane with a very small amount of ethane and propane.
26. The natural gas consist mainly of:
→ Typically if we see then natural gas consist 90% of methane.
27. Which of the following is not produced by the burning of fossils fuels?
→ Burning of fossil fuels release various gasses like sulphur oxide, carbon dioxide, carbon monoxide, etc.
28. The product of petroleum used to drive heavy vehicles like truck is:
→ Diesel fuel in general is any liquid fuel used in diesel engines, whose fuel ignition takes place, without any spark, as a result of compression of the inlet air mixture and then injection of fuel.
29. The aviation fuel which is used in the engines of jet aeroplanes is:
→ Kerosene, also known as paraffin, lamp oil and coal oil (an obsolete term), is a combustible hydrocarbon liquid which is derived from petroleum, widely used as a fuel in industry as well as households.
30. The ultimate sources of energy stored in fossil fuels is:
→ Since plants and animals’ existence depends on the sun directly or indirectly and fossil fuels are formed due to the remains of plants and animals hence, we can say that sun is the ultimate source of energy stored in fossil fuels.
31. Which of the following is not a fossil sources of energy?
B. cow- dung cakes
→ It is the excretion of a cow and not the remains of dead and decaying plants and animals.
32. The fuel which is not used at thermal power plants is:
→ It is a nuclear fuel used at nuclear power plants.
33. LPG consists mainly of:
→ Liquified Petroleum Gas contains 60% of butane.
34. Coke is more valuable when used
A. as a fuel for industrial
B. as an oxidizing agent
C. as a reducing agent
D. as a fuel in domestic ovens
→ This is because it is a non-metal and it combines with oxygen and forms its gaseous non-metallic oxides.
35. Coal is more valuable when used:
→ As charcoal do not produces smoke while burning and has a low ignition temperature and high calorific value.
36. One of the following does not contribute to acid rain. That is:
→ Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH).
Questions Based on High Order Thinking Skills (HOTS)-Pg-132
37. Fossil fuels are energy rich compounds of an element X which were originally made by the plants with the help of sun’s energy.
(a) Name the element X
(b) Name another element which is usually found in combination with X in fossil fuels.
→ (a) X is carbon
(b) Hydrogen is another element which is usually found in combination with carbon in Fossil fuels.
38. The energy in petrol originally came from the Sun. Explain how it got into petrol.
→ Fossil fuels are obtained from remains of animals and plants under the earth over a period of millions of years these existed and grew due to sun's energy thus the ultimate source of fossil fuels can be considered to be the sun's energy.
39. A substance X is added to LPG cylinders while filling so as to make the detection of leakage of LPG from the cylinders easy.
(a) Name the substance X
(b) How does substance X make the detection of leakage of LPG easy?
→ (a) X is Ethyl mercaptan
(b) Ethyl mercaptan has a foul smell which can be detected easily at the time of leakage of LPG.
40. 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.
(a) Name the device X
(b) How does this device help in controlling air pollution ?
→ (a) Catalyltic converter- A catalytic converter is an emissions control device that converts toxic gases and pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction)
(b) It helps in controlling air pollution by changing poisonous carbon monoxide into non-poisonous carbon dioxide and also converts harmful nitrogen oxides into harmless nitrogen gas.
Very Short Answer Type Questions-Pg-140
1. A hydro-power plant converts one from of energy into another. Name the two forms of energy.
→ A hydroelectric power station converts the kinetic energy of flowing or falling water into electrical energy that can be used in homes and businesses.
2. What type of energy is possessed by flowing water?
→ Kinetic energy is possessed by flowing water.
3. Flowing water can rotate a turbine. Which type of energy is used up by the turbine?
→ Kinetic energy of flowing water is used up by the turbine and later it it is converted into electrical energy.
4. Name the original source of wind energy.
→ Sun is the original source of wind energy. The sun’s radiation warms different parts of the earth at different rates. The result of this uneven heating is atmospheric change. Hot air rises, leaving decreased atmospheric pressure near the earth’s surface, and cool air is drawn in to replace it. The result of this air exchange is wind.
5. What should be the minimum wind speed for the satisfactory working of a wind- powered electric generator?
→ 15km/hr should be the minimum wind speed for the satisfactory working of a wind- powered electric generator.
6. Write one use of wind energy
(a) In the past
→ a) In the past wind energy was used in the flour mills.
b) In the present days wind energy is mainly used for generating the electricity through wind-powered generators.
7. Why is the copper tube of a solar water heater painted black from outside?
→ The copper tube is painted black to improve their ability to absorb thermal energy. Black reflects the least amount of radiation (about 3%) of any color, and therefore absorbs almost all the radiation energy to which it is exposed.
8. What type of reactions occurring inside the sun produces solar energy?
→ Nuclear fusion reactions occur inside sun that produces solar energy. This reaction, converts hydrogen atoms into helium.
9. Name some of the solar energy devices.
→ Solar panel, Solar charge controller, Solar inverter, Solar micro-inverter, Solar cable, Photovoltaic mounting system, etc are some of the solar energy devices.
10. What type of reflector is used in a box-type solar cooker?
→ Plane mirror with high specular reflectivity is used as a reflector in box-type solar cooker to concentrate light from the sun on to a small cooking area.
11. What is the range of temperature which can be achieved in a box-type solarcooker in two to three hours?
→ The range of temperature which can be achieved in a box-type solarcooker in two to three hours is from 100°C to 140°C.
12. Name the devices which converts sunlight into electricity.
→ Solar cells convert sunlight into electricity. It is a form of photoelectric cell.
13. How much solar energy will be received by 1 m2 area in one hour if the solar constant be 1.4 kW/m2?
→ From the solar constant we deduce that
1.4 kW of power is incident upon every 1m2 of area.
i.e the total energy incident in 1 hr over an area of 1 m2 will be = 1.4 kW x 1 hr
(Since P=E/t or E=P x t)
Hence, energy = 1.4 kWh
Solar energy received by 1 m2 area in one hour (or 3600 s) = 1.4 x 3600 = 5040 kJ.
14. Fill in the following blanks with suitable words :
A solar cell converts …………………. energy into …………………. energy.
→ Solar energy into electrical energy.
Short Answer Type Questions-Pg-140
15A. What is the difference between a thermal power plant and hydro power plant?
→ The main difference between Thermal Power plant and Hydro Power plant are: The thermal power is produced by burning coal, petroleum or natural gas in thermal generator whereas the Hydro-electricity or Hydro power is derived from the force of running water by means of dynamo driven by hydro-turbine.
15B. Which of the two causes serious air pollution and how?
→ Among them, thermal power plant causes serious air pollution because it emits harmful gases like nitrogen oxide, sulphur dioxide and fly-ash into the air.
16. Compare the sun and the fossil fuels as the sources of energy.
→ Coal and petroleum are fossil fuels they are obtained from deep under Earth’s crust. They are directly available to human beings for use. Therefore fossil fuels are the direct source of energy. But these are limited in amount also they are non-renewable.
Sun is also a direct source of energy. But it is renewable source of energy. The Sun has been shining for several years and will continue billions of years more. Solar energy is available free of cost to all in unlimited amount.
17. What kind of mirror, concave, convex or plane, would be best suitable for use in a solar cooker? why?
→ A concave mirror would be best suited for use in a solar cooker. When a concave mirror reflector is attached to a solar cooker, it converges a large amount of Sun's heat radiations at its focus due to which a high temperature is produced at the focus area.
18A. Name that part of a box-type solar cooker which allows the sun’s rays to enter the box but does not allow inside heat to go out.
→ The box is covered by a thick transparent sheet of glass. When the box is placed in the sunlight, the glass cover allows the infrared rays present in sunlight to pass into the box. Then these rays are absorbed by black surface of the box and the box becomes hot. But, after sometime when the black surface becomes hot it starts radiating out heat in the form of infrared rays. But, the glass sheet cover placed over the box does not allow the heat radiated by the black surface to go out from the box. In this way, the glass cover enables the cooker to entrap the heat inside it.
18B. Explain why, a plane mirror reflector is used in a box-type solar cooker.
→ Usually, a plane mirror reflector is attached on the top of the box. This is because the plane mirror reflector increases the efficiency of solar cooker by reflecting more and more sunlight inside the box.
19. What are the advantages and disadvantage of using a solar cooker?
→ Advantages of using a solar cooker are:
a) There is no cost of fuel.
b) It is environment friendly and there is no residue like ash etc.
c) Cooking is hygienic and nutritious.
Disadvantages of using a solar cooker are:
a) The cooking is slow.
b) It cannot be used at all times.
c) A solar cooker can perform only limited functions.
d) Solar cookers have limited utility at the places where sunlight is less as in polar regions or where there are too much rains.
20A. What is a solar cell? Draw the labeled diagram of a solar cell.
→ A solar cell or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
20B. Name the semi-conductor material which is usually used for making solar cells.
→ Silicon is usually used for making solar cells.
20C. Write the uses of solar cells.
→ Uses of solar cells are:
● Solar cells are very useful in powering space vehicles such as satellites and telescopes (e.g. Hubble).
● solar cells see wide use as an off-grid energy source.
● To provide electricity to remote areas where normal electricity transmission lines do not exist.
● To provide electricity to light houses.
21. State the advantage and disadvantage of using solar cells.
→ Advantages of using solar cells are:
●Electricity produced by solar cells is clean and silent.
●Photovoltaic systems are quiet and visually unobtrusive.
●Small-scale solar plants can take advantage of unused space on rooftops of existing buildings.
●Solar energy is a locally available renewable resource.
Disadvantage of using solar cells are:
●Some toxic chemicals, like cadmium and arsenic, are used in the PV production process.
●Solar energy is somewhat more expensive to produce.
●Solar power is a variable energy source, with energy production dependent on the sun.
22. What is a solar cell panel? For what purpose is it used? State its two main advantages.
→ Solar panels are devices that convert light into electricity. They are called "solar" panels because most of the time, the most powerful source of light available is the Sun, called Sol by astronomers. Two main advantages of using solar panels are:
a) It provides much more electric power than a single solar cell.
b) It is used to provide electricity in remote and inaccessible rural areas.
23A. What is solar constant? What is the value of solar constant?
→ Solar constant is the rate at which energy reaches the earth's surface from the sun, usually taken to be 1,388 watts per square metre.
Its value is 1.4kJ/s/m2.
23B. If the energy received by 5 m2 area in 10 minutes is 4200 kJ, calculate the value of solar constant.
→ Area, A=5 m2
Solar constant =E/(A x t)
24. How has the traditional use of energy of flowing water been modified for our convenience?
→ Traditionally, waterfalls were used as a source of potential energy in which water is allowed to fall on the blades of the turbine where the rotatory motion of the blades of the turbine is converted into electrical energy. But waterfalls are few in number therefore water dams have been constructed. Nowadays, hydro-electric power stations are used in order to harness potential energy of stored water.
25. How has the traditional use of wind energy been modified for our convenience?
→ Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting or drawing water from a well. But now a day’s windmills are used to generate electricity. In windmills the rotatory motion of the blades turns the blades of turbine to generate electricity.
Long Answer Type Questions-Pg-141
26A. What is hydro electricity? Explain the basic principle of generation of hydroelectricity with the help of a labeled diagram.
→ As the name indicates hydroelectricity is the electricity that is produced through water. Conservation of energy is the basic principle that is used for the generation of hydroelectricity which is explained in the following diagram:
26B. State two advantage of producing hydroelectricity.
→ The two advantages of using hydroelectricity are:
i) Hydropower is fueled by water, so it's a clean fuel source, meaning it won't pollute the air like power plants that burn fossil fuels.
ii) Hydroelectric power is a domestic source of energy, allowing each state to produce their own energy without being reliant on international fuel sources.
26C. State two disadvantage of producing hydroelectricity.
i) Hydroelectricity plants are very expensive.
ii) The building of dams for hydroelectric power can also cause a lot of water access problems.
27A. With the help of a labeled diagram, explain the construction and working of a solar cooker.
→ Solar cookers vary in design, but many feature a chamber lined with reflective surfaces, such as aluminum foil and a clear, plastic or glass window, through which the sunlight enters. When sunlight passes through plastic or glass, its spectrum shifts, and much of the ultraviolet radiation is filtered out. However, this filtered light transforms into heat, which raises the temperature inside the solar cooker.
27B. Why is the solar cooker box painted black from inside?
→ As we know that dark colors are a good conductor of heat. Therefore to absorb a large amount of heat solar cookers are painted black.
27C. Why is the solar cooker box covered with a glass sheet?
→ When sunlight falls over the solar cooker top, the sun rays pass through the glass sheet cover and get absorbed inside the cooker box.
This glass sheet covers does not allow the solar energy to flow out in the form of radiant heat. Thus it traps more and more heat rays of the sun thereby producing greenhouse effect. That is why glass lid is used in the solar cooker.
28A. What is wind? What type of energy is possessed by wind?
→ Wind is moving air and is caused by differences in air pressure within our atmosphere. Wind possesses a form of energy referred to as kinetic energy. Kinetic energy is energy of motion i.e. energy that a body possesses because it is in motion.
28B. Explain how, wind energy can be used to generate electricity. Illustrate your answer with the help of a labeled diagram.
→ Wind turbines convert the kinetic energy in the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity.
28C. State two advantage of using wind energy for generating electricity.
→ Advantages of using wind energy for generating electricity are:
(i)Wind energy itself is both renewable and sustainable. The wind will never run out.
(ii)Wind turbines have a relatively small land footprint.
28D. Mention two limitations of wind energy for generating electricity.
→ Limitations of wind energy are
(i) Wind energy has a similar drawback to solar energy in that it is not a constant energy source.
(ii) Although costs are reducing over time, the installation of a wind turbine is considered expensive.
Multiple Choice Questions (MCQs)-Pg-141
29. A solar water heater cannot be used to get hot water on:
A. a sunny day
B. a cloud day
C. a hot day
D. a windy day
→ At it won't get the sufficient sunlight to create greenhouse effect.
30. At a hydro power plant:
A. kinetic energy possessed by stored water is converted into electrical energy
B. electricity is extracted from water
C. water is converted into steam to turn turbines and produces electricity.
D. potential energy possessed by stored water is converted into electricity.
→ A hydro power plant is a complex of installations and equipment that is used to convert the energy of a stream of water into electrical energy.
31. The part of box-type solar cooker which is responsible for producing greenhouse effect is:
A. plane mirror reflector
B. black coating inside the box
C. glass sheet cover
D. utensils placed in the cooker box
→ As it traps the absorbed radiations inside traping more and more heat.
32. Solar cells are made of:
→ Because in semiconductors, the energy band gap is quite less. The photons can easily eject the electrons out of it provided the energy of the electrons is more than the threshold energy required.
33. The value of solar constant is
→ The solar constant, is the conventional name for the mean solar electromagnetic radiation (the solar irradiance) per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) from the Sun (roughly the mean distance from the Sun to the Earth).
34. The radiations present in sunlight which make a solar cooker work are
A. visible light rays
→ Infrared radiation, or simply infrared or IR, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore invisible.
35. In order to make an efficient solar cooker, the cover box should be made of :
A. transparent plastic sheet
B. shining alluminium sheet
C. butter paper sheet
D. transparent glass sheet
→ As it do not allows the absorbed radiations to pass out hence, trapping out more and more heat.
36. The minimum speed of wind necessary for the satisfactory working of a wind generator to produce electricity is about :
→ A wind turbine is a device that converts the wind's kinetic energy into electrical power.
37. If the solar constant is 1.4 kW/m2, then the solar energy received by 1 m2 area in one hour is :
→ From the solar constant we deduce that
1.4 kW of power is incident upon every 1m2 of area.
i.e. the total energy incident in 1 hr over an area of 1 m2 will be
= 1.4 kW x 1 hr
(Since P=E/t or E=P x t)
Hence, energy = 1.4 kWh
Converting into Kj we get 5040 Kj).
38. A solar cooker may not cook food if :
A. the solar cooker is not placed in the shade
B. the glass sheet cover of solar cooker is not closed
C. a convex mirror reflector is not used
D. the food containers of insulating material are not used
→ Glass sheet covers does not allow the solar energy to flow out in the form of radiant heat. Thus it traps more and more heat rays of the sun thereby producing green house effect. That is why glass lid are closed in the solar cooker in order to trap more and more heat.
Questions Based on High Order Thinking Skills (HOTS)-Pg-142
39. A large coal-fired power station producers 2000 MW of electrical energy. A wind turbine with 33 m blades can produces 300 kW.
(a) How many turbines would be needed to replace the power station?
(b) Why, in actual practice, this number of turbines could not replace the coal-fired power station?
→ (a) Electrical energy produced by coal-fired plant,
Electrical energy produced by wind turbine
No. of wind turbine required,
= 2000x106/300x103 = 6666.6
Hence, 6667 wind turbines would be needed to replace the power station.
(b) In actual practice, this no. of wind turbines could not replace the coal-fired power plant because the efficiency of wind turbines keeps changing due to changes in wind speed but the efficiency of steam turbines used in coal-fired power stations remains the same.
40. In a solar water heater, why is the storage tank placed at a higher level than the solar panel containing coils?
→ In a solar water heater, the storage tank placed at a higher level than the solar panel containing coils because hot water, being lighter and less denser, rises to the top.
41. In many applications, solar cells are connected to rechargeable batteries. Why is this so?
→ The electricity that is produced by the solar cells during the day time is stored in the rechargeable batteries so that the produced electricity can be used later on, for instance, at night.
42A. 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.
→ At first, with the help of solar cells, solar energy is converted into electrical energy. Then, while charging the batteries this electrical energy gets converted into chemical energy.
Later, while using the batteries, chemical energy again gets converted into the electrical energy and then the electric motor converts electrical energy into kinetic energy.
42B. What difference would you expect in the charging of car battries
(i) in bright sunlight
(ii) on a cloudy day
→ (i) Due to the large amount of solar energy, batteries of the car gets charged quickly.
(ii) As on a cloudy day less amount of sunlight is present therefore batteries charge up very slowly.