Ques 1: What are the drawbacks of wind energy?
Ans: The power which is generated using wind energy is not much efficient and also we cant get the power generation all the times.
Ques 2: How is tidal energy harnessed?
Ans: High tides of sea, which can be used to generate power by using the turbine. A turbine converts mechanical energy into electrical energy.
Ques 3: Why is charcoal a better fuel than wood?
Ans: Charcoal is a better fuel than wood, because it has high thermal capacity than wood.
Ques 4: How is biogas prepared?
Ans: When wood is compressed for a number of years inside the earth, it becomes charcoal. By using the charcoal, we can produce the biogas. Methane is the known biogas.
Ques 5: Explain the function of turbine.
Ans: Turbine is one which converts the mechanical energy into electrical energy. Hydroelectric power is generated using turbines which converts air pressure into electrical energy using rotation of turbines and also flow of water through turbines converts mechanical energy into electrical energy.
Ques 6: Give some examples for renewable and non-renewable sources?
Ans: Solar energy, wind energy are the examples of renewable sources. Coal, petroleum, fuel are the examples of non-renewable sources.
Ques 7: Which is the known biogas?
Ans: Methane is the known biogas.
Ques 8: Heat produced on burning 5gm of a fuel raises the temperature of 1 kg of H2O from 20oC – 60oC. If the specific heat of H2O is 4.2J/goC, calculate the calorific value of the fuel?
Ans: Formula: mst = 5 gm x 4.2 x 40 = 840.
Ques 9: Explain greenhouse effect.
Ans: The phenomenon whereby the earth’s atmosphere traps solar radiation, caused by the presence in the atmosphere of gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but absorb heat radiated back from the earth’s surface.
Ques 10: Why does the interior of a car parked in the sun become hot?
Ans: The solar radiation which is absorbed by the car is the basis for the green house effect.
Ques 11: What is solar constant?
Ans: The Solar Radiation that falls on an area above the atmosphere at a vertical angle: s = 1.37 kW / m². In space, solar radiation is practically constant; on earth it varies with the time of day and year as well as with the latitude and weather. The maximum value on earth is between 0.8 and 1.0 kW / m². In Germany, the average annual amount of insolation varies between 950 and 1100 kWh / m², depending on the region.
Ques 12: What radiations are converted to electricity in a solar cell? What are they used?
Ans: Solar radiations are converted into electricity in solar cell which is used in traffic signal lights, etc.
Ques 13: Name any two renewable sources of energy.
Ans: Solar energy and wind energy.
Ques 14: Explain about calorific value of fuel.
Ans: Heat energy is measured in units of joules or calories (1calorie = 4.18 joules). The heat generated by fuels when they burn in joules or calories measures quality of fuels. All fuels do not burn efficiently. Thus there are fuels that produce more heat than the others are. This can be distinguished in terms of number of joules or calories that they generate on burning.
Ques 15: Define ignition temp. Which has lower ignition temperature, kerosene or LPG. Why?
Ans: When any substance tends to burn for a particular temperature it is called the ignition temperature for that particular substance.
Ques 16: Explain about solar collector.
Ans: Solar collector is a form of collector which collects solar energy and transforms the solar energy to the form which can be utilized according to the system.
Ques 17: What are the characteristics of source of energy?
Ans: Characteristics are generally classified in to renewable sources of energy and non-renewable sources of energy, which is used in heating, producing power, etc.
Que 18: How is electricity produced from thermal power plants?
Ans: In thermal power plants, heat is converted into steam energy which runs the turbine to get electrical energy.
Ques 19: Give the peculiar property of glass sheet?
Ans: A glass sheet transmits solar radiation into it as a semiconductor.
Ques 20: What are the important factors/parts in constructing a solar cooker? Give its importance.
Ans: Black coated sheets, glass plates, vessel, etc.
Ques 21: Give one main difference between solar cooker and solar concentrator.
Ans: In solar cooker, solar radiation spreads at all the points, whereas in solar concentrator it is concentrated at a particular point.
Ques 22: Explain the construction of a solar cell. Give the uses of solar cell.
Ans: Solar cell consists of a black plate, which absorbs the solar radiation and converts this solar radiation in to electrical energy by the process of photoelectric effect. It is used in traffic signals, etc.
Ques 23: How is harnessing hydroelectric energy done on a small scale?
Ans: By using the flow of water in rivers and dams, hydroelectricity is demonstrated and power is generated.
Ques 24: Explain about hydroelectricity.
Ans: It is the conversion of flow of water in to electric power. The basic process is electromagnetic induction, which converts mechanical energy into electrical energy.
Ques 25: How is biogas energy better than any energy?
Ans: Biogas energy is better than any other energy, because it is not harmful at any cause and it is pollution free.
Ques 26: Why are hydrogen and alcohol not commercial fuel?
Ans: When alcohol is used as a fuel, then the byproduct is carbon dioxide and carbon monoxide. This is the reason that hydrogen and alcohol are not commercial fuel.
Ques 27: Explain wind energy.
Ans: Wind energy is the conversion of air pressure into electric power. The high pressure wind runs the wind mill, which in turn produces electric power.
Ques 28: What are the qualities in choosing a good fuel?
Ans: Must be highly efficient, low in cost and durable.
Ques 29: What are the limitations of harnessing wind energy? Where is the largest wind energy farm in India?
Ans: Windmill gives high efficiency only in wind seasons. Wind energy is the conversion of air pressure into electric power. The high-pressure wind runs the windmill, which in turn produces electric power. We have the wind mills in northern part of our country which produces high power.
Ques 30: Draw a neat diagram of the box type solar cooker. Label it and explain the function of each part.
Ans: A solar cooker is like a hot box, in which we can cook our food without any cooking gas or kerosene, electricity, coal or wood. We do not need to spend even a single paisa on fuel. This cooker works with the solar energy, which is available free. In a solar cooker we can boil, bake and roast, and in a cooker for domestic use, we can cook food for four to five persons. Bigger size solar cookers are also available for cooking food upto 15 persons.
Insulating Box
A solar cooker consists of a well-insulated box for storing energy. To increase the absorption of solar radiation, the inside of the box is painted back.
Glass Lid
The insulated box has a glazing glass surface for collecting energy. The solar cooker absorbs the Sun’s radiant energy through this glass lid.
Reflector
The insulated box has a reflector, which is an ordinary mirror used to reflect sunlight into the box. This reflector helps to track the movement of the sun, focusing sunlight and therefore concentrating the heat energy inside the box.
Black Pots
Solar absorption is also increased by using dark-coloured pots for cooking. The vessels that are painted in black are placed inside the box with the food to be cooked.
Ques 31: Why is the sun very hot than any other hot body and how does it continously emit solar energy? Justify.
Ans: Due to nuclear fusion, there is a continuous emission of solar energy.
Ques 32: Give the purpose of mirror and glass sheet in solar cooker.
Ans: In solar cooker glass sheet acts as a transparent medium which allows light into the medium. Mirror reflects the light which emerges from the cooker.
Ques 33: Why are solar cells not used effectively?
Ans: High expensive, not re-usable. Hence it is not used effectively.
Ques 34: Give the limitations in using commercially wood as fuel, over windmills.
Ans: Basic commercial fuel used is wood, because of its abundance in existence. Another fact is it is non-renewable but windmill energy is a renewable source of energy.
Ques 35: A student constructed a box type solar cooker. He found that it is not working efficiently. What could this be due to? Give any four possible mistakes that he could have made?
Ans: The transparency of the glass plate must be checked.
The reflectance of the mirror is to be checked.
The black coating must be coated effectively.
The solar cooker must be placed in a way such that it faces the sun’s radiation.
Ques 36: What are the advantages of using solar water heater? Draw a labeled schematic diagram for a solar water heater.
Ans: A Solar Water Heater (SWH) is a device that uses solar energy to heat water. Solar Water Heater have several advantages over conventional water heating systems. For consumers, they save electrical energy, save interior space (because they are usually located on rooftops,) and eliminate the risk of accidents in bathrooms due to electrical water heating equipment, They require little or no care and attention while providing hot water for about 300 days in a year in most parts of India. For society at large, they reduce the need for fossil fuels for electrical generation and for fuels such as firewood, coal, furnace oil, etc, that are used in domestic, commercial and industrial boilers. Thereby, they also reduce degradation of the environment
Solar water heater
Ques 37: Define solar constant.
Ans: The amount of solar energy form the sun which incident on the earth per square metre is called solar constant.
Ques 38: What is the main basic cause for winds to blow? Compare wind power and power of water flow in respect of generating mechanical and electrical energies.
Ans: The main basic cause for the winds to blow is the difference in temperature of the atmosphere, which makes the air to get high dense and low dense and in turn flow from one part to other. When comparing wind power and hydroelectricity, it seems that hydroelectricity is better when compared with wind energy.
Ques 39: Write two limitations of wind mill.
Ans: An estimated 1% to 3% of energy from the Sun that hits the earth is converted into wind energy. This is about 50 to 100 times more energy than is converted into biomass by all the plants on Earth through photosynthesis. Most of this wind energy can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth’s surface and atmosphere.
The origin of wind is simple. The Earth is unevenly heated by the sun resulting in the poles receiving less energy from the sun than the equator does. Also the dry land heats up (and cools down) more quickly than the seas do. The differential heating powers a global atmospheric convection system reaching from the Earth’s surface to the stratosphere which acts as a virtual ceiling.
Ques 40: Explain wind power, the principle behind wind mill and its uses.
Ans: Wind power is the conversion of wind energy into more useful forms, usually electricity using wind turbines. In 2005, worldwide capacity of wind-powered generators was 58,982 megawatts; although it currently produces less than 1% of world-wide electricity use, it accounts for approximately 25% of electricity use in Denmark, 9% in Spain, and 6% in Germany. Globally, wind power generation more than quadrupled between 1999 and 2005.
Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. In windmills (a much older technology) wind energy is used to turn mechanical machinery to do physical work, like crushing grain or pumping water.
Wind power is used in large scale wind farms for national electrical grids as well as in small individual turbines for providing electricity to rural residences or grid-isolated locations. Wind energy is ample, renewable, widely distributed, clean, and mitigates the greenhouse effect if used to replace fossil-fuel-derived electricity.
Ques 41: (a) What is a solar water heater?
(b) Mention one advantage and one disadvantage of harnessing solar energy.
Ans: (a) A Solar Water Heater (SWH) is a device that uses solar energy to heat water.
(b) Solar Water Heater have several advantages over conventional water heating systems. For consumers, they save electrical energy, save interior space (because they are usually located on rooftops) and eliminate the risk of accidents in bathrooms due to electrical water heating equipment, They require little or no care and attention while providing hot water for about 300 days in a year in most parts of India. For society at large, they reduce the need for fossil fuels for electrical generation and for fuels such as firewood, coal, furnace oil, etc, that are used in domestic, commercial and industrial boilers. Thereby, they also reduce degradation of the environment.
Ques 42: Draw the two common designs of solar cookers.
Ans: Box type solar heater and Spherical type solar heater.
Ques 43: What is the meaning for gobar?
Ans: Gobar means animal dung in Hindi.
