Source Of Energy

Solar energy being a very good and renewable source of energy has some disadvantages also. Solar cells and their installation requires a lot of money and therefore not many people can afford it. Also, they are weather dependent and cannot be used in rainy season or at the time of the year when sun is not visible.

A windmill is a device (mill ) that converts wind energy into electricity by using the blades of the windmill. The minimum velocity required by a windmill to obtain useful energy is 15 kilometres per hour.

The glass plate does not allow the heat to escape. This phenomenon is used in solar cookers as the solar cooker box is covered with a plane glass plate so as to capture more and more rays of the sun and allow maximum heating of the food placed in the box

Solar cells are the renewable source of energy which converts the solar energy (energy from the sun) into electricity. A few areas in which solar cells are used are as follows:

• Solar cells are used in traffic lights and street lights.

• Nowadays solar panels are also used in trains like metros.

• Food can be cooked using solar cookers.

• Some calculators also have solar cells embedded in them.

By classifying sources of energy as renewable and non-renewable :

• we can have a knowledge of how many sources are left and the proper ways they can be used so that we can pass them to our future generations.

• we can look for different alternates of the fast depleting non-renewable resources of energy.

(a) CNG-compressed natural gas. It is a type of natural gas which is a non- renewable source of energy as it takes thousands of years to get replenished. Thus CNG is a non-renewable source while hydrogen is a renewable source.

(b) Hydrogen is a much cleaner fuel than CNG because-

•there is no hydrocarbon emission from hydrogen while CNG produces a lot of hydrocarbon emission which can cause pollution.

India is a country which is surrounded by water on three sides. This water is now used to generate electricity. thus hydropower plants are a good source of generating energy in India nowadays.

Generation of electric energy in hydropower plant:-

Electricity production in a hydropower plant works on the principle that- energy always remains conserve and one form of energy can be converted into other.

Water from a great height is poured on a turbine with very great speed. This is done to convert the potential energy of water into its kinetic energy. When this water falls on turbine, it moves with very high speed thus converting this kinetic energy of water into electric energy.

Koyna Hydroelectric Project is the largest hydroelectric power plant in Maharashtra state of India.

there can be some basic mistakes which can be done by the student. Once the following mistakes are corrected, his/her solar cooker will start working efficiently-

1) he/she might not have painted the cooker black. Black color is the best absorber of heat, thus painting it black will give better results.

2) he/she might not have covered the solar cooker with a glass cover. This glass cover traps the heat inside the cooker thus increasing the temperature.

3) while constructing a solar cooker one must place spherical reflectors inside the cooker so that they can converge the light at specific point thus giving a better result.

4) the sides of solar cooker must be covered with some thermally insulating layer to reduce the heat loss.

the three forms in which energy from oceans is made available for use are-

1) wave energy

2) tidal energy

3) thermal energy

OTEC- ocean thermal energy conversion plant.

Water present at the surface of sea is continuously being heated due to sunlight but, the water present in the deep sea level is quite cold because sunlight is unable to penetrate deep into the water. So this difference in the different levels of water in the sea can be utilised efficiently to create electricity. It is done in OTEC i.e. ocean thermal energy conversion plants.

Biogas plant has a dome-shaped digestor in which cow dung is kept. It is completely isolated and thus does not have oxygen in them. In this anaerobic conditions, methanogens (methane producing bacteria) perform their function & produces methane (CH₄) by digesting the cow dung. Along with methane, carbon-dioxide (CO₂), hydrogen sulphide (H₂S) is also produced. These gases so produced is recovered from the gas outlet while the remaining slurry can be used as fertiliser.

two advantage of using animal dung for making biogas over using it as a fuel in the form of dried dung cakes are:-

1) biogas is a very clean fuel i.e. there is no hydrocarbon emission while using biogas but at the same time this cow dung is very polluting and can even cause various lungs related problems.

2) the remains of biogas i.e. the cow dung slurry can be used as a fertiliser so there will be no waste production while using biogas. But using dry dung cakes produces ashes which further creates a problem of its disposal.

Resources which can be used repeatedly over a long period of time without its shortage because they are constantly being replenished by nature are called as renewable resources, while those resources which are not are non-renewable. Among all the given options, wood is a renewable energy resource.

Sun is the ultimate source of energy for our earth. Energy in Sun is due to continuous fusion of H atoms to form He nuclei. Out of the total sun's energy, its 47% energy is received by earth.

plant is different from coal, petroleum & lignite. All these are fossil fuels, while plant is not.

Gobar gas is a non-conventional source of energy while all other are conventional sources. Coke, bitumen & anthracite have carbon content in them while gobar gas majorly contains methane. Moreover, gobar gas is a clearer fuel then rest of the given options.

Resources which can be used repeatedly over a long period of time without its shortage because they are constantly being replenished by nature are called as renewable resources, while those resources which are not are non-renewable. Coal, uranium & natural gas are non-renewable resources as they take thousands of years to get replenished. So the correct answer will be geothermal power which utilises the thermal energy stored in earth's crust.

VIBGYOR is the visible range of light starting from violet and ending to red colored light. Among all these violet light has the shortest wavelength & red light has the longest wavelength.

for red light :- 0.7 micron

for violet light:- 0.4 micron

sun is the ultimate source of energy for earth. The energy of sun is produced by continuous fusion of Hydrogen nuclei to form Helium nucleus. Thus, nuclear fuel in sun is HYDROGEN.

the kinetic energy of wind is utilised to generate electricity. In this, the wind energy is used to move the turbine of windmill at high speed which generates electricity. So the minimum speed required to move the fans of windmill is 15km/hr.

Water present at the surface of sea is continuously being heated due to sunlight but, the water present in the deep sea level is quite cold because sunlight is unable to penetrate deep into the water. So this difference in the different levels of water in the sea can be utilised efficiently to create electricity. A plant where electricity is created from this source is called as OTEC- ocean thermal energy conversion plant. The minimum temperature difference required for an OTEC to function is 20^oc.

calorific value is the amount of energy produced when combustion of 1 kg of a substance is done. So the calorific value of wood is 17kJ.

destructive distillation is a process in which a solid is heated in a completely closed container & all it fumes which contains various volatile substances are collected. So destructive distillation of wood does not show any sign of coal. Thus the answer is option (b).

calorific value is the amount of energy produced when combustion of 1 kg of a substance is done. So the energy liberated in charcoal combustion is 33 kJ.

destructive distillation is a process in which a solid is heated in a completely closed container & all it fumes which contains various volatile substances are collected. So, when destructive distillation of wood is performed & its volatile constituents are studied, 0.25 kg of charcoal was found.

fossils are remains of dead plants, animals & other organisms. These fossils are a great source of energy & thus called as fossil fuels.

Among all the given options, biogas is not a fossil fuel.

Nuclear energy is generated by the process of nuclear fusion or nuclear fission.

Nuclear fission is a process in which nucleus of heavy elements like uranium divides into two smaller nuclei when bombarded with some neutron. During fission of uranium, 200MeV energy is released.

True

Solar energy is a renewable energy in true senses. We can never ever face any shortage of solar energy. Solar energy will be available till the date of existence of sun which is expected to be 5 more billion years.

True

Solar heating devices as the name suggest are devices which use solar energy for heating a substance. While constructing the solar heating devices, reflectors are used to concentrate the sun heat to a single point for getting better results.

False

black surfaces are actually the best absorbers of heat. This is the reason, why it is suggested to avoid wearing black colored clothes on summer days.

True

The glass plate in a solar heating device does not allow the heat to escape. This phenomenon is used in solar cookers as the solar cooker box is covered with a plane glass plate so as to capture more and more ultraviolet rays of the sun and allow maximum heating of the food placed in the box.

True

Concave reflectors are used in solar heating devices because concave reflectors converge all the radiations to a single focal point and thus can increase the temperature at that specific point.

True

Solar cells are made up of Silicon which is a p-type semiconductor. Thus the given statement is true.

True

Selenium makes more efficient solar cells which converts a great percentage of solar energy into electrical energy.

False

Solar cells & solar panels can be used in remote areas.

Kamuthi solar power project is an ongoing project in Kamuthi town of Tamil Nadu which is going to be the world's largest solar power project. This Kamuthi is a very small town and a remote place in Tamil Nadu.

So, the given statement is proven wrong.