Question 1 Answer these questions on solar energy
(a) Why are black surface utilized for making solar cookers?
(b) What is solar cell? Name two materials mostly used for making solar cells?
(c) what are advantages and limitation of solar cooker?
(d) what is a solar power plant? Name one such plant in our Country
(e) what is the maximum temperature attained in a concave reflector type solar cooker?
(f) A student constructed a box type solar cooker. He found that it did not work efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the cooker. Solution
(a) A black surface absorbs more heat or energy as compared to white or reflecting surface under same condition
(b) A solar cell is a device which converts solar energy directly into electric energy. Silicon and germanium are the two most commonly used materials for making solar cells.
(d) Sunlight is concentrated on black painted pipes (filled with water) with the help of concave reflectors. Due to solar heat, water starts boiling and then changes into steam. The steam so produced rotates a steam turbine which drives a generator to produce electricity. A 50kW solar thermal power plant is being installed at the Twal Pahari Premises of the Solar Energy Centre, Gurgaon (Haryana).
(e) 2000 C
(f) The four possible mistakes in the construction and operation of the cooker are:
(i) The interior of solar cooker might not have been blackened,
(ii) Plastic cover might have been used instead of glass cover,
(iii) The cooker might not have been properly insulated,
(iv) The cooker utensils might not have been blackened.
How were fossil fuels formed? How these fossils fuels were made? Solution
Fossil fuels were formed due to high pressure, heat and the action of anaerobic bacteria of fossils for million of years. These fuels were made form the fossils of plants and animals buried deep in the Earth.
Why is Tungsten used almost exclusively for filament of electric lamps? Solution
Melting point of tungsten is very high so it is used for making filament of electric lamps
Fill in the blanks
(i)The major constituent of the Biogas ___________
(ii)Which of these gaseous fuel has higher calorific value (a) hydrogen (b) Methane (c) LPG (d) Biogas ____________
(iii) two gases, other than carbon-dioxide that are given out during burning of fossil fuels and contribute towards acid rain formation_________ Solution
(iii) Sulphur dioxide and Nitric oxide.
How is nuclear energy generated? Explain the process of producing electricity with Nuclear energy? Mention the major hazard of it Solution
To produce nuclear energy, a heavy nucleus is bombarded with a low energy neutron. In this process, it splits into two lighter nuclei with a tremendous release of energy which can be utilized to boil water to run turbines.
The major hazard of nuclear power generation is the storage and disposal of nucleus wastes because they are radioactive
Why Charcoal is better fuel than coal? Solution
(a) No harmful gases are produced on burning charcoal
(b) No residue is left after it has burnt itself out.
(c) It has a higher calorific value.
What are the good characteristics of a good fuel? Solution
(a) A good fuel which gives more energy per unit volume or mass
(b) It is easy to store and transport
(c) It should generate less pollution
(d) It should be harmful to the surroundings
Question 8 True and False Statements
(a) Acid rains happens because burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere.
(b) Ocean thermal energy is due to pressure difference at different level
(c) Sun is the ultimate source of energy
(d) Methane is not a constituent of biogas
(e) The potential energy of the high altitude wind is the source of wind power
(f) Charcoal and coal are both fossil fuels Solution
(b) False, Ocean thermal energy is due to temperature difference at different level
(d) false as it is present
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