Lakhmir Singh Physics Class 10 Solutions Page No:140
Question 1: A hydro-power plant converts one form of energy into another. Name the two forms of energy.
Solution : Potential energy into electrical energy.
Question 2: What type of energy is possessed by flowing water ?
Solution : Kinetic energy.
Question 3: Flowing water can rotate a turbine. Which type of energy is used up by the turbine ?
Solution : Kinetic energy of water.
Question 4: Name the original source of wind energy.
Solution : Sun.
Question 5: What should be the minimum wind speed for the satisfactory working of a wind-powered electric generator ?
Solution : 15 km/hr.
Question 6: Write one use of wind energy (a) in the past (b) at present.
Solution : Use of wind energy
(a) in the past – in flour mills
(b) at present – for generating the electricity through wind-powered generators.
Question 7: Why is the copper tube of a solar water heater painted black from outside ?
Solution : Copper tube of solar water heater is painted black because black colour is good absorber of heat.
Question 8: What type of reactions occurring inside the sun produce solar energy ?
Solution : Nuclear fusion.
Question 9: Name some of the solar energy devices.
Solution : Solar water heater.
Question 10: What type of reflector is used in a box-type solar cooker ?
Solution : Plane mirror reflector.
Question 11: What is the range of temperature which can be achieved in a box-type solar cooker in two to three hours ?
Solution : About 1000C to 1400C
Question 12: Name the device which converts sunlight into electricity.
Solution : Solar cell.
Question 13: How much solar energy will be received by 1 m2 area in one hour if the solar constant be 1.4 kW/m2 ?
Solution : Solar constant is 1.4kW/m2 or 1.4 kJ/s/m2.
Solar energy received by 1 m2 area in 1 s = 1.4 kJ
Solar energy received by 1 m2 area in one hour (or 3600 s) = 1.4 x 3600 = 5040 kJ
Question 14: Fill in the following blanks with suitable words :
A solar cell converts………. energy into…………. energy.
Solution : sunlight; electrical.
Question 15: (a) What is the difference between a thermal power plant and a hydro power plant ?
(b) Which of the two causes serious air pollution and how ?
Solution : (a) Difference between thermal power plant and hydro power plant:
Thermal power plant uses non-renewable sources of energy like coal, oil or gas; whereas hydro power plant uses renewable source of energy i.e. water.
Thermal power plant causes pollution due to the burning of fossil fuels; whereas hydro power plant is environment friendly.
(b) Thermal power plant causes serious air pollution because it emits harmful gases and fly-ash into the air.