Sources of energy Worksheet-4

Sources of energy Worksheet-4


  1. How much solar energy is received by 5m2 in 2 hour? Given solar constant = 1.4 kW/m2.                       


  1. If the solar energy received in 5 minutes by 10m2 area is 4200 kJ, find the value of solar constant


  1. Calculate the heat energy received by 5m2 area on the Earth's surface in 1 minute, assuming that 47% of the solar energy strikes the Earth's surface.


  1. The surface area of a concentrator type solar cooker heater is 5m2. It reflects 80% of the radiation incident on it. Calculate the energy concentrated by the heater in 1 hour if the solar energy were delivered to it at the rate of 0.66 kW/m2.


  1. What is a good fuel?


  1. If you could use any source of energy for heating your food, which one would you use and why ?


  1. What are the disadvantages of fossil fuels?


  1. Why are we looking for alternate sources of energy?


  1. How has the traditional use of wind and water energy been modified for our convenience ?


  1. What kind of mirror-concave, convex or plane-would be best suited for use in a solar cooker ? Why?



  1. Solar energy received

= solar constant × area × time

= (1.4 kW/m2) (5m2) (2 × 60 × 60s)

= 50400 kJ (1 W = 1 J/s)


  1. Solar constant

= 1.4 kW/m2   (1 W = 1 J/s)


  1. Heat energy received

= 47% of solar constant × area × time

= (47/100) (1.4 kW/m2) (5m2) (1 × 60s)

= 197.4 kJ


  1. Energy concentrated

= 9504 kJ


  1. Good fuel has high calorific value or it produces large amount of heat on burning completely in air or oxygen,

It produces less smoke on burning,

It has low cost.

It is easily available,

It has an ignition temperature that is well above the normal temperature.


  1. A microwave oven can be used for heating the food as it heats the food uniformly and cleanly and there is no loss of nutritional value of food.


  1. Coal, petroleum and natural gas etc. are the examples of fossil fuels, they have the following disadvantages :

(i) They are non-renewable sources of energy.

(ii) By burning fossil fuel  air pollution is caused .

(iii) Carbon-dioxide produced by burning these fuels produces greenhouse effect.

(iv) The oxides of carbon, nitrogen and sulphur which are released on burning these fuels lead to acid rain that affects our water and soil resources.


  1. Fossils fuels were formed due to extraordinary conditions that prevailed on the Earth million of years ago. No new reservoirs of these fuels are being formed now due to the absence of those conditions. Fossil fuels are non-renewable sources of energy and if we continue to use these sources, we would soon be deprived of these sources. That’s why we should conserve these sources and look for alternate sources of energy.


  1. The traditional use of wind energy has been modified by using windmills and that of water by constructing hydroelectric power plants.


  1. A concave mirror is suitable for use in a solar cooker. Because a concave mirror reflects and concentrates solar energy from over a large area into a small area. Such a mirror is called a solar concentrator.