Chapter Review:

• Properties of good fuels (i) they doesn't  cause  air pollution (ii) Which would do a large amount of work per unit volume or mass. (iii) Be easily accessible.

• Coal, petroleum and natural gas are called fossil fuels. As Such fuels were formed by the slow decomposition of fossils (remains of plants and animals) which got buried under the surface of earth and take millions years to form. 

• Energy can only be converted from one form to another. It can neither be created nor destroyed. The total energy before and after the transformation remains the same. This law is valid in all situation and transformation. That is called the law of conservation of energy. 

• The turbine works by mechanical energy which it gets from various sources like water energy, Wind energy and nuclear energy etc.

• Some gases like CO₂ and methane traps heat from sun rays. Our atmosphere does not allow the radiations to go out. This is called green house effect.

• Oxide of sulpher and nitrogen react with water vapour in atmosphere and produce acidic substance, its rain is called acid rain.

• The source of energy obtained from plants and animals said to be Bio-mass. Ex-: Wood, cow-dung etc. 

• Mixture of cow dung and water is said to be slurry. 

• The black colour absorbs heat more frequently than others.

• Solar cell is a device which converts sunlight into electricity.

• Silicon metal is used for making solar cell. 

• Silver metal is used for interconnection of solar cells.

• The dynamo convert the mechanical energy into electrical energy.

• Geological changes, molten rocks formed in the deeper hot regions
  of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’.