Scientific Explanations | Material for all Competitive Exams

Why it is dangerous to sleep in an unventilated room with fire burning?
▪ It is dangerous to sleep in an unventilated room with fire burning inside because the fire produces carbon monoxide and carbon dioxide gases. Carbon monoxide is poisonous and can cause death.

Alcohol is sometimes rubbed on the body of a person suffering from fever
▪ As soon as Alcohol is applied on the body, it evaporates taking away some heat from the body. Since evaporation has a cooling effect, the body temperature can be reduced by rubbing alcohol.

Why people used filament of an electric bulb of tungsten?
▪ The filament of an electric bulb is made of tungsten because it has a high melting point and can be heated to a high temperature to emit light.

Why Water kept in an earthen pitcher is colder than other pitcher?
▪ Water kept in an earthen pitcher becomes cold because the pitcher has minute pores on its surface which absorb water. Water in the pores evaporates when it comes in contact with air, and produces a cooling effect.

Why a sliced apple, when exposed to air, turns brown?
▪ A sliced apple, when exposed to air, turns brown after some time as it contains iron which gets oxidized and gives the fruit a brownish colour.

Moisture gathers on the outer surface of a glass tumbler containing cold water)
▪ Moisture gathers on the outer surface of a glass tumbler containing cold water) because the water vapours present in the air get cooled and appear as droplets of water on coming in contact with the cold surface of the glass tumbler.

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Green clothes appears Green when day light falls on it
▪Green clothes appear Green when day light falls on it because it absorbs all the constituent colours of white light except Green, which it reflects to us.

The freezing compartment inside a refrigerator is at the top
▪ The freezing compartment inside a refrigerator is at the top because the air in contact with it becomes cold and heavy and sinks downwards, cooling the rest of the compartment.

A copper vessel left in the air for a long time turns green
▪ A copper vessel left in the air for a long time turns green. This is due to the formation of copper carbonate when copper reacts with carbon dioxide and moisture present in the air.