Science Question Answer (1 Marks)

The calorific value of LPG is 55000KJ/ Kg. It means when 1Kg of LPG is burned completely, then 55000KJ of heat energy is produced.

The outermost zone has the highest temperature in the flame. It is the hottest part of the flame. It is quite thin as compared to middle zone.

Explosive combustion is the combustion in which a substance burns suddenly and produces heat, light and sound with the help of external source of heat or pressure. E.g.:- explosion of crackers on applying heat or pressure.

Calorific Value is the term which is used to express the efficiency of a fuel.

LPG and petrol catch fire at very low temperature and thus have low ignition temperature, while wood and coal have high ignition temperature.

The use of diesel and petrol as fuels in automobiles is being replaced by CNG (Compressed Natural Gas), because CNG produces the harmful products in very small amounts. CNG is a cleaner fuel.

Those substances which do not burn are called non-combustible substances. For Example- Stone, cement, glass, bricks, soil, sand, water, iron nails, copper objects.

Carbon dioxide does not support combustion and hence is considered as the best fire extinguisher for fires involving electrical equipment and inflammable materials like petrol.

Incomplete combustion of fuels produces a very poisonous gas called carbon monoxide.

Molten wax (Solid), Kerosene oil (Liquid) and LPG (gas) are the substances which burn by producing flames.

In the outer zone complete combustion of the fuel takes place, so colour of the flame is blue and it is the hottest part of the flame. It is the non-luminous part of the flame.

Those substances which can burn are called combustible substances. For Example- Cloth, straw, cooking gas, kerosene oil, wood, coal, charcoal etc. A combustible substance is called as fuel.

Petrol has a lower ignition temperature. Kerosene molecules are larger than petrol molecules and hence don’t mix easily with oxygen present in air. Thus, it has higher ignition temperature than petrol.

CNG and methane have the highest calorific value. Both of them have calorific value of 50000 KJ/Kg.

When white phosphorus is left out open in the room temperature for some time, it burns all by itself.

Coal has the lowest calorific value. Coal contains moisture. When coal burns the moisture in coal evaporates taking away some heat of combustion which is not available for our use.

Rapid combustion is the combustion in which a substance burns rapidly with the help of an external source and produces heat within a very short time. E.g.:- Burning of LPG.

Spontaneous combustion is the combustion in which a substance burns spontaneously and produces heat and light without the help of external source of heat. E.g.:- phosphorus burns spontaneously at room temperature.

Water is conductive in nature and hence the electricity in the equipment could reach the extinguisher (the person dousing the fire using water) and can electrocute him/ her.

Charcoal does not vaporize and so does not produce a flame.

As it is a closed tank full of petrol, there will be no supply of air. Hence the petrol will not catch fire as air is necessary for the combustion of petrol.

Flame is the zone of combustion of a combustible substance. Substances which vapourise during burning produce flames. E.g.:- kerosene, wax etc.

Incomplete combustion of fuels produces a very poisonous gas called carbon monoxide.

In the middle zone partial combustion of the fuel takes place, so the colour of the flame is yellow and it is moderately hot part of the flame. It is the luminous part of the flame.

The amount of heat produced by the complete burning or combustion of 1 Kilogram of a fuel is called its calorific value. The calorific value of a fuel is expressed in the unit of Kilojoules per kilogram.

It is measured in units of energy per unit of the mass of the substance, such as: kJ/kg, J/Kg.

Charcoal does not vaporize and so does not produce a flame.

A flame consist of three zones. These are Innermost zone, middle zone, outer zone. The three zones of a flame have different colors and different temperature.

Substances which vapourise during burning, produce flames, such as wax in the candle, Kerosene.
Substances which do not vapourise during burning, do not produce flames. Example- coal and charcoal.