Category Science

In a steam turbine, hot water vapours flow from jets onto a rotor having several propeller-type shovel blades. There is a high pressure in front of the turbine, while a low pressure is maintained at the back. As a result, the steam shoots at high speed through the turbine transferring its energy to the rotor. The movement of the turbine is converted into electrical energy, through generators. Steam turbines are used mainly in coal-fired engines and nuclear power plants. The turbines of large power plants are up to 6o m long and weigh several hundred tons. Several rotors are connected in them one after the other. 

In a pressure cooker, the food is cooked at a higher temperature than in normal vessels. Pressure cookers are closed and air-sealed vessels that do not permit air or liquids to escape below a preset pressure. Upon heating, water evaporates inside the cooker and the steam pressure starts building up. The water then starts boiling at this higher pressure. This lets the potatoes cook faster. Pressure must be released before opening the cooker by letting it cool down or by opening a drain valve carefully. 

Burning is a very fast chemical reaction in which a fuel combines with oxygen, releasing heat and light. Each substance has its own ignition temperature. Thus, some substances which have a low ignition temperature catch fire easily, while others with a high ignition temperature catch fire with difficulty. The size of the surface is also important, which reacts with the oxygen in air. A big log of wood cannot be ignited with a single matchstick, but fine wood shavings can be ignited very easily. A flame arises only when a substance burns in the gaseous state. In case of wood, the oil vapours in the wood burn, which give the typical smell of the wood?

The secret of the candle lies in the wick. A matchstick ignites the wick. The heat of the flame melts the wax of the candle. The liquid wax rises up in the wick, and more it evaporates, more higher it rises. The vapour burns. Wax is made up of carbon and hydrogen. Both elements react with oxygen during burning, whereby water vapour, soot, and waste gases like carbon monoxide and carbon dioxide are produced. This also gives the colours to the candle flame – yellow light from carbon and the blue light from water vapours. 

A fire starts with the ignition of a substance by a source that provides the necessary heat to the substance. This source can be a matchstick, an electrical spark, or the effect of a burning lens, such as a magnifying glass. The required temperature for ignition depends on the material. Paper burns at temperatures starting from 190°C, wood at 280°C, and cotton at 450°C. Therefore, a pair of jeans does not catch fire quickly, while a piece of paper catches fire very quickly. Once a substance starts burning, its intensity depends on the supply of oxygen. For this reason, windows and doors of a building should always be kept closed in case of a fire. 

The finer the water is sprayed on a fire, the faster it evaporates. As a result, it takes away energy from the flames and cools down the burning substance to such an extent that it can no longer catch fire again. Water extinguishes fire by creating a film of water over the burning substance, and thus cutting off its oxygen supply. Water has many advantages such as it is non-toxic in nature and is available in plenty. Water can be used to extinguish fire as discussed above, but this is not true in all cases of fire, for example, oil burning in a pan can be extinguished better by covering it with a lid rather than using water, burning metals would split the water chemically through the heat, and oxygen will be released which will intensify the fire further. Similarly, water cannot be used in cases where the fire has originated due to an electric fault.