LPG, an acronym for Liquefied Petroleum Gas, is the most popular cooking fuel used in urban households. It is a mixture of gases, liquefied by compression, consisting of volatile and flammable hydrocarbons such as ethane, propane, butane and pentane. It is obtained either from crude oil or from natural gas. Crude oil, recovered from underground oil deposits, is a mixture of heavy hydrocarbons. In a petroleum refinery, this oil is heated and turned into a mixture of gases and liquids. This mixture is then passed into a huge tower called fractionating column which is hotter at the bottom and cooler at the top. The heavier hydrocarbons with large number of carbon atoms condense at higher temperatures at the bottom whereas the lighter components with fewer carbon atoms condense at a lower temperature at the top. For LPG, the lower hydrocarbon fraction is collected from the top of the fractionating column in the gaseous form. These gases become liquid when kept under pressure. Since the hydrocarbons do not have any smell a small quantity of methyl, ethyl or terbutyl mercaptans, which have strong disagreeable odour, are added to LPG to make it easily detectable in case of leakage. LPG is also being used in automobiles as a fuel which is much cleaner than petrol.

Some kinds of liquid crystals can rotate the place of polarized light and this property is utilized in digital display unit used in watches, calculators, digital diaries and cameras.

The display unit is made up of a thin film of the liquid crystal sandwiched between two thin glass sheets coated with a transparent conducting material such as tin oxide which acts as the electrodes. On the top and bottom of the glass sheets are placed two polarizing filters or polarizer’s turned 90 degree with respect to each other. Since in the liquid crystal film the polarized light is entering from the top by 90 degree, the light can pass through the second polarizer also, and when reflected from a mirror placed below the second polarizer, the display panel appears clear. When a small voltage is applied across one or more electrodes which are laid on the glass in the shape of alphabets, digits or symbols, the molecular alignment in the respective regions of the liquid crystal film is altered and they no more rotate the polarized light. This makes the characters on the display unit appear black on a clear background. Liquid crystal displays are quick acting and consume negligible power.

Any unwanted form of sound, such as noise of vehicles, machinery, jet planes, indiscriminate use of loud speakers, are examples of noise pollution. Just as we measure temperature on Celsius scale, the level of noise is measured on the decibel scale (dB). There are mainly three different sources of noise pollution: industrial machinery, transportation, and community activities and entertainment.
Constant exposure to noise levels above 75 decibels can damage the ear and impair hearing. Exposure to noise levels above 120 decibels causes pain in the ear, and continuous exposure to noise levels above 180 decibels may even cause death. Road traffic noise is usually of moderate intensity, but being of continuous nature can be irritating to people living along busy streets. Badly maintained vehicle engines and indiscriminate use of horns often make the situation worse leading to various types of physiological disorders such as high blood pressure and heart problems. Loud noise is even known to affect unborn babies. Sudden loud noise such as gunfire or crackers can cause irreversible damage to ear-drums.It will affect all people in all ages and mostly heart patients will be affected by sudden noise raise and over noise will increase their blood pressure which will cause some sort of pain in heart.