Write short notes on any four of the following . (a) Green house effect (b) BOD & COD (c) Tensile strenght (d) E-waste (e) electrochemical (f) rusting

Q. Write short notes on any four of the following .

(a) Green house effect                            (b) BOD & COD

(c) Tensile strenght                                 (d) E-waste

(e)   Electrochemical                               (f) Rusting

ANSWER :- (a) Green house effects :- CO2 gas in the atmosphere perform major role of heating up of the atmosphere due to trapping of infra red rays (from the sun). This is called green house effects. The sunrays consists of UV, visible and infrared radiation. The ozone layer (present in the upper atmosphere ) absorbs most of the UV radiation and allows visible and infrared radiation to pass throgh towards the earths . Since infrared rays are the short wavelenght, so they easily pass through the CO2 layer in the atmosphere. These infrared rays cause heating effects to the objects on the earth and atmosphere on the earth. consequently, if large amount amount of CO2 is present in the atmosphere, it causes greater heating up of the earth's atmosphere. Hence the teperature of the earth's atmosphererises. Every year the world-wide concentration of CO2 is increasing of a rate of 0.75 PPM and the temperature is rising at a rate 0.05C per year . If the cThis could utimately melt the glaciers polar ice continues the world will go on warming up more and more. This cpould utimately melt the glaciers polar ice caps and result in flooring of msny low lying areas.

(b) BOD(Biological oxygen demand) :- BOD of a sewage is defined as amount of fre oxygen required for the biological oxidation of the organic matter under aerobic condition at the 20 degree celcius and for a peroid of 5 days. the unit of BOD of 100 and 150mg / litre. BOD is the  most important in sewage treatment as it indicates the amount of decomposition organic matter in the sewage.

COD(Chemical Oxygen Demand):- It is a measure of oxidisable impurities present in the sewage whereas, the BOD measures the oxygen consumed by living organisms. While assimilating organic matter present in the water, the COD is a measures of both the biologically oxidisables and biological inert organic matter such as cellulose consequently COD value . The COD values can beemployed to estimate approxmate BOD values. The main advantages the COD is that its determination takes about 3 Hours, comared to more than, compared to more than 5 days for the BOD detenation. 

(c) Tensile strenght :- Tensile strenght, maximum load that a material can support without fracture when being stretched, dividding by the original cross sectional area of a material. tensile strenght have dimensional of force per unit area and in the english system of measurement are commonly ex- pressed in unit of ounds per square inch, often abbreviated to psi. when stress less thenthe tensile strenght are removed, a material returns either completely or partially to its original shape and size . As the stress reaches the value of the tensile strenght, however, a material, if ductile, that has already begun to flow plastically rapidly forms a constricted region called a neck, where its then fractures.

(e) Electrochemical :- A electrochemical cell is device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called volatic cells or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells. A common example of a galvanic cell is a standard 1.5 volt cell means for consumer use.

(f) Rusting :- Rusting of iron refers to tje formation of rust, a mixture of iron oxides, on the surface of iron objects or structure.This rust is formed from a redox reaction between oxygen and iron in an enviroment containing water (such as air containing high level of mixtures ). The rusting of iron is characterized by the formation of a layer of a re,flacky substances that easily crumble into a powder.

                                   This phenomenon is a great example of the corrosion of metals, where the surfaces of metals are degraded into more chemically stables oxides. However, te term 'rusting' is generallyused to refer to the corrosion of objects made of iron or iron alloys.