Subject - General Science
Chapter : Gist of What, Why & How

Lie Detectors Work

• A lie detectors work on the principal that a person who tells a lie is nervous and under stress under these conditions his body undergoes some physiological changes.

• These includes increases in the blood pressure, heart beat rate and perspiration on hands and soles. These changes are monitored and detected by a lie – detector.

Night vision Glasses Work

• Night vision glasses, used for seeing in the pitch dark night, use the little light available to form an image of sufficient brightness to be screen.

• The image is first focused, as in a camera, on to a window which is coated with special chemicals containing sodium, potassium, cadmium and oxygen compounds which emit electrons when illuminated.

• The electrons so emitted are then accelerated by a series of powerful electric fields and made to fall into another screen coated with a fluorescing chemical which glows recreating a much brighter image of the original scene.

• Some night vision glasses make use of infrared radiation emitted by all objects even in the dark. These radiations are amplified in a similar way to make night vision possible.

Crude oil Refined

Crude oil that comes out of an oil well is a thick, dark liquid containing a mixture of many organic compounds. It cannot be put to use without refining. The different constituents of crude oil boil at different temperature. Refining processes may be classified as fractional distillation separates crude oil into some of its fractions depending on their boiling points. Some components are separated by solvent extraction in which an organic solvent is used to extract the substances especially solids which are then recovered by crystallization or evaporation of the solvent. Cracking is also a process used in refiners to produce useful petrochemicals. Here heat and catalyst are used to break down some of the heavier hydrocarbons to lighter, more useful fractions.

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AIDS Detected

• AIDS is caused by a virus called human immunodeficiency virus or HIV. The presence of this virus is detected by screening the blood of a person for special kinds of proteins called antibodies which are produced in the body in response to viral infection A characteristic feature of antibody molecules is that they are highly specific. They bind only to certain regions of the antigen. This is similar to a key fitting only a specific lock. AIDS detection tests are actually based on detecting the binding of the antibodies present in the blood with an artificially synthesized antigen attached to a solid surface.

Plants Capture Insects

• Certain plants which grow in soil poor in nutrients depend on insects for their nutritional requirement. These carnivores’ plants use a combination of deception and a trapping device to get their meals.

• Some insects – eating plants like the venus fl trap (dionaea musipula) have leaves moulded into twin blade traps with teeth like projections on their margins which interlock to trap any insect sitting on the leaf. Leaves of another plant names drosera have glandes all over them which secrete a sticky substance to trap insects. The pitcher plant has fluid filled pitches – shaped structure into which unwary insects fall and drown. All insects eating plants secrete digestive juices to digest their prey.

Artificial Rain Produced

• Rain occurs when the water vapour in the clouds forms water drops or ice crystals large and heavy enough to fall to the ground. This process is hastened if the cloud has tiny particles of matter for the water vopour to condense on. Artificial rain produced by introducing these particles into the clouds by a process called cloud seeding.

• Clouds can be seeded in different ways. The seeding agent can be sprayed into a cloud from an air plane or sent up in a rocket. If the wind is strong enough, it can be dispersed in the form of smoke from the ground. At cloud temperature above 0oC solid carbon dioxide or crystals of silver dioxide is used. Water vapour in the clouds condenses around the seeding agent to form rain drops. If the temperature is below 0oC ice crystals are formed. When the ice crystals pass through air warmer than 0oC, they melt and fall as rain. Artificial rain is best produced from moisture-laden clouds. It cannot be produced from a cloudless sky.

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