MAGNATIC FIELD

Region arount a magnet,electric current or changing electric field in which current is stationary, while that arount an alternating curret or changing direct current is continuously changing. Magnatic field are commonly reprecented by continuous lines of force or magnatic flux that emerge from north-seeking magnetic poles and enter south-seeking poles. The dencity of the lines indicate the magnitude of the field, the lines being crowded together the magnatic field is strong. The SI unit of Magnatic flux is the weber.

Beneficial Effects of UV radiation

A positive effect of UVB exposure is that it induces the production of vitamin D, in the skin. It has been estimated that tens of thousands of premature deaths occur in the United States annually from a range of cancers due to vitamin D deficiency. Another effect of vitamin D deficiency is osteomalacia (the adult equivalent of rickets), which can result in bone pain, difficulty in weight bearing and sometimes fractures. Other studies show most people get adequate Vitamin D through food and incidental exposure.
Many countries have fortified certain foods with Vitamin D to prevent deficiency. Eating fortified foods or taking a dietary supplement pill is usually preferred to UVB exposure, due to the increased risk of skin cancer from UV radiation.
Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as psoriasis and vitiligo. UVA radiation can be used in conjunction with psoralens (PUVA treatment). UVB radiation is rarely used in conjunction with psoralens. In cases of psoriasis and vitiligo, UV light with wavelength of 311 nm is most effective.

Ozone Deplection

Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole.
In addition to this well-known stratospheric ozone depletion, there are also tropospheric ozone depletion events, which occur near the surface in polar regions during spring.
The detailed mechanism by which the polar ozone holes form is different from that for the mid-latitude thinning, but the most important process in both trends is catalytic destruction of ozone by atomic chlorine and bromine.[1] The main source of these halogen atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds, commonly called freons, and of bromofluorocarbon compounds known as halons. These compounds are transported into the stratosphere after being emitted at the surface. Both ozone depletion mechanisms strengthened as emissions of CFCs and halons increased.
CFCs, halons and other contributory substances are commonly referred to as ozone-depleting substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths (270–315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol banning the production of CFCs and halons as well as related ozone depleting chemicals such as carbon tetrachloride and trichloroethane. It is suspected that a variety of biological consequences such as increases in skin cancer, damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.

RAINBOW

Series of concentric, coloured arc that may be see when light from a distant soure-usually the sun-falls on a collection of water droups such as in rain, spray or fog. The colered ray of the rain bow are caused by the refraction and total intanel raflection of light ray that enters the drop,each colour beeing bend through slightly different angle.Hence yhe different colours are spread upon emerging from the droup.The most brilliant and most common rainbow is the so-called rainbow,which results from light that emerges from the drop after one internal reflection.The colour of the arc (from outside to inside) red,orange,yellow,green,blue,indigo and violet. Occationaly a less-intese secotary bow may be observed;it has its colour sequence reversed.

MAGNATIC FORCE

Attraction or repulsion that arises between electrically charged particles that are in motion. While only electric force exist among stationary electric charges, with both electric and magnetic force exist among moving electric charges.The magnetic force between two moving is the force exerted on one charge by a magnetic field created by other.This force is zero if the second charge is travelling in the direction of the magnetic field due to the first and is greatest i it travels at right angle to the magnetic field. Magnetic force is responsible for the action of electric motor and the attraction between magnet and iron.