CBSE(NCERT) GRADE 10 ENGLISH 2022 SET4

Sifting through the sands of time 1 untains, skeletons of marine animals, even tiny diamonds. Sand provides a mineral treasure- -changing processes. 2 Sand : as children we play on it and as adults we relax on it. It is something we complain about when it gets in our food, and praise we would discover an account of a geological past and a history of marine life that goes back thousands and, in some cases, millions of years. 3 Sand covers not just sea-shores, but also ocean beds, deserts and mountains. It is one of the most common substances on Earth. And it is a major element in man-made items too concrete is largely sand, while glass is made of little else. 4 What exactly is sand ? Well, it is larger than fine dust and smaller than shingle. Depending on its age and origin, a particular sand can consist of tiny pebbles or porous granules. Its grain may have the shape of stars or spirals, their edges jagged or smooth. They have come from the erosion of rocks, or from the skeletons of marine organisms which accumulate on the bottom of the oceans, or even from volcanic eruptions. 5 grains may be derived from nearby coral outcrops, from crystalline quartz rocks or from gypsum. On Pacific islands jet black sands form from volcanic minerals. 6 Usually, the older the granules, the finer they are and the smoother the edges. The fine, white beaches, for instance, are recycled from sandstone several hundred million years old. Perhaps they will be stone once more, in another few hundred million. 7 Sand is an irreplaceable industrial ingredient whose uses are legion : but it has one vital function you might never even notice. Sand does a better job of protecting our shores than the most advanced coastal technology.

Extraction And Purification Of Drinking Water 1 Some consumers choose to purchase bottled drinking water, rather than relying on city tap water supplies. Bottled water has typically been extracted from underground sources. If water exists underground, but has no natural exit points, bottling companies may construct a water table well by drilling down to extract water from an unconfined aquifer. This is done when the surface is lower than the natural water table. In some cases, as with a valley or gully on a mountain, the level of the spring can emerge. Bottling companies are permitted to extract this water from a hole drilled into the underground spring, but the composition of the water must be identical to that of the naturally surfacing variety nearby. 2 Artesian water is drawn from a confined aquifer, a deep underground cavity of porous rock that holds water and bears pressure from a confining layer above it. This water can be accessed if companies drill a vertical channel down into the confined aquifer. Due to the pressurised nature of this aquifer, water will often rise up from within it and form a flowing artesian well, which appears as an explosive fountain at the surface. This happens when the surface is lower than the natural water table. If the surface is not lower than the natural water table, it is still possible to draw artesian water by using an extraction pump. 3 Bottled water has been subjected to a variety of cleansing processes. A common filtering procedure, known as reverse osmosis, involves the water being pressed through microscopic membranes that prevent larger contaminants from passing through. The microscopic size of these holes is such that they can even obstruct germs, but they are most effective against undesirable materials such as salt, nitrates and lime scale. One disadvantage of reverse osmosis is that a lot of unusable water is generated as a by-product of the procedure; this must be thrown away. 4 For treating pathogens, an impressive newer option is ultraviolet (UV) light. Powerful UV light has natural antibacterial qualities, so this process simply requires water to be subjected to a sufficient strength of UV light as it passes through a treatment chamber. The light neutralises many harmful germs by removing their DNA, thereby impeding their ability to replicate. A particularly impressive quality of UV light is its ability to neutralise highly resistant viral agents such as hepatitis. 5 The overall effects of UV light treatment are variable, however, which leaves many municipal water treatment processes relying on chlorination. Its powerful and comprehensive antimicrobial effect notwithstanding, chlorination is also extremely inexpensive and remains the only antimicrobial treatment capable of ensuring water remains contaminant-free all the way through the pipes and to the taps of domestic homes. Many members of the public remain suspicious of water that has been treated with such a harsh chemical. Its ease of use and affordability has meant that chlorine often plays an important role in making tainted water supplies safe for consumption immediately after natural disasters have occurred.