Category Science

What is ozone gas?

          Ozone is a form of oxygen in which each molecule contains three atoms of oxygen instead of the usual two. Its chemical formula is  and the three atoms are arranged in a triangular shape. This means that although its molecules contain only oxygen atoms, their number and arrangement differ from that of oxygen gas.

          Ozone is light blue in colour and has a strong odour. The characteristic smell can be experienced near running electric motors. It is poisonous in nature, differing considerably from oxygen in its chemical properties. It is found in the atmosphere in very small quantities, the highest concentration being at high altitudes where it is formed by the reaction of ultraviolet rays on oxygen.

          To obtain ozone, ordinary oxygen is passed through a tube where it is subjected to a silent electrical discharge. The electrodes are covered with insulating materials (glass or mica) so that the discharge currents are kept low, and high voltage pulses are supplied between the electrodes. This method has to be used so that oxygen acquires the energy it needs to form ozone but at the same time ozone does not become so hot that the molecules again break up into ordinary oxygen.

          Ozone is a powerful oxidizing agent. It is used to sterilize water, to purify air, to decolourize foods, and act as bleach. Its ozonide-forming property is used in several industrial processes in the manufacture of drugs and plasticizing materials.

          An ozone layer in the atmosphere absorbs much of the sun’s harmful ultraviolet rays and consequently saves the animal and plant lives on Earth. This is due to the fact that the ultraviolet rays spoil the vegetation and cause diseases like cataract and skin cancer. Recently the discovery of holes in the ozone layer created a great concern and hence the use of substances like chlorofluorocarbon (CFC), which are responsible for the depletion of the ozone layer, is being gradually eliminated.

 

What is a rain forest?

          A rain forest is a warm and rainy place with a thick growth of trees. Because of heavy rains, the trees grow tall and close together. The tree tops are so thickly branched that they almost block the passage of the wind. The air is still and uncomfortable. The thick tree top also prevents sunlight from reaching the ground. It is difficult to walk through these areas. Along with a large number of trees, it also has many different kinds of animals. These include noisy birds, hungry crocodiles, lizards, snakes and jaguars. Thousands of insects of different types are also found in the rain forests. There is an ant called ‘army ant’     that eats anything that would not move out of its way. There are certain mosquitoes whose bite is fatal; sweat bees which crawl into people’s ears and noses, and ticks and flies bite their skin.

          Most rain forests are located near the equator. The largest rain forest is the Amazon basin in South America. The temperature ranges from about 20 to 34°C. Thunderstorms occur about every three days. Areas of rain forests experience heavy rains upto 250 cms (100 inches). The tallest trees of rain forest form a covering of leaves called the upper canopy. The upper canopy may be 30 to 46 m above the ground. Smaller trees form lower canopies. The shade from the trees prevents about 99 percent of the sunlight from reaching the ground. Thus there is not much plant life on the forest floor. Dense vegetation close to the ground occurs in clearings and along rivers. These areas are sometimes called jungles.

          There are different kinds of plant and animal life in rain forests. Tropical rain forests contain the greatest variety of wild life including the wealth of insect life. Many of these insects have wonderful forms of camouflage. Also more different species of trees are found in tropical rain forests than in any other kinds of forests in the world. The soil layer in the tropical rain forests is very good for farming. 

What are pesticides?

            Any plant or animal that occurs in such abundance as to pose a distinct threat to man or his interests is called a pest. And the chemicals used for mitigation, control or elimination of such plants or animals are known as pesticides. Today we have algaecides, defoliants, herbicides, plant growth regulators and fungicides in use to control the growth of undesirable plants which compete with crops or other useful plants. Attractants, insecticides, miticides or acaricides, molluscicides, nematocides, repellents and rodenticides are used to reduce parasitism and disease-transmitting organisms in animals, crops, plants, foods, textiles and human beings.

            Most of the pesticides are chemical compounds and act in a similar fashion, i.e. by blocking some metabolic process. They, however, differ in composition, potency, mode of action, speed of effect. So different pesticides are used at different stages of infection. 

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What was the Stone Age?

          The Stone Age probably began more than three million years ago. It faded away some 5000 years ago and was succeeded by the Bronze Age. This period has been described as the landmark in the human history when man learned to make and use stone tools. This was followed by the metal age when people learnt the use of metals. 

          The Stone Age has been divided into three periods: the Paleolithic or Old Stone Age; the Mesolithic or Middle Stone Age and the Neolithic or New Stone Age.

          The Paleolithic or the Old Stone Age essentially began with the appearance of the first ‘hominids’ or man-like forms such as the australopithecines. The Paleolithic men were all hunters. Their tools were generally crude and made by flaking. The oldest Paleolithic tools are about 2,500,000 years old. It is likely that apart from the stone tools, the earliest hominids also used tools fabricated from wood and bone. The Pleistoce Epoch began about 2,500,000 years ago and lasted until about 10,000 years ago. During the latter part of the Old Stone Age, people had learned the art of making paintings on the cave walls. They had also learned the sculpture work.

          The Mesolithic period or the Middle Stone Age usually refers to that period when in the north-western Europe certain advancement started in about 8000 BC and lasted until about 2700 BC. During this period finer stone tools were made. The hunters used tiny flakes of flint in arrows and harpoons.

           During the Neolithic or New Stone Age, farming and the manufacture of pottery became widespread in Europe. The New Stone Age began in the Middle East about 9000 years ago. The people in the New Stone Age manufactured smooth axe heads of ground stone as they learned to grind and polish stones. The domestication of animals was an important factor in Neolithic life as was agriculture, including the plant care and growing of crops. This was the period when mining also came to be practiced. By this time agriculture had started and the people started forming villages.

          When the Europeans discovered America most of the Native Americans (Red Indians) were living in a Neolithic state. Some Australian aborigines and tribes in New Guinea still lead largely a Stone Age life.

What are whispering galleries?

          A whispering gallery is a place where a whisper is audible anywhere or everywhere inside it. Such galleries are made in circular buildings. Their working is based upon successive reflections of sound from its opposite walls. Since there is no loss of energy, the sound of a whisper can be heard at a great distance inside the gallery. For receiving a clear whisper, the ear must be kept close to the wall of the gallery, and it would sound as if the walls are whispering. Hence this name.

          The St. Paul’s Cathedral in London has the most famous whispering gallery. It runs around inside its dome. If you speak inside this gallery the sound waves of your voice would be carried round to the opposite side of the gallery.

          It happens because the waves are successively reflected from the walls and are prevented from going outwards by the stones lining the circular wall.

          The great dome of St. Paul’s has, in reality, two domes — an outer dome with a diameter of 148 feet, and an inner dome whose diameter is 103 feet. The hollow space between the two domes acts as a whispering gallery. There is a whispering gallery in Lucknow Imambara too. Many visitors come to see it.

How does a steering wheel make a car turn?

               The word ‘steer’ means to guide and control the course of a moving thing like a car, a ship or, any other vehicle. Every automobile is fitted with a steering wheel. The purpose of this steering wheel is to turn the automobile in the desired direction. Do you know how the steering wheel turns an automobile?

               The steering wheel is connected to a long metal bar. It extends into a metal gear box in the front of the car. When one turns the steering wheel, the bar turns the gear. In many cars the gear is a ‘worm gear’. This worm gear turns another gear which is connected to a lever. The lever is connected to two rods. One rod is attached to the left front wheel, and the other to the right front wheel. So when the steering wheel is turned, the gear moves the lever. The rods attached to the lever make the front wheels of the car turn left or right. 

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