Category Science

How does an electric fan function?

               Electric fans have become an essential part of our lives. It provides a cooling effect during the summer and rainy seasons. Do you know how does it work?

               An electric fan is a device which converts electrical energy into mechanical energy. It works on the basis of magnetic effects of electrical currents.

               The heart of an electric fan is an electric motor. So before understanding the working of a fan, it is essential to know the working principle of an electric motor.

               In its simplest form, it consists of a coil or armature through which the current flows. It is connected with a spindle. This coil is placed in between the poles of a magnet. When the electric current flows through the coil, it starts rotating due to the magnetic effects of electric current. This motor consists of a split-ring commutator to which two carbon brushes are attached. The armature of the motor is connected to a metal shaft. At the other end of the shaft, three or four blades made of a light metal are attached which also start rotating along with the motor. These blades are designed in such a way that when they rotate, they suck in air from one side and throw it to the other side, thus causing strong air currents. 

               The speed of rotation of the motor can be controlled by controlling the current which is done with the help of a regulator. This regulator consists of a resistance which controls the amount of electricity flowing through the coil.

               Usually electric fans are of two types: ceiling fans and table fans. The domestic electric fans are usually rated from 60 watts to 120 watts.

               A third type is often used in underground establishments, kitchens, cinema halls, stores etc. to expel the polluted air. These are called exhaust fans. The blades of these fans are so designed that they suck in the air from inside and throw it outside. These are also used in air coolers.

               Now the question arises as to how the air of the fan gives us the cooling effect? The fan increases the speed of air currents and this brings about an increase in the rate of evaporation. Since evaporation causes cooling, a running fan produces a cooling sensation.

 

How is wax made?

            Wax is an insoluble solid fatty substance that is widely used as a protective covering for different kinds of surfaces. It is also used for making candles and polishes. Waxed paper is an item of our daily use. Do you know how wax is made?

            Normally wax is solid at room temperature but softens and becomes sticky when heated. Many fruits and vegetables, and leaves of many plants have a thin protective coating of wax. It is useful in protection of organisms. Many animals also produce wax. We get wax in large quantities from minerals and petroleum. Nowadays synthetic methods have been developed for the manufacture of wax.

             Depending upon the source from which wax is obtained, we classify wax into four kinds: (i) mineral wax (ii) animal wax (iii) vegetable Wax and (iv) synthetic wax. Paraffin wax is a kind of mineral wax which is taken out of petroleum. This is quite hard in nature. Petroleum jelly is a kind of soft wax and is used for medicinal purposes. More than 90 percent of all commercial wax used today is petroleum wax. This is very useful because it is odourless, tasteless and chemically inactive.

            Animal wax, such as bees wax produced by bees, is used for making candles, cosmetics, polishes, crayons and artificial flowers. We get wool wax from wool-bearing animals and are called lanolin when purified. Lanolin is widely used for manufacture of moisturizer and skin creams.

            We get several kinds of wax from plants. Carnauba wax is obtained from the leaves of the carnauba palm trees of Brazil. This wax is hard and gives an excellent brightness when used as a floor and furniture polish. Candellilla wax comes from a plant of the same name that grows in Mexico and the South Western United States. It is a brown wax used in phonograph records, floor dressings and candles. Bay berry wax from the berries of this shrub is used for making candles.

            Synthetic waxes are chemical combinations of hydrogen, carbon, oxygen and sometimes chlorine. They are made according to different formulae to have definite properties.

 

How do a mixer and grinder work?

               Mixer and grinder are very useful domestic appliances. With the help of these appliances we can grate, grind and prepare mango shake, milk shake, cold coffee etc. in a short period of time. Butter can be extracted from cream by using this apparatus. Pulses and spices can also be ground easily with its help.

               This apparatus consists mainly of two parts. One is the base of the apparatus which is fitted with a high speed motor. This motor makes 15-20 thousand revolutions per minute. It also consists of a variable switch by which the speed of the motor can be adjusted with the other part of the apparatus known as a mixer and grinder. This is usually made of stainless steel or plastic in the shape of a jar. It is fitted with blades which revolve with the speed of the motor. This rotating blade minces the food material into small pieces.

               Modern mixer and grinders also consist of other attachments such as a juicer with the help of which we can extract the juices of apples, oranges, tomatoes and other fruits and vegetables. In this attachment juice pours out on one side and pulp from the other side. Most modern grinders and mixers can be fitted with various other attachments such as a slice grater, meat mincer, dough maker etc. Nowadays we have grinders by which even wheat or maize can be ground.

               These electrically operated machines have minimized the tedious work in a kitchen. Not only do these machines save time but also provide neat, clean and tasty food for us. Moreover, these machines do not consume much electricity.

What is Greenhouse Effect?

               We all know that rapid industrialization and modernization of technology from field to factories, from laboratory experiments to space exploration are closely linked with energy generation. But during the last century man’s activities, principally concerning energy development, have caused fossil burning wantonly. This has raised the atmospheric concentration of Greenhouse gases leading to an increase in the average global temperature which is called “Global warming”.

               What actually is the “Greenhouse effect”? Our earth reflects a lot of energy back into the atmosphere. But presence of heavy carbon-dioxide in the atmosphere prevents some of this heat escaping just as a glass or plastic sheet stops escaping heat from the so called “Greenhouse” used to protect growing plants. The main Greenhouse gas is carbon-dioxide. The source of this gas is from fossil fuel combustion like coal, petroleum and natural gas. Methane, Chlorofluorocarbon (CFCs) and Nitrous oxide are among the other Green house gases. The sources of such gases range from Bio-mass burning, fumes emitted from refrigeration and air conditioning plants (Freon gas), industrial fumes and enteric fermentation of cattle, insects and different crops.

               Scientists believe that earth’s temperature will rise markedly in next 50 years. Between the present time to 2025 AD, it may rise by 1°C and further by 3°C during 2025-2100 AD. This would alter significantly the earth’s ecological balance, its normal cyclic seasons, melting of polar ice caps and the ultimate rise in sea level submerging many land areas. Widespread flooding in coastal regions all over the world will occur and large part of world’s civilization may disappear beneath the sea.

               Scientists are engaged in search of ways and means to combat this impending danger under the guidance of the Paris based International Council of Scientific Unions (ICSU).

 

Which fish spits at insects?

               Fishes are the most numerous among vertebrates and their species number more than 30,000 which is more than all the other backboned animals put together. Each group has its own way of gathering food. The archer fish is such a fish which can shoot down insects from overhanging vegetation with water pellets. Its aim is quite accurate and it can easily dislodge a fly or a beetle about four feet away, so that it falls into water. The archer fish then dashes on the insect and eats it up.

               It is interesting to find out how the fish is able to project drops of water accurately over such a distance. The roof of its mouth forms a long groove. If the fish suddenly closes its gill covers, water is forced from the gill chamber into the mouth. At the same time the tongue is raised so the grooves become a long tube from which water squirts in a line of drops.

               Archer fish is a fresh water fish and belongs to the family Toxobidae. It is found in India and Indonesia. It got its name from the way it captures its food. Archer fish can also live in sea water. Toxotese jaculator is the most commonly known fish of this family. Its length can be upto 18 cm. Five groups of this fish have been studied. These fishes generally feed on insects. 

How do plants protect themselves from frost?

            There are over 350,000 kinds of plants in the world. All these continue to struggle to survive against storms, rains, sun and snow. There are some which die due to cold in winters, although before dying their seeds are spread on the ground so that in the autumn they can give birth to new plants. However, there are some plants which are able to protect themselves against winter.

            These plants are able to protect themselves against winter frost by a special method. They spread their leaves and flatten them against the ground. The warmth in the soil enters their leaves and the plant is protected. Some other plants like myrtle and heather allow their upper parts to die but their stem remains alive. Stems act as storage organs, both above and below the ground. These produce buds and thus restore their species. Many plants hide themselves under the soil to escape from the cold, these include tubers, bulbs and roots which store their food according to their need. When summer comes they push out green leaves and new buds.

            Sometimes artificial methods are used to protect plants from frost, e.g. oil heaters called smudge pots are used in the region where citrus fruits are grown. In some places large fans are used to keep the cold air moving so that frost is not able to get deposited on the fruit trees.