Category Science & Technology

How do electrically heated appliances work?

Electric heaters, immersion heaters, electric irons, electric kettles, etc. are appliances which produce heat through electricity. All these appliances are based on the heating effects of electric current. When electric current is passed through a wire, it gets heated up. Heating of a wire depends upon two facts: first, on the resistance of the wire and then on the amount of electric current passed. The heat produced in the wire is directly proportional to the resistance of the wire and that of the square of the current. The amount of heat produced also depends upon the time for which the current passes through the wire.

Based upon this property of current, many domestic electric appliances have been developed. The working principle of all these appliances is almost the same, the difference lies only in their construction. An electric heater consists of a coil of nichrome wire which is in the form of a spring. This coil is mounted on an insulating base plate made of clay. When electric current is passed through the coil, it gets heated up. Room heaters are also made in a similar way, the only difference being that nichrome wire is wound around an insulating rod and a reflector is mounted at the back of the coil which reflects the heat radiation.

Immersion heaters also consist of a nichrome wire which is enclosed in a metal tube. To isolate the wire from the metal tube, an insulating powder is filled in the tube. This powder acts as an insulator for electricity but conducts heat. When the two terminals of the wire are connected to an electric source, the current starts flowing through the wire and it gets heated up. The immersion heater is put inside a bucket full of water to heat the water.

An electric iron is used to remove the wrinkles from washed clothes. This appliance also consists of a ribbon of nichrome wire which is enclosed between two sheets of mica. This spreads the heat uniformally along the base plate of an electric iron. Mica sheets are mounted on a heavy metal plate. This metal plate, when pressed against the surface of the cloth, removes the wrinkles from the cloth.

Electric irons are of two types: automatic and manual. Automatic one is fitted with a thermostat control which regulates the temperature. Manual irons do not have such a device. When the iron is cold, thermostat provides and maintains a constant temperature by the use of a device that cuts off the supply of heat when the required temperature is exceeded.

An electric kettle is used to prepare tea or coffee. It also consists of a heating element fitted at the bottom of the vessel and is isolated from it. Water is put into the vessel which gets heated when current is passed through the heating element.

For all electrically heated appliances, it is very essential to have an earth connection. Immersion heaters should not be switched on, until there is water in the bucket. The electric bulb is also a similar device whose filament gets heated up when the electric current is passed through it and it produces light.

 

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).

 

How does a parachute work?

               A parachute is an umbrella like device used for slowing down the descent of a body falling through the atmosphere. Originally it was conceived as a safety measure against a probable plane crash or some malfunctioning in a flying aircraft. The parachutes have now found wide applications in times of war and peace; for safe dropping of supplies of essential items in times of emergency as well as for landing of personnel. The first man to demonstrate it was Louis-Sebastian Lenormand of France in 1783. Andre-Jacques Garnaria was first to use a parachute on regular basis demonstrating a number of exhibition jumps including one from a height of about 2400 m in England in 1801.

               Early parachutes were made of canvas and later silk also came to be used. Captain Albert Berry of the U.S. Army made the first successful descent from an aeroplane in 1912. In World War II, parachutes were used for a variety of purposes; landing of special troops for combat, infiltrating agents into every territories and dropping of weapons etc. The modern man-carrying parachutes are made of nylon and are about 7 to 9 m wide when open. The cargo parachutes may be as wide as 30m when open.

               Now the question arises how does a parachute work?

               A parachute operates on a simple principle involving the force of gravity and air resistance — the two forces that act upon any falling object. The parachutes start falling towards the ground due to the pull of the force of gravity but the speed of the fall is checked substantially due to the resistance of air. At low speeds the pull of gravity is stronger than the resistance of air and at higher speed, the air resistance becomes more. Also, large flat surfaces offer more resistance than sharp surfaces. At a certain point the object reaches a speed called terminal velocity when air resistance and the pull of gravity are evenly balanced and, thereafter, the object starts falling at a constant speed. Therefore, an object shaped like a saucer reaches its constant velocity sooner. So it falls more slowly than one shaped like a needle.

               As soon as the parachute canopy opens fully, the resistance of air slows down the descent of the parachutist so suddenly that he is jerked sharply. Now even parachutes with holes or slots in their canopies have been developed to reduce the force of these opening shocks.

                The parachutes descend at a rate of about 5 m (15 ft) per second or slightly faster. But if dropped from less than 150 m above the ground, it can prove dangerous because this height does not allow the parachutes to open. The parachutists can control the direction of their descent by pulling on the shrouds and other operational devices.

               Nowadays new parachutes have been developed which enable one to escape from supersonic planes. Parachute-jumping has become a popular sport in the United States and Europe. Today there are many clubs who organize national and international jumping events in which parachutists try to land on small targets on the ground.