Category Science

How are millions of substances made from only a few elements?

          The number of naturally occurring stable elements on the earth is 92 only. Although scientists have so far discovered 107 elements in all, but 15 of these have been artificially made in the laboratories. These artificial elements are unstable in nature. The atoms of these 92 elements are also of 92 kinds only. Do you know how millions of substances are made from these elements?

          All substances available in the universe are made by the combination of atoms of these 92 elements. The atoms of different elements combine with one another in various proportions and keep on forming countless substances. Some of the important elements are: iron, gold, silver, copper, aluminium, sodium, potassium (metallic elements), oxygen, nitrogen, chlorine, carbon, sulphur (non-metallic elements). All the elements consist of atoms and the atoms of the same elements are alike. Two or more atoms combine with each other to make molecules. For example, two atoms of hydrogen combine with one atom of oxygen to make one molecule of water. Even a very small quantity of water consists of innumerable molecules. Similarly one atom of sodium combines with one atom of chlorine to make one molecule of the common salt sodium chloride. 

 
 
 
 
 
 
 
 
 
 
 

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Which material does not burn in fire easily?

          Whenever any substance is put in to fire it burns and changes into ash. But asbestos is one such material that does not burn in fire. That is why the fire fighters wear clothes made from asbestos when fighting large fires. In fact their clothes, shoes, gloves, helmets etc. are all made from the fibres of this material.

          Asbestos is a Greek word which means ‘inextinguishable’ or ‘unquenchable’. The invention of this material is not new. The Romans used asbestos sheets 2,000 years ago for wrapping dead bodies in order to preserve them.

          This material is obtained from mines. It is formed by the dissociation of olivine. Olivines are the silicates of calcium and magnesium. Due to certain chemical reactions in the mines, olivine changes into fibres of asbestos. Asbestos obtained from mines is first dried and then its fibres are separated with the help of machines. These fibres are woven into threads and ropes which are then used for making clothes, sheets, mats etc.

          Asbestos is a very useful material. It is used for making fire-proof clothes, paper and as heat-insulator in furnaces. It is also used for making fire proof tiles for buildings. In cold countries, water pipes coated with this material which serve as insulators preventing water from freezing in the pipes.

          It is a bad conductor of both heat and electricity and is least affected by acids and alkalies. It does not burn even at a temperature of 2000°C to 3000°C. Some special varieties of asbestos are now available which do not burn even at 5000°C. This variety is used in research laboratories. The most common mineral of asbestos is chrysotile found in Canada and Russia.

          Canada is credited with 75% of the total world production of asbestos. America manufactures maximum number of items from asbestos though the raw material obtained in this country is only 5%. 

How does a pressure cooker work?

          Pressure cooker is a modern kitchen appliance that can cook almost any type of food in a very short time. It also saves a lot of fuel. Moreover, the nutritional constituents of the food are also not spoilt. Do you know how the pressure cooker helps in fast cooking?

          We know that every liquid boils at a definite temperature at the normal atmospheric pressure. This temperature is called the ‘boiling point’ of the liquid. In the case of water it is 100° C. It is observed that with the increase of pressure, the boiling point of the liquid also increases. Similarly reduction in the pressure lowers its boiling point. It is this phenomenon that prompted the invention of pressure cooker. 

          Pressure cooker is essentially a vessel of stainless steel or an alloy of aluminium. It has a lid fitted with a safety valve at its top to let out the steam in order to maintain the internal pressure within the limit the vessel can bear. A rubber ring is fixed at the junction of the vessel and the lid which does not allow the steam to leak out. A thermally insulated handle is attached to the pressure cooker for handling it. The food to be cooked is put in the vessel along with some water and the lid is closed. When the vessel is heated, the steam so formed increases the pressure inside the vessel. As the pressure increases, the boiling point of water also increases and it reaches up to 130°C. This is why food gets cooked quickly inside the pressure cooker. When the steam pressure inside the cooker increases beyond the required pressure, the control valve is automatically lifted up, allowing the excess steam to escape. Thus the pressure inside is regulated and there is no risk of bursting.

          If there is no hissing or whistling after the cooker has been kept on the oven for a sufficient time, the valve should be slightly shaken to see if the hole below is not choked. Before opening the lid the valve should be slightly lifted up with the help of tongs to allow the steam to escape. 

What are radio waves?

          Radio waves belong to the family of electromagnetic waves which owe their existence to moving electrons. The existence of radiowaves was first predicted by James Clerk Maxwell in 1860, but it was not until 1887 that Heinrich Hertz succeeded in producing them experimentally. “Wireless” telegraphy was first demonstrated by Sir Oliver Lodge in 1894 and it was Guglielmo Marconi, the Italian scientist, who could first successfully transmit a long distance transmission in 1900 with the help of radiowaves.

          It is through radio waves only that sound from the broadcasting station is able to reach our radios. Their use is also made to transmit a variety of programmes. Radio waves work as the carriers for communication signals. The message is modulated with radio waves and transmitted with the help of a transmitter. The modulated signal is received by the radio receiver and then decoded. Radio waves were also used to keep in contact with the flying planes. With the help of these waves they are properly guided and controlled during flights thus avoiding accidents.

          Radio waves are in fact invisible electromagnetic waves which travel with the speed of light, i.e. at 300,000 km. per second. Satellites and spacecrafts keep in contact with the earth stations with the help of these waves. Live communication with the satellites and astronauts has become possible only due to radio waves. These waves can travel both through the air and the vacuum. They can even travel in water and underground to a distance of a few metres. Communication is established between the ships with the help of these waves. Every ship is equipped with radio transmitters and receivers.

          To study the radio waves originating from the different heavenly bodies, scientists make use of radio telescopes. With the help of these telescopes, it has now become possible to identify the planets and stars which generate the radio waves.

          Radio waves are also used by police. They have the equipments by which they can send and receive messages from moving vehicles. Fire brigades also use of radio waves while providing help in accidents. These waves are also used to control traffic. Today we have the instruments which can measure the speed of a moving vehicle from the control room itself.

          In a nutshell, we can say that the world has shrunk due to these radio waves. 

Why do stars twinkle?

          We see millions of stars twinkling in the sky during night. They radiate their light in all the directions. Even though they appear very small yet in reality they are very big. Most of the stars are many times bigger than our earth. They look smaller only because of their great distance from the earth. Do you know why the stars twinkle?

          Our earth is surrounded by a thick cover of air known as the atmosphere. There is vacuum beyond the atmosphere. The gases present in the atmosphere are in constant motion. Because of the movement of gases the density of air in the atmosphere is not uniform everywhere. As such the refractive index of air varies from place to place. When the light from a star enters our atmosphere, it gets deviated from its path several times before reaching our eyes because of the changing density and the consequent change in the refractive index of the air.

          The deviation in the path of light in its passage from one medium to another is called ‘refraction’. Because of this refraction, the light reaching our eyes from the star varies. Due to this variation the stars appear to be twinkling.

          Now the question arises: why don’t moon, sun and other planets twinkle like the stars? This is so because compared to the stars, sun, moon and the planets are very near to earth and as such they appear bigger than the stars. Hence the angles subtended by the moon, sun and the planets at our eyes are larger than the angles subtended by the stars. Because of the larger angles, our eyes are not able to detect the deviation in the path of light from the sun, moon and the planets and hence they do not appear to be twinkling. 

How does a microwave oven work?

          Over the years application of modern technology in the domestic sphere has made our lives more comfortable and easier. Washing machines, vacuum cleaners, microwave ovens etc. are a few examples that meet the demands of the modern society of today. The new gifts of technology especially for household use, always generate a curiosity in us about their working principles. Now let us discuss how does a microwave oven work?

          A microwave oven does not have burning flames or red-hot plates like gas and electric cookers. Its operational mechanism is simple. The user puts the food into a metal box and presses a switch. Inside the box, invisible energy rays bombard the food. 

          The oven gets its name from the rays that cook the food – the rays are called microwaves. Microwaves are part of the spectrum of electromagnetic waves which includes light waves and X-rays. They have wavelengths from about 30cms to one millimetre which places them between the shortest radio waves and infra-red waves. One of their properties is to excite molecules, especially in liquids, and make them vibrate and heat up. For this reason, food with a large proportion of water gets cooked very quickly.

          The source of microwaves in the oven is a magnetron. It is a two-electrode valve for generating high-frequency oscillations. Microwaves generated by the magnetron travel down a metal-duct and are scattered around by a metal fan for a more even cooking. The molecules rub against each other and the friction produces heat. The water then gets heated up and consequently the food gets cooked quickly.

          Microwave ovens are a potentially dangerous source of radiation. For this reason the ovens are metal lined and have strong doors. The oven will not function until the doors are closed thus ensuring safety. Most modern ovens contain small computers that automatically cook the food at the appropriate temperature for the right length of time. Microwave ovens are preferred and widely used in restaurants, hotels etc. where quick service is important.