Category Science

What is meant by acoustics?

            Acoustics is the branch of science that deals with the production, control, transmission, reception and effects of sound.

            The word ‘acoustics’ has come from the Greek term akoustikos, meaning ‘for hearing’.

            Let’s see why acoustics is relevant. When a concert hall or a theatre is built, the architect needs to plan how sound waves travel through the air, so as to make sure everyone hears the same sound, clearly.

            Here, sound may be balanced using soft absorbent materials like curtains, carpets, plaster etc. Next, take the case of a doctor. He uses high pitched ultrasound waves in order to see the interiors of the human body.

            The wonders of acoustics have been seen in the world since centuries. The Greeks were known to be one of the earliest users of this technology.

            Today, there are many examples that demonstrate acoustics. One such is the Sydney Opera House in Australia.

How is the altitude of a flying airplane determined?

            While travelling in a plane, have you ever looked down and wondered why everything on the earth looked so small? The reason is that planes fly at great heights. The greater the height, the smaller will be the appearance of the objects on the earth. The height of the plane is measured by an instrument called the altimeter. 

            There are five main types of altimeters. The first is the pressure altimeter. It basically measures the decrease in air pressure as the altitude increases. The second is the radio altimeter. This is used to measure the time required by a radio pulse to travel from the airplane to the ground and back, much like radar. The third type is the sonic altimeter which makes use of sound waves. The fourth type measures the altitude by using the effect of atmospheric pressure on the boiling point of a liquid. The fifth type is the capacitance altimeter. 

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What is a sextant?

          The word sextant comes from the Latin word “sextus” which means one-sixth. The sextant is an instrument used for measuring angles, primarily altitudes of celestial bodies like the sun or a star. It is also used in navigating ships and planes to determine the latitude. The height of the tall buildings and pillars can also be measured with the help of a sextant.

       Sextant was invented by an Englishman, John Hadley in 1731. The device consists of an arc of a circle, which is usually one-sixth of a circle or 60 degrees, and a movable radial arm pivoted at the centre. A movable mirror is fixed at the end of the arm. The other end extends to the scale. A telescope is mounted on the sextant, and a glass mirror is mounted in front of the telescope.

          To operate the sextant, the operator looks through the telescope straight at the horizon. Moving the mirror, the sun or any particular star is made to appear exactly on the horizon. The arm which moves the mirrors gives the required measurement of the angle. From this angle and the exact time of the day, the latitude is determined by means of published tables.

          The invention of sextant has laid the foundation of modern navigation.

Which is the Land of Midnight Sun?

          The land of the midnight sun is the popular name of the Scandinavian country of Norway, where from mid-May till the end of July, the sun doesn’t set completely. As a result, there is a long twilight, instead of night during this period. On its northernmost tip, the sun never sets completely for about two months in the summer, but at the same time there is no sun for two months in the winter.

          The midnight sun is seen in the Polar Regions when the sun appears above the horizon at midnight. Due to the tilt of the earth’s axis to the plane of its orbit by 23.5 degrees, each hemisphere is inclined towards the sun during the summer and away from it during winter. Due to this, the Arctic and Antarctic regions see the midnight sun for some time each year. When there is winter in the Antarctic region, day is indistinguishable from night. The sun does not rise and there is total darkness in the Antarctic Circle.

          At this time (April to July) the Arctic Circle enjoys summer with the sun visible for 24 hours a day. The sun rises in the sky and moves very slowly. Towards evening, it begins to set, until it reaches the horizon. Then it begins to climb again. At the Arctic Circle, this continues for about two months, but the actual midnight occurs on June 21.

          After six months, the Arctic region plunges into darkness and the Antarctic Circle is bathed in sunlight. Midnight Sun occurs in Antarctic from mid-November to the end of January.

          Extreme northern latitudes are sometimes called the ‘Lands of the Midnight Sun’. The Midnight Sun can also be seen near Bylot, an island of northern Canada. Every year thousands of tourists flock here to see one of the most impressive and extraordinary sights — the midnight sun. 

What is Ionosphere?

          The story of the discovery of the Ionosphere is very interesting. On December 12, 1901, G. Marconi demonstrated with his newly discovered wireless equipment that radio waves could travel across the Atlantic Ocean. This demonstration could not be explained with radio waves travelling in straight lines over the spherical shaped earth for such a long distance. So the scientists came to believe in the existence of some layer in the upper atmosphere, which acts like a mirror for radio waves and reflects them.

          In 1902, O Heaviside of England and A.E. Kennelly of the United States confirmed the existence of such a layer. This was called Heaviside-Kennelly layer. Watson Watt, the inventor of radar, coined the name ionosphere to this layer. Later in 1925, E.V. Appleton and M.A.F. Barnett of England experimentally proved the existence of the ionosphere.

          How did the ionosphere come into existence?

 

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Why does the Mediterranean Sea appear blue and the Atlantic Ocean green?

            Do you know that about 3/4 of the earth’s surface is covered with water? There are three main oceans: The Atlantic, the Pacific and the Indian Ocean. The Arctic Ocean is taken to be a part of the Atlantic Ocean, and the Antarctic Ocean is made up of the southern parts of other oceans.

            The Atlantic Ocean is a great mass of water that separates Europe and Africa, from the American continent. It is shaped like an hour glass, with a ‘waist’ where Africa and South America bulge out towards each other. Although in area it is less than half of the Pacific Ocean, it has many ‘Secondary’ water bodies, such as the Arctic Ocean and the Mediterranean Sea.

            The Mediterranean Sea lies between Southern Europe, Africa and. South-West Asia. It is linked to the Atlantic Ocean through the narrow strait of Gibraltar in the west and to the Black sea in the north-east by the Sea of Marmara.

            One of the surprising facts about the Mediterranean Sea and the Atlantic Ocean is that while the water of the former appears blue, that of the latter appears green! Can you guess why this happens?

            The varying colours of the Mediterranean Sea and the Atlantic Ocean depend mainly on the amount of sunlight scattered from their surface. The colour of the scattered sunlight depends upon the substances dissolved in sea water. Generally, of the seven colours of the sunlight blue is scattered most. That is why most oceans appear blue. However, in the case of the Atlantic Ocean, the green effect is produced by the decaying plants in the ocean bed. When these plants decay, yellow pigments are released which get dissolved in the water. The water now scatters both blue and yellow light, and the resulting mixture produces the characteristic green shade.