Category Physics

Why are fireworks colourful?

                Fireworks (crackers etc.) are used on various occasions of national, religious and social festivals in almost all the countries of the world. It is estimated that every year a sum of Rs. 5000 crores is spent all over the world on fireworks of about 300 varieties. When they are ignited, they explode and present a riot of colours. Do you know why they are so colourful?

              Fireworks are prepared by a mixture of potassium nitrate, sulphur, coal and salts of certain metals. The colour is provided by salts of metals like strontium, barium, magnesium and sodium. They are mixed with potassium chlorate. Barium salts give out green colour, while strontium sulphate produces light sky blue colour. Strontium carbonate produces yellow colour whereas strontium nitrate produces red, salts of sodium impart yellow colour, those of copper impart blue colour. Aluminium powder in the fireworks produces the silvery rain. When fireworks explode these salts burn in fireworks, various colours come out and present a spectacular sight.

                    China was the first country to manufacture fireworks.

                    Hundreds of years later, Europe, Arabia and Greece also manufactured them. At present, a small town in India named Shivkashi manufactures the largest amount of fireworks in the country.

                    Some time ago, in a celebration in Japan, colourful fireworks were lighted that went up to a height of 915 metres and were scattered in a radius of 305 metres. 

What is echo?

            When we speak loudly in a big empty hall or in a temple, we hear our own sound repeatedly. This is called echo. An echo can also be heard by shouting near a deep ditch or a well. The thunder of clouds is another example of echo.

             We know that sound travels from one place to another in the form of waves. The velocity of sound in the air is 340 metres per second. When we speak, the sound waves emanating from our mouth spread out in all the directions. When these waves meet a wall or some other obstacle in their way, they are reflected back. These reflected waves are heard by us as an echo. Hence echo is produced when sound waves are reflected by some obstacle. But all objects do not reflect sound. There are some objects like wood, jute, cardboard etc. which absorb sound.

              To hear an echo, it is essential that the obstacle reflecting the sound waves must be situated at least at a distance of more than 17 metres from us. This is because the effect of sound persists on our ears for one-tenth of a second. If one sound signal has reached the ears and within one tenth of a second another sound signal reaches our ears, it will not be distinguished because during this period the effect of the earlier sound is persisting in the ear. Sound travels about 34 metres in one-tenth of a second. As such, if the object reflecting the sound waves is situated 17 metres away from the speaker, the time taken for the sound to travel this distance from the speaker’s mouth to the object and back to him would be one-tenth of a second and the reflected sound can be distinguished by our ear as an echo.

              In Modern buildings architects use methods and materials which reduce echoes and favour good sound transmission. Auditoriums are built with rounded corners and few large flat surfaces. This prevents sound-waves from being reflected to any one position. They are scattered in many directions and the only sounds heard are those sent out from the source. Some fibre-boards having many holes are used for making rooms sound-proof. By the use of these materials the sound-waves are either absorbed or scattered so that production of echo is reduced. Radars and sonars work on the principle of echo. 

 

Why does the rising and setting Sun appear red?

When the sun rises in the east, it appears like a red ball. As the day advances, its colour appears white, but again at the time of sunset in the evening, it appears red. Do you know why it is so?

We know that our earth is surrounded by the blanket of air called atmosphere. Sunlight passes through the atmosphere before it reaches us. We also know that sun light is composed of seven colours – Violet, Indigo, Blue, Green, Yellow, Orange and Red. In the mornings and evenings, when the sun is near the horizon, the rays have to travel about fifty time’s longer path in the atmosphere to reach us than it does in the noon. The dust, smoke and water vapour present in the atmosphere scatter away these colours differently. Violet, indigo and blue are scattered most and red and orange are scattered least. That is why most of these two colours reach our eyes. As a result, the rising and setting sun appears red. 

 

How are the Pearls formed?

  Pure pearls are very precious. You will be surprised to know that only a small sea-creature, oyster makes them. An oyster can crawl on the ground also. The biggest tragedy with this little creature is that fish of the sea or the bigger members of its own family eat it away. When the oyster comes to the sea-shore to save its life, man eats it. In order to protect itself, it forms a hard shell around its body with a unique substance called ‘nacre’ or mother of Pearl. Pearls are made within this hard cover.

             The discovery of pearls is an interesting story. Some four thousand years ago, a Chinese was suffering from hunger. To satiate his hunger he opened some oysters to eat. Inside one oyster he found one small round shining ball. The shinning ball-like thing was later on called pearl.

              Whenever, by chance, a sand particle goes inside the shell of an oyster and rubs against the animal’s tender body in order to soothe this irritation, it starts depositing layers upon layers of the shell material on this particle. These layers are made up of calcium carbonate. After sometime the formation of the pearl inside the shell is completed. The pearl so formed is round, white and shining. This is called pure pearl. However, the pearls are not essentially white only. Their colours may be black, white, rose, pale blue, yellow, and green, mauve also.

                Man has now developed some techniques of making artificial pearls. Under these techniques sand particles are introduced inside the shell. After two or three years, when the shell is taken out of water, a pearl is found inside it. These pearls are called cultured pearls. Japan has perfected the technique of making beautiful cultured pearls. Since pure natural pearls are very costly, generally we purchase pearls developed by these artificial techniques. On the 7th May, 1934, a pearl was found in Philippines measuring 23 cm with a diameter of 13 cm. This pearl weighed about 6.37 kg. This pearl was called Pearl of Laozi. 

What is Plastic Surgery?

              Plastic surgery is a branch of surgery devoted to restoration, repair and correction of malformations of tissues. It concerns not only return to normal appearance but also the restoration of function. The field of plastic surgery has several sub-divisions such as cosmetic surgery, management of congenital defects, burns, wounds and other acquired defects.

             Cosmetic surgery deals with improving the appearance of tissues or organs such as the nose, face, eyes or breasts. The most common types of cosmetic surgery are face lift to remove wrinkles from the face and neck and a rhinoplasty to change the shape of the nose.

             Plastic surgeons treat physical defects that exist since birth (congenital defects) or are caused by injury or disease. Often the body part that is defective or damaged does not work as it should. In such cases, the surgeon does reconstructive plastic surgery. This often requires grafting. In grafting skin muscle, bone or cartilage is transplanted from a healthy part of the body to the hurt or damaged part. Sometimes reconstructive surgery involves reattaching several limbs, rebuilding damaged tissues, restoring damaged blood vessels and nerves. Plastic surgeons are available almost in all the hospitals.

             Plastic surgery has been practiced for hundreds of years in China and India. Chinese and Indian doctors were reshaping noses and lips long ago.

 

What are different types of telescopes?

            A telescope is an optical instrument used to see distant objects clearly and magnified. The telescope was invented in 1608 by a Dutch optician Hans Lippershey. In 1609, the Italian astronomer Galileo made his first telescope and observed the rings of Saturn and Jupiter’s moons. Today there are three main kinds of telescopes: refracting telescopes, reflecting telescopes and radio telescopes.

Refracting Telescopes: A refracting telescope makes use of two lenses fitted at the end of a tube. An astronomical telescope consists of one larger size convex objective lens and a convex eyepiece while a Galilean telescope makes use of a convex objective lens and a concave eyepiece. Modern refracting telescopes usually contain complicated lens systems to correct chromatic aberrations.

Reflecting Telescope: A reflecting telescope is made of a concave mirror that gathers and focuses light waves. Another mirror near the point where waves come together reflects light into the eyepiece.

            A Newtonian telescope uses a mirror set at a 45° angle to reflect the light into the eyepiece. A Casegranian telescope has convex mirror which reflects light through a tiny hole in the centre of the objective mirror. The light passes through to the eyepiece, which makes the image larger.

           The largest reflecting telescope in the world is at the Yerkes observatory in Wisconsin. Its objective lens has a 102cm diameter. The Palomar observatory in California has a reflecting mirror with a diameter of 508cm.

Radio Telescopes: A radio telescope has a huge reflector shaped like a bowl which reflects radio waves to a detector. Radio telescopes are used in astronomy. These telescopes can be used under all weather conditions.