My Science School

           Cosmic rays are streams of high-energy charged tiny particles that constantly enter the atmosphere of the Earth from outer space. They consist mainly of 89% protons, 9% radiations and 2% of heavy nuclei of carbon, nitrogen, oxygen and iron. These are called primary cosmic rays. They travel nearly at the speed of light.

          When these tiny particles of primary cosmic rays collide with the nuclei of the air, they produce new particles called secondary cosmic rays. Secondary cosmic ray particles also travel at high speeds. They further collide with other atoms and again create new particles. After several collisions on the way, only very few secondary cosmic ray particles are able to reach the surface of the Earth. Secondary cosmic rays consist mainly of positrons; neutrons, mesons and neutrinos. All these particles are called elementary or fundamental particles.

          Where do these cosmic rays originate in space? It is believed that most of the cosmic rays originate in the supernova explosions far beyond our Milky Way and some of them are produced by storms on the Sun and stars of the galaxy. More and more information is being gathered about the origin of these rays.

          The small amount of radiation caused by cosmic rays is not enough to harm the Earth. They can do little damage to the human body. These rays have been colliding with the Earth for billions of years and life has been least affected by them. So, it is believed that cosmic rays are harmless. However, there is a possibility that cosmic rays may have a harmful effect on astronauts because the intensity of cosmic rays is far greater in space than on the Earth.

 

          There was a time when man used to communicate by beating drums or burning fires. Those days, in the absence of any scientific knowledge, it was extremely difficult to send messages to distant places. Today, we have different means of communication like the telephone, radio, television and the press. Now scientists have added artificial communication satellites or comsats to send telephone, radio, telex, fax messages and television signals around the world.

          An artificial satellite is a man-made Moon that orbits around the Earth. With the help of rockets, they are launched into geostationary orbits. This means that they are placed in fixed orbits over the equator about 36,000 km high where they orbit the Earth in exactly 24 hours. Because of this they appear to remain stationary in the sky from the Earth. Artificial satellites are of many different shapes and sizes and are sent into orbit for several different reasons. They usually have solar cells which convert the energy of the Sun into electricity which is used to run the satellite instruments. 

          Communication satellites pick up the signals transmitted from a point on the Earth and relay them to the other side of the world by amplifying them and then beaming them down to a ground station. Communication satellites have different channels for telephone, radio and television signals. The signal is first sent to the satellite with the help of high-frequency microwaves. This is received by the antenna fitted in the satellite. After amplifying, it is transmitted by a transmitter. Its power is increased by a transponder. The signal is received by the earth station. This is how a signal travels thousands of kilometres. If a message is sent through conventional methods, very long cables are required. Today, telephone messages between several countries are exchanged through satellites.

 

Continue reading "What are communication satellites? "

For many centuries man had been dreaming of space travel and exploration of extra-terrestrial lands. The first concrete step in this direction was taken by the Russians when they launched the artificial satellite Sputnik I on 4 October, 1957. A month later on 3 November, 1957 a bigger Sputnik II was sent into the space. It took along, the first living creature, a dog named Liaka. Following closely on the heels of the Russians, the United States launched its first satellite Explorer I, on 31 January, 1958 triggering off a race between the two countries in space research. The first man in space was a Soviet cosmonaut, Yuri Gagarin, who orbited the earth on 12 April, 1961 in Vostok I.

In 1961, America started the famous Apollo project which was aimed at taking man to the Moon. It was an ambitious project with hurdles at every step. On 27 January, 1967 the Apollo project had a serious setback. During a practice session the astronauts Virgil Grissom, Edward White and Roger Chaffee were burnt to death in a fire aboard the spacecraft. This tragedy led to many modifications in the design of the spacecraft.

In July 1969, Neil Armstrong, Edwin Aldrin and Michael Collins went to the Moon in Apollo - 11. On 20 July, 1969 at 10.56 p.m. (GMT) Neil Armstrong put his first step on the surface of the Moon. He sent the message to the Earth, ‘That’s one small step for a man, one giant leap for mankind’. A little later, Aldrin also landed on the Moon. Michael Collins remained in the spacecraft. Armstrong and Aldrin stayed on the Moon for 21 hours and 35 minutes.

After this, four successful landings of the Apollo on the Moon followed. The final landing was on 11 December, 1972 by Apollo 17. Eugene Cernan and Harrison Schmitt spent 74 hours and 59 minutes on the moon and returned with 113.6 kg of lunar material. The first Indian to go to the space was Sq. Ldr. Rakesh Sharma in a joint Indo-Soviet flight on 3 April, 1984.

So far a total of 12 Americans walked on the Moon during the Apollo programme, bringing back 380 kg of rocks and soil. They have moved about 100 km of the lunar surface in a total time of 166 hours. 

          A tape recorder is a machine that records sound waves into a magnetic pattern on a tape. When the pattern played back reproduces the original sound.

          A person whose voice is to be recorded is asked to speak before a microphone which converts the sound into an electric current. Since this current is very weak, it is amplified by an amplifier. The current is then passed through the recording head of the tape recorder. A current passing through the coil produces a magnetic field. Since the current is alternating in nature, so it produces a varying magnetic field. During the recording, the tape moves past the recording head. The plastic tape is coated with a magnetic substance like iron oxide and so, it is called a magnetic tape. The varying magnetic field in the recording head which is in accordance to the sound produces a magnetic pattern on the tape.

          This is how the sound is recorded on the tape in the form of a magnetic pattern.

          The tape can be played back over and over again. To play back the tape, it is again fed past the recording head. This head now acts as the playback head. As the tape moves, its magnetic pattern causes the current to flow through the coil in the head. As the magnetic field on the tape varies, the current in the coil also varies. The current is then amplified by an amplifier and fed to a loud speaker. The loud speaker changes the current into the original sound and thus we listen to the recorded voice.

          The sound recorded on a tape can be erased by an erasing head.

          The recording described above is called single track recording. Nowadays two or four track recorders are available which produce stereophonic sounds.

          In the last few years, cassette tape recorders have become very popular. The reel of the tape and the take-up reel are both held in a plastic case called a cassette. To record or play back, the cassette is simply placed in the record player and the correct switch is pressed.