Category Science & Technology

What is a prime number?

          Any positive integer which is greater  than one and divisible by only itself is called a prime number. For example 2,3,5,7,11,13,17,19,23,29, etc. are all prime number – numbers that cannot be split by division by any other number except 1 and the particular number itself.

          The prime numbers lie at the very roots of arithmetic and have always fascinated those dealing with figures. We can take the sequence of the above given series of prime numbers as far as we like, but we will never find a prime number divisible by another. Over the centuries, the world’s greatest mathematicians have tried to do so and always fail, although they have also been unable to prove that no such number exists.

          Every positive integer greater than one can be expressed as the product of only a single set of prime numbers. Despite the fact that prime numbers have been recognized since at least 300 B.C. when they were first studied by the Greek mathematician Euclid and Eratosthenes. Still these numbers have not yet unfolded certain mysteries relating to them.

          There is infinity of prime numbers and in theory anything may happen in infinity. But so far theorists have not been able to even find any particular rule or theory governing the gaps between prime numbers, which still remains a great mathematical mystery.

          However, the highest known prime number was discovered in 1992 by analysts at AEA Technology’s Harwell Laboratory, Oxon. The number contains 227832 digits, enough to fill over 10 fullscap pages. 

What is Electricity?

               In ancient times, man had no idea of electrical energy. They took the flash of lightning during a thunder storm to be a signal for an impending destruction from the heavenly Gods. With the passage of time, science in its own way explained the mystery of this great energy called electricity.

               Today, we cannot imagine the normal life without electricity. Commonly we know it as a form of energy, that powers almost all machines or mechanical devices — trains, radios, television sets, freezers and so on. Electricity is a phenomenon involving electrical charges and their effects, when at rest as well as when in motion.

               Electricity that we use flows through wires as electric current. In a nutshell, when an electric current flows through a conductor of finite resistance, the heat energy is continuously generated at the expense of electrical energy. The particles of a matter may be positive, negative or neutral. We know that electricity has its two important particles — protons and electrons. Electron is negatively charged while proton is charged positively to an equal extent. The object containing an equal number of protons and electrons is electrically neutral. For example, anode is a positive electrode while cathode is a negative one. Bulk of the electricity we use is produced in power stations. In the generator of a power station, coils of wire are made to rotate between powerful magnets in order to rotate electric current through the coils. Electricity travels through substances like copper, aluminium and iron. These are called conductors. However, electricity cannot pass through some materials like rubber and glass and these are called insulators. 

               Electricity which flows in one direction and then in the opposite is called Alternate Current (A.C.). Each movement of A.C., back and forth, happens very quickly – about 50 times a second. The electricity that flows in our houses is mostly A.C. Steady flowing current in one direction only is known as Direct Current (D.C.). For instance, battery current is D.C.

               Soon after the invention of electric cell by Alessandro Volta, people came to know that heat, light, chemical reactions and magnetic effects could be produced from electricity.

               As early as 600 B.C. Greeks discovered electricity by rubbing Amber with cloth which enabled it to attract small pieces of papers. In fact, the word electric originated from the Greek word Electron. Based on the theory of “Electro-Magnetic Induction” of Michael Faraday in 1831, first successful generator or Dynamo was made in Germany in 1867. USA produced; electricity by running turbines with the help of falling water in 1858.

               Subsequently hydel and thermal power stations came into existence all over the world. During the 20th century many nuclear power stations were established to meet the growing demand of electricity. 

What is a pyrometer?

          A pyrometer is an instrument used for measuring high temperature – especially those which can’t be measured through ordinary thermometers. For example, pyrometers are used to measure temperature in a furnace. 

          There are two main kinds of pyrometers: the radiation pyrometer and the optical pyrometer. In a radiation pyrometer, the radiation from the hot object is focussed onto a thermopile which is a collection of thermocouples. When the thermopile gets heated due to the intercepted radiation, it produces a voltage. The amount of voltage developed depends upon the temperature. Proper calibration permits this electrical voltage to be converted into the temperature of the hot object.

          Sometimes a bolometer is used instead of a thermopile. A bolometer has two strips of the platinum metal. When the platinum strips heat up, the electrical resistance of the strips changes. The change of resistance can be used to measure the temperature. 

Continue reading “What is a pyrometer?”

What is solar wind?

            The solar wind is the constant flow of charged particles from the sun. These particles include protons, electrons and some nuclei of heavy elements. They are accelerated by high temperatures of the solar corona or outer region of the sun, to velocities high enough to allow them to escape from the sun’s gravitational field. Recent researches using satellites have shown that the solar winis made up of plasma, i.e. ionized gas, mostly hydrogen and helium, containing nearly an equal number of protons and electrons.

            The solar wind streams from the sun though outer space at a speed of about 480 km (300 miles) per second. It takes the particles about 3 days to reach Earth.

            In 1958, the American physicist, Egune Norman Parker, called this outward system of protons — the solar wind.

            The solar wind causes the tails of comets to change direction and point away from the sun. It also causes magnetic storms which may disrupt radio communications on Earth. The solar wind causes ionization of the gases in an upper atmosphere, resulting in the coloured light phenomena known as auroras.

            When the solar wind encounters Earth’s magnetic field a shock wave results, the nature of which is not fully understood. That part of the solar wind which does not interact with Earth or the other planets continues to travel at supersonic speeds upto a distance of approximately 20 astronomical units (one astronomical unit is about 1.5 x  kms). As it passes through a similar shock phenomenon it loses this supersonic characteristic. Here the gas cools off and eventually diffuses into the galactic space.

 

 

What are Novae and Supernovae?

               Some stars that have been shining steadily for millions of years suddenly undergo a fantastic change. This change comes in a very unpredictable and violent way. Within a few hours or a couple of days their brightness increases by 10,000 times or more. An ordinary observer might think that a new bright star has appeared in the sky. The increase in brightness occurs when an explosion throws up a small amount of the star’s matter—probably less than a hundred thousandth of its matter. This matter is actually a shell of gas that expands brilliantly in the outer space as soon as the ignition and explosion take place. A nova reaches its maximum brilliance in a few hours or a few days, and then after a few weeks or months it returns to its normal brightness. The decline of the brightness begins at various rates which often fluctuate. After a few years the brightness of the novae remnant becomes steady and a gas cloud may be observed around it which expands at a rate of hundred kilometres per second. Some novae have been known to erupt more than once and are termed as recurrent. All recurrent novae flare up at long intervals. About 20 or 30 novae are believed to occur in our galaxy every year. 

               It has been found that the novae reach absolute visual luminosities to the extent of about 10,000 to 1,000,000 times than that of the sun. The total energy emitted during a large novae outburst is of the order of  ergs, equal to the radiation from the sun in 10,000 years. Should the sun ever become novae, the earth would be destroyed in a few hours or days. However, Sun is unlikely to become so.

               A supernova is a much more spectacular event than a nova. In a supernova explosion, there is a complete self-destruction of the star or at least one-tenth of its matter is thrown off. This may result in an increase in brightness which reveals an entire galaxy as the increase is a billion times more.

               The remains of a supernova that occurred in 1054 A.D is still seen today as the crab nebula which has become one of the most fascinating objects in the sky. Some supernovae including the above were bright enough to be seen in the broad daylight. It seems that a supernova occurs once in about every 300 years. All supernovae are shattered to pieces in their explosions, collapsing into neutron stars.

 

How does a jet engine work?

          ‘Every action has an equal and opposite reaction’ – Newton enunciated this principle long ago which is commonly known as Newton’s third law of motion. And a jet engine works on this principle. Its working can be compared to the action of a swimmer who swims forward by pushing water backwards. To put it in the Newtonian law, here the action is pushing of the water backwards and the opposite reaction is the forward movement of the swimmer. In a similar fashion a jet engine ejects (pushes backward) gases at the rear with a great speed and the resulting opposite reaction to this action is the moving of the aircraft in the forward direction in an equal speed. But where does this gas come from and how is it released with such a great force?

          All jet engines have fuel inside them which when burnt in the engine produces a great amount of hot gases almost instantly. It is like an explosion. These hot gases blast out of the back with a great force and the engine reacts by being pushed forward with an equal force. This forward force is called thrust. To get an idea of this movement, we can observe the motion of an air-filled balloon when the air is released suddenly. The balloon zips away rushing out the air in one direction. The rushing out of air is responsible for pushing the balloon in the opposite direction with a thrust.

          The rockets also work on the same principle. The main difference between jets and rockets is the source of oxygen to burn the fuel. A jet engine takes in oxygen from the air around it through an intake nozzle. But a rocket carries its own oxygen which may be in the form of Liquid oxygen in a tank or may be part of a solid fuel the rocket burns. The jet engines have compressors to compress or squeeze the sucked air together before it is mixed up with the fuel and burned in the combustion chamber thereafter. The compression is done to increase the force of explosion within the engine.

 

Continue reading “How does a jet engine work?”