Category Physics

              In 1911, Heike Kamerlingh Onnes, a Dutch Physicist, invented the phenomenon of superconductivity. He observed that at liquid helium temperature (4.2K) the resistance of mercury totally disappeared. He called this dramatic decrease in resistance as the phenomenon of superconductivity. It was also observed that near absolute zero, several other metals suddenly show near zero electrical resistance. For this outstanding discovery Kamerlingh Onnes was awarded the Nobel prize of Physics in 1913.

            The theory of superconductivity was devised in 1957 by J. Bardeen, L.N. Cooper and J.R. Schrieffer. This is known as BCS theory.

                  For the last 45 years, scientists all over the world are busy in searching superconducting materials for room temperature use. Niobium-tin alloy is one material which shows super conduction at 18K. Niobium-germanium is a superconductor at 23K. In 1986, L.X. Mueller developed lanthanum-barium which is superconductor at 35K. In 1987, Ching Wu Chu developed Yttrium barium and copper with a transition temperature of 94K. In India many research laboratories such as NPL, TIFR, Saha Institute of Nuclear Physics etc. are carrying out research in the field of superconductivity.

Continue reading “What is Superconductivity?”

             The telephone is a device by which we can talk to our friends and relatives living in other cities or countries even. It is being used everywhere, in business, offices, homes and factories.

              The world ‘telephone’ has been derived from the Greek words ‘tele’ meaning far and ‘phone’ meaning sound. Thus, the word ‘telephone’ means the device which takes the sound to faraway places. The story of its invention is very interesting. It goes back to June 2, 1875, when Alexander Graham Bell was working along with his assistant Thomas Watson on some problem related to telegraphy. Bell was on the telegraphic receiver in one room, whereas his assistant was in another room. Watson created some vibrations on an iron strip. Bell rushed to the other room and found that the iron strip vibrating between the poles of a magnet was producing electric current in the connecting wire. It was this historic observation which led to the birth of telephone. He was able to demonstrate the telephonic conversation on March 10, 1876.

                Do you know how the telephone works? It has two main parts: the mouthpiece and the earpiece. The mouthpiece of the telephone works as a transmitter whereas the earpiece works as a receiver. Both are enclosed in one cage and are connected by the line wire. When we speak into the mouthpiece, a diaphragm attached to it starts vibrating. And in accordance to these vibrations a varying current is produced. This current is carried by the telephone line wire to the receiver of another telephone. This varying current produces vibrations in the diaphragm attached to the receiver which is then converted into original sound waves. The person at the other end hears clearly the voice of the speaker. The same process is repeated between our receiver and the mouthpiece of the telephone at the other end. In this way two persons can talk to each other on the telephone.

              Today, every country has a vast network of telephone lines. Thus world has become very small. Thanks to the telephones!

              A transistor is a tiny solid state device used to control and amplify an electric signal. Transistors are now used in place of vacuum tubes in many electronic circuits. Transistors are smaller, weigh less, last longer and are less expensive than vacuum tubes. They consume less electricity and produce less heat than vacuum tubes.

             Transistor was first developed in 1948 by three American Physicists, John Bardeen, William Shockley and Walter Brattain. These three won the Nobel Prize for physics in 1956. The development of transistor revolutionized the world of electronics.

                  A transistor is made of a semiconductor such as silicon or germanium with certain amount of impurities doped in them. When impurities of V A group like arsenic or phosphorus are doped in the semiconductor material, it becomes a n-type semiconductor (n-for the negatively-charged electrons). On the other hand, if III A group elements like Aluminium are doped, it becomes a p-type semiconductor (p-for positively-charged holes). 

              Transistors are of two types-junction and field effect. Junction transistors are again of two types npn and pnp. In an npn transistor, the middle layer is p-type while the two outer layers are both n-type. The middle layer is the base, one outside layer is the emitter and the other outside layer is the collector.

              Another type of junction transistor is pnp transistor which contains a layer of n-type semiconductor sand witched between two layers of p-type semiconductor. In the pnp transistor, the positively charged holes move from emitter to collector.

             In a field effect transistor, there are only two layers of semiconductor. The current flowing through one of the layers, the channel, is controlled by a voltage connected to the other layer, the gate.

             Transistors are used in computers, stereos, radios, televisions, satellites and many other electronic circuits.