ELECTRONICS

1. ELECTRONICS

2. Ever wondered why TV, radio and mobile phones are called electronic gadgets…?? Lets find out why is it so..!!

3. The word electronics is derived from the word “ELECTRON” It is the study of electron behaviour and movement. Electronics is a field of physics and engineering dealing with the design and application of devices, usually electronic devices. The operation of these depends upon the emission, behaviour and effects of electrons.

4. The root of electronics-The semiconductors..!! Some substances like germanium and silicon are neither good conductors nor insulators; their conductivity lies in between that of conductors and insulators. Such substances are called semiconductors.

5. Conductivityofsemiconductor The atoms of silicon and germanium have four electrons each in their outermost shell. All these electrons are involved in covalent bonding and are not free. Hence these elements behave like insulators at room temperature. But they exhibit conductivity when a sufficient amount of energy is provided, at room temperature.

6. Formation of holes and charge carriers.. When an electron is removed from a covalent bond, it leaves a vacancy, (equivalent to positive charge). An electron from a neighbouring atom, can drop into this vacancy, leaving the neighbour with a vacancy. In this way, the vacancy usually called a ‘hole’, can move and serve as an additional ‘charge carrier’.

7. Intrinsic semiconductor In a pure semiconductor, holes and electrons are always present in equal numbers and the resulting conductivity is called intrinsic conductivity. Pure semiconductors are called intrinsic semiconductors.

8. If all semiconductors at room temperature are intrinsic materials then how does it have such wide applications..??

9. Doping The conductivity of semiconductors can be increased by adding some impurities, called dopants. These impurities increases the conductivity. Hence this gives rise to Extrinsic semiconductors.

10. Extrinsic semiconductors Extrinsic semiconductors are classified on the basis of the dopants added. Two types of extrinsic semiconductors are p-type and n type. These are used in the manufacturing of wide range of diodes and transistors

11. A closer look at n-type semiconductor When a pentavalent element (antimony, arsenic & phosphorous) is doped with a pure semiconductor it forms an n type semiconductor. It Has 5 valance electrons in the outer most shell, 4out of the 5 contribute in covalent bonding. The 5thelectron Acts as current carriers. The dopant donates electrons to the semiconductor and hence is called donor impurity.

12. A closer look at p-type semiconductor When a trivalentelement (boron, indium, gallium or aluminium) is doped with a pure semiconductor it forms an p type semiconductor. It Has 3 valance electrons in the outer most shell, all 3 contribute in covalent bonding.at the 4th place hole is generated. holes act as current carriers. The dopant accepts electrons to the semiconductor and hence is called acceptor impurity.

13. Application of semiconductors Diodes..!! Transistors..!! Radio..!! Television..!! And many more.....

14. The Donor me..!! Me -The Acceptor ..!!

15. Diodes..?? How are they formed..?? When a donor impurity is added to one side and an acceptor impurity is added to the other side of a pure semi conductor, the first side becomes n-type and the other Side becomes p-type. Thus a p-n junction is formed. This is called a junction diode or a semiconductor diode.

16. Concept of junction potential..!! There will be diffusion of electrons and holes across the boundary in a p-n junction. At equilibrium, a potential difference is established, this potential difference is called junction potential. This stops further flow of charge carriers, unless an external source is applied. The junction potential is 0.7 V for silicon and 0.3 V for germanium.

17. Biasing of the diodes When an external source of e.m.f (of low value) is connected to a p-n junction, it is said to be biased and the applied voltage is called bias voltage. The diodes can be biased in 2 ways: forward biasing reverse biasing

18. Forward biasing of the diode..!! When the positive terminal of a cell (source of e.m.f) is connected to p-side and the negative terminal to the n-side of a p-n junction, it is said to be forward biased. The flow of electrons from n to p and of holes from p to n It constitutes a forward current (of the order of mA) from p to n. The device offers low resistance.

19. Reverse biasing of the diode..!! When the positive terminal of a cell is connected to the n side and the negative terminal to the p side of a p-n junction it is said to be reverse biased. The charge carriers are repelled away from the junction and no current flows through the junction. The device offers high resistance. There will be a small current of the order of A, during reverse bias; this is due to minority charge carriers, electrons in p type and holes in n type regions.

20. Rectifying action The p-n junction allows current to pass through, in one direction only. This action is called rectifying action and the device is called ‘rectifier’. The p side is called anode and the n side is called cathode. The arrow indicates the conventional current flows from p side to the n side

21. See where I am used..!! 1.Diodes are used to convert AC into DC. 2.They are used in voltage regulation systems. 3.Due to their rectifying action and the current detecting capabilities the diodes have a wide range of applications.

22. Birth of transistors..!! The term ‘transistor’ is a shortened form for transfer resistor. It is a three terminal semiconductor device. It is a device which consists of either one p type region sandwiched between two n type regions (npn transistor) Or one n type region sandwiched between two p type regions (pnp transistor). The middle region is called the base and the two end regions are called the emitter and the collector.

23. npn Transistor action

24. pnp Transistor action

25. I am used in… Amplifiers Oscillators Switching circuits

26. Radio communication Radio communication is the process of sending information from one place and receiving it at another place, without using connecting wires. G. Marconi was the first to put it into practice.

27. Radio transmitter Transmission of speech or music over long distances, using radio waves is called radio broadcasting. The audio (sound) information is changed into corresponding electrical signal using a transducer. Transducer is a device that converts information energy to be transmitted into electrical signal. For sound transmission, the transducer is microphone. http://www.youtube.com/watch?v=_4-Sx-T6VBc

28. Radioreceiver Radio signals sent from the transmitter travel through space and are received by the receiver. Radio waves sent by all stations, are received by the antenna of the receiver. http://www.youtube.com/watch?v=ejqPyfvSRpg

29. Television The word television, the combination of two words ‘tele’ and ‘vision’ literally means seeing at a distance. Television broadcasting is the process of transmission of transient visual image of an actual or recorded scene, along with audio signal to a distance using radio waves.

30. Television transmitter and receiver has the same working principle as that of the radio transmitter and receiver respectively.

31. Hope you enjoyed learning the topic..!!