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Tuesday, 20 March 2012


Electronics is concerned with the movement with electrons.Circuits are complete pathway of electrons to travel along while they do useful works.This works ranges from lighting a torch bulb to running a huge computer .These pathways are connected to varous electrical components that each perform different functions .Its components include valves ,transistor,resistors ,capacitor and inductors.
The diode valve invented by Jonh Fleming in 1904. It consist of two electrodes , a cathode and an anode, in a sealed glass tube from which the air has been removed .It can convert alternating current (AC) to direct current (DC) . When the cathode is heated ,electrons are emitted .These are attracted towards the posively charged anode .A current therefore flows through the valve ,but only in one direction- towards the positive anode.If the anode becomes negatively chraged, no current flows.
The triode valve has an anode , a cathode and and a third electrodes called the grid. The flow of electron from cathode to anode is effected by the charge on the grid . As the grid becomes more positive a greater number of electrons floe through it.The voltage on the grid therefore controls and can also increase (amplify) the currentflowing from cathode to anode.
during the middle of the 20 th century scientist found that the flow of electricity through certain solid materials called semiconductors could be controlled without using a vacuum.The solid material ,germanium or silicon.Is made very pure .Then carfully controlled amounts of Boron ,Arsenic, Phosphorous or Indium are added.The silicon is now doped.These
impurities alter the way that the current flows through the solid.

These solid devices called transistors quickly replaced valves in many circuits.Unlike valves they require no heaters,are small and need much less voltage to run them. Because they are so small they are put in containers to protect them .These containers are made of plastic or metal.
Gradually transistors were made smaller and cheaper .soon several were packaged together to amke a chip.
The next development was to put a complete circuit on a chips. This is called an intigrated circuit. Intigrated circuit are light,long lasting cheap and reliable.

In order to make a chip , the circuit is first drawn on a very large scale with the help of computers it is then reduced and etched on to a slice of silicon .The chips are  then tested  this is done using very fine probes under a microscope. After testing the chips are put into their containers.

The chip is connected by wires of very thin gold or aluminium to pads around it .These pads are joined to the connectors or pins of the container. They are now readly for use.

Calculators were one of the first products to use silicon chips.Now intigrated circuits are used in numerous devices, including amny household appliances. 

Wire-wound resistors and the colour-code.A resistor controls the amount of current in a circuit.It is made of a material that slows down the flow of electrons.When you  turn down your radio you increase the resistance and the signal to the loudspeaker becomes weaker.

A coil or inductor consists of wire wrapped round a piece metal or non-metal. It produces electromagnetic inductance.It has many uses such as smoothing out the ripples of current from a diode valve that has changed alternating current (AC)
to direct current (DC).

A transistor consists of a sandwich of semiconductor material .There are two types of semiconductor. The n-type will produce a flow of electrons from negative to piositive. The p-type will produce a movement of gaps in the electron structure from posistive to negative . Transistors can have an n-type base with a p-type emitter and collector , vice-versa.

An integrated circuit .Transistor and other electrical components. can now be made extremely small. Thousands of components. Forming many hundreds of circuits. Can be permanently  fixed onto a tiny piece of a semiconductor material.This is called an integrated circuit.It is very light , long lasting and cheapand is therefore widely used.
Silicon chips are so tiny that several of them together are still smaller than a postage stamp.

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