how does a transistor amplify?

Question

please provide a good link which provides a satisfactory explanation if possible

Answer 1

The design of a transistor allows it to function as an amplifier or a switch. This is accomplished by using a small amount of electricity to control a gate on a much larger supply of electricity, much like turning a valve to control a supply of water.

more at:-
http://www.physlink.com/Education/AskExperts/ae430.cfm

Answer 2

Take for example a PNP transistor. It has high input impedence and low output impedence. When you apply a potential first enough to overcome the barrier potential, the fields created at the junctions amplify by a factor called alfa or hfe in commonemitter configurations. It is ultimately the field interactions that creates the amplification.
We learn it as the input p area is highly doped and the output area lesser doped and intemittent areas medial. Doping means impurity added to the silicon or ge materials used. The P area has more holes and the N are ions. When the transistor is biased positive with adequate power supply Vcc there is migration of ions to holes and this recombination effect creates the amplification since there are more holes in the input P region. The power supply is either positive or negative depending on what output we require eithe more than what given by the amplification factor. In dc operation we bias either positive or negative and ac we supply the sinusoid.
If we vision an energy level diagram, the electrons move from a low energy level breaks the barrier poetential layer or depletion layer and enters the high energy level so the amplification.

Answer 3

http://www.satcure-focus.com/tutor/page4.htm

http://library.thinkquest.org/C006224/amplificationhtml.htm

Answer 4

please follow this link think this will be usefull http://en.wikipedia.org