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Summing up, in an NPN transistor, a small flow of electrons from emitter (E) to base (B) allows a much larger flow of electrons from emitter (E) to collector (C). Given that conventional current (flowing from + to - ) is in the opposite direction to electron flow, we say that a small conventional current from base to emitter allows a large current to flow from collector to emitter.

A PNP transistor works the other way. A small conventional current from emitter to base allows a much larger conventional current to flow from emitter to collector. The operation is more complicated to explain since the principal charge carrier in a PNP transistor is not the electron but the `hole'.

The operation of NPN and PNP transistors (in terms of conventional currents) is summarized in [link] .

An overview of bipolar transistors as current amplifiers. (Left) An NPN transistor. (Right) A PNP transistor.

Interesting fact

The transistor is considered by many to be one of the greatest discoveries or inventions in modern history, ranking with banking and the printing press. Key to the importance of the transistor in modern society is its ability to be produced in huge numbers using simple techniques, resulting in vanishingly small prices. Computer “chips” consist of millions of transistors and sell for Rands, with per-transistor costs in the thousandths-of-cents. The low cost has meant that the transistor has become an almost universal tool for non-mechanical tasks. Whereas a common device, say a refrigerator, would have used a mechanical device for control, today it is often less expensive to simply use a few million transistors and the appropriate computer program to carry out the same task through "brute force". Today transistors have replaced almost all electromechanical devices, most simple feedback systems, and appear in huge numbers in everything from computers to cars.

Interesting fact

The transistor was invented at Bell Laboratories in December 1947 (first demonstrated on December 23) by John Bardeen, Walter Houser Brattain, and William Bradford Shockley, who were awarded the Nobel Prize in physics in 1956.

The field effect transistor (fet)

To control a bipolar transistor, you control the current flowing into or out of its base. The other type of transistor is the field effect transistor (FET). FETs work using control voltages instead. Accordingly they can be controlled with much smaller currents and are much more economic to use.

Interesting fact

No-one would build a computer with billions of bipolar transistors — the current in each transistor's base might be small, but when you add up all of the base currents in the millions of transistors, the computer as a whole would be consuming a great deal of electricity and making a great deal of heat. Not only is this wasteful, it would prevent manufacturers making a computer of convenient size. If the transistors were too close together, they would overheat.

A field effect transistor (FET). The diagram on the top shows the semiconductor structure. The diagram underneath shows its circuit symbol.

Questions & Answers

different structural formula
Lucas Reply
different type of structural formula
primary,secondary and tertiary
how does the earth revolute
Kevin Reply
What is the momentum
Given Reply
The product of the object's mass and it's velocity
electric field def
what is secondary alcohol?
is when Carbon that is bonded with OH is also bonded to 2 carbons of the chain.
how is ester formed
Aubrey Reply
how is n ester formed
Alcohol reacts with a carboxylic acid
and the reaction is catalysed by sulphuric acid
An ester is form when an alcohol reacts a carboxylic acid and sulphuric acid is used as a catalyst which therefore eliminates water.
an athlete with a mass of 70kg runs at a velocity of 45km . determine the athlete's momentum
Lesedi Reply
Is that a velocity or something else
45km/h i guess
Change to m/s
45km/h = 12.5 m/s p=mv =70×12.5 =875 kg.m/s
what are the measures of the rates of reaction
Lesego Reply
Volume Concentration Temperature Pressure Surface Area
the principle of superposition of waves
Sfundo Reply
what is work
Kool Reply
is this a group chat
Nobuhle Reply
Hey can y'all define newton's 2nd law
If a resultant force act on an object...the object will accelerate in the direction of a resultant force,the acceleration of the object is directly proportional to the net force and inversely proportional to the mass of the object
how do you calculate tension force
use the formula Fnet=ma if there is tension connecting two objects
to calculate Tension, usually calculate acceleration first Draw separate free body diagrams for each body. Apply Fnet = ma to calculate Tension
Hi people
when a resultant force acting on an object the object will accelerate in the direction of a force at an acceleration directly proportional to the force and invesly proportional to the mass of the object.
Hey people
how does temperature affect the equilibrium position
Blessing Reply
an increased temperature increases the average kinetic energy thus in turn increases the number of effective collisions........
so...which reaction is favored between endothermic and exothermic .when temperature is increased..?
exothermic reaction because energy is realised to the surroundings as heat and light energy ....graphical so much energy is realised as reactants to form product and because temperature is high rate of reaction is fast which means there is a successful collision
an object will continue in a state of rest unless it is acted upon an unbalanced force
Junior Reply
Newton's Law 1
First Newton's Law
Newton's first law
newton first law
Newton's first law
when pressure is increased what happen to volume
Siphelo Reply
care to explain?
if pressure is applied to a pistol , the volume will decrease and particles will collide more frequently with the wall of a container .Each time they collide with the wall they exert a force on them .More collision means more force and the pressure will increase , that Boyle's Law
Because the volume has decreased , the particle will collide more frequently with the wall of a container and each time they collide with the wall of a container they exert a force on them.More collision means more force so the pressure will increase , that Boyle's Law
what is the difference between momentum and a change in momentum?
Chavonne Reply
Change in momentum is the impulse of the object
Momentum is a vector quantity equal to the product of the mass of the particle and its velocity
How to name a branched molecule from right or left?
Vadin Reply
What's Free Fall
Senzo Reply
Free Fall means there is no acting force on that object.
only gravitational force
no external force acting on an object
by only force of gravite
but gravitational force
a motion in which the only force acting is gravitational force
and an object experiencing free fall is referred as a projectile

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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