EMITTER, COLLECTOR AND BASE OF A TRANSISTOR

A transistor has three sections, The section on one side is Emitter, and the section on the opposite side is the collector.  The middle section is called the base.

Emitter:
The section on one side that supplies charge carriers (electrons) is called the emitter. The emitter is always forward biased with respect to base.

Collector:
The section on the other side that collects the charges is called the collector. the collector is always reverse biased.  Its function is to remove charges from its junction with base.

Base:
The middle section which forms two pn junctions between the emitter and collector is called the base.
The base emitter junction is forward biased and the base-collector junction is reverse biased.

TRASISTOR

When a third doped element is added to a crystal diode in such a way that two pin junctions are formed, the resulting device is known as transistor.

A transistor consists of two pn junctions formed by
sandwiching either p type or n type semiconductor between a pair of opposite types.

there are two types of transistors

1) n-p-n transistor
2) p-n-p transistor


A n-p-n transistor is composed of two n-type semiconductors separated by a thin section of p-type semiconductor. 

A p-n-p transistor is composed of  two p-type semiconductors separated by a thin section of n-type semi conductor.

In any transistor, there are two pn junctions.  therefore a transistor may be regarded as a combination of two diodes connected back to back.

There are three terminals in a transistor  1) Emitter
2)Collector    3) Base

WHAT IS A COLUMN, SHORT COLUMN, LONG COLUMN

Column:
A column is a vertical compression member.  A column is subjected to axial compressive loads.

Short Column:
When the ratio of effective length to the least lateral dimensions of the column is less than 12, then it is
called a short column.

(or)
When the ratio of effective length to the least radius of gyration is less than 45, then it is called a short column

Long Column:
When the ratio of effective length to the least radius of gyration is greater than 45, then it is called a long column.

A long column is subjected to bending moment in addition to direct compressive stress.

The load carrying capacity of a long column is less than a short column

The load carrying capacity of a long column depends upon slenderness ratio (slenderness ratio increases then the capacity of the column decreases)

WHAT IS FOREX, FOREIGN EXCHANGE MARKET

Foreign Exchange, simply called Forex
also called as currency market.  Simultaneous purchase and sale of one country's currency to
another country's currency.  in simple terms
buying of one currency and selling another currency at the same time.

The world currencies do not have a fixed exchange rates and they are always fluctuating.

Forex trading allows an investor to participate in profitable fluctuations of world currencies.

FREEZING OF LAYERS IN AUTOCAD

Freezing of a layer means it freezes the selected layer in all viewports, including the Model Tab.  You can freeze layer to speed up zoom, Pan and many other operations and to improve object selection performance, reduce regeneration time for complex drawings. 

Use Freeze option, if you want a layer to be invisible for long periods.  If you plan to switch visibility settings frequently, use the on/off setting to avoid regenerating the drawing. 

CUP AND CONE FRACTURE

Mild Steel specimen features with cup and cone fracture.  Cup and Cone fracture is the characteristic property of mild steel.

BENDING STRESS

Bending stresses are produced in beams due to bending moment.  The bending moment is also called as flexural stress or skin stress.  it is denoted by the letter "f".

                  M
         f  =  ____

                  Z

where  M= Bending moment
           Z=  Section Modulus ( I/Y)

SHEAR STRESS OR TANGENTIAL STRESS

when the Force acts tangential to the area of cross section it is called shear stress or tangential stress.  The stress produce by shear force is called shear stress or tangential stress.  shear stress is the ratio of shear force to shear area.

ZENER DIODE

A properly doped crystal diode which has a sharp breakdown voltage is known as zener diode.  A zener diode is like an ordinary diode except it is properly doped.   A zener diode is always reverse connected (reverse biased)  Zener diode has sharp breakdown voltage i.e zener voltage.

ZENER CURRENT, ZENER VOLTAGE

When the reverse bias on a crystal diode is increased, a critical voltage, called break down voltage is reached.  where the reverse current increases sharply to a high value.  The explanation for the breakdown region is given by C.Zener.  therefore breakdown voltage is called zener voltage and the sudden increase in current is known as zener current.
The breakdown or zener voltage depends upon the amount of doping.  If the diode is heavily doped, depletion layer will be thin and consequently the breakdown of the junction will occur at a lower reverse voltage.  A lightly doped diode has a higher break down voltage.

FILTER CIRCUITS

A Rectifier is required to produce pure D.C supply for using at various places in the electronic circuits.  However, the output of a rectifier has pulsating character.  It contains A.C and D.C components.  The A.C component is undesirable  and must kept away from the load.  To do so, a filter circuit is used which removes the A.C component and allows only the D.C component to reach the load.

A filter circuit is a device which removes the A.C component of rectification output but allows the D.C component to reach the load.

RIPPLE FACTOR

The output of a rectifier consists of a D.C component and an A.C component ( also known as Ripple)
The A.C component is undesirable and accounts for the pulsation in the rectifier output.  The effectiveness of a rectifier depends upon the magnitude of A.C component in the output.  The smaller this component, the more effective is the rectifier.

The ratio of r.m.s value of A.C component to the D.C component in the rectifier output is known as Ripple Factor.   Ripple factor is very important in deciding the effectiveness of a rectifier.

FULL WAVE RECTIFIER

In full wave rectification, current flows through the load in the same direction for both half-cycles of input A.C voltage.  This can be achieved with two diodes working alternatively.  For the positive half cycle of input voltage one diode supplies current to the load and for the negative half cycle the other diode does so, current being always in the same direction through load.  Therefore a full wave rectifier utilises both half cycles of input A.C voltage to produce the D.C output.

EFFICIENCY OF HALF WAVE RECTIFIER

The ratio of D.C power output to the applied input A.C power is known as Rectifier Efficiency.

HALF-WAVE RECTIFICATION

In Half-wave rectification, the Rectifier conducts current only during the positive half cycles of input A.C.Supply.  The negative half-cycles of A.C supply are suppressed.  i.e during negative half cycles no current is conducted and hence no voltage appears across the load.  Therefore current always flow in one direction (i.e D.C) through the load.

SEMI CONDUCTOR DIODE

A p-n junction is known as semi conductor diode or crystal diode.  The out standing property of a crystal diode to conduct current in one direction only permits it to be used as a rectifier.

P-N JUNCTION

p-n Junction conducts current easily when forward biased and practically no current flows when it is reverse biased.  This unilateral conduction characteristic of P-n junction is similar to that of a vacuum diode.

DISADVANTAGES OF HALF-WAVE RECTIFIER

Half-wave rectifier is seldom used in practice because
1) The rectification efficiency is low
2) The D.C output is small
3) Secondary transformer carries the rectified current, thus producing direct magnetisation of the transformer core.
4) Because of short heavy pulses of current, the heating of transformer winding is large compared to the current delivered.

RECTIFIER

Rectifier is an electronic device that converts alternating current into direct current is called rectifier.
A rectifier changes A.C into D.C by eliminating the negative half cycles of the alternating voltage.  It may work as a switch that closes a load circuit during the positive half cycle of A.C supply and opens the circuit during the negative half cycle.  Therefore a rectifier provides one-way path for electric current.

VACUUM TUBE

Vaccum Tube is an electronic device in which the flow of electrons is through a vacuum is known as vacuum tube.  A vacuum tube usually contains a cathode which is the electron emitter, an anode(plate) which is the electron collector and one or more electrodes (called grids) for controlling the flow of electrons between cathode and plate.  These electrodes are housed in a highly evacuated glass envelope.  The plate is held at positive terminal with respect to cathode so that emitted electrons are attracted to plate to provide current in vaccum.