ANGULAR VELOCITY

Angular Velocity is the rate of change of Angular Displacement.

Angular Velocity is a Vector Quantity

SI unit of Angular Velocity is Radians/sec

The Direction of Angular Velocity vector is perpendicular to the plane of rotation.

                                      Angular Displacement

Angular Velocity  =      -----------------------------------------

                                                 time

WHAT IS POWER FACTOR

Power Factor is a measure of how effectively the current is being converted into useful work output. A load with a power factor 1.0 represents most efficient loading of suply and a 
load with power factor 0.5 represents poor supply or much higher losses in the supply system.

or

Power Factor is the ratio between KW (Kilo-Watt) and the KVA (Kilo-volt-amp).  where KW is the actual load power and
KVA is the apparent load power.

DIFFERENCE BETWEEN KW AND KVA

Power Factor is the only difference between KW and KVA.

Power Factor is generally is an approximation. Unless it is

represented by the manufacturer.  The value of KVA
is generally larger than the KW.

ex:  consider power factor  is 0.95  

KW(kilo Watt) = Power Factor * KVA

                      = 0.95 * KVA 

or 

KVA( Kilo Volt Amp) = KW (Kilo Watt) / Power Factor

                               =  KW (Kilo Watt) / 0.95

USE OF ACTIVE VOICE AND PASSIVE VOICE

Though, In general Active voice is preferred, most
grammarians agree that the passive voice should be used when the receiver of the action is more important that the doer.

Eg: "The city was devastated by a tsunami"
                   (passive voice)
this sentence is better rather than

"A tsunami devastated the city"  (active voice)

so in this case passive voice is preferred to active voice.
 

TRANSCONDUCTANCE

The ratio of small change in plate current to the small change in grid voltage at constant plate voltage is known as transconductance or mutual conductance.

Transconductance or mutual conductance indicates the effectiveness of grid potential in changing the plate current.

AMPLIFICATION FACTOR OF VACUUM TUBE

The ratio of small change in plate voltage to a small change in grid voltage of a triode at constant plate current is known as amplification factor.

The amplification factor of a tube is a measure of its effectiveness of grid voltage relative to the plate voltage  in controlling the plate current.

VACUUM TUBE

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 (grids) for controlling the flow of electrons between cathode and anode.  These electrodes are housed in a highly evacuated glass envelope. The ability of vacuum tubes to conduct current in vaccum enables them to perform different functions.

SECONDARY EMISSION

Electron emission from a metallic surface by the bombardment of high speed electrons or other particles is known as secondary emission.

In this method, a high velocity beam of electrons strikes the metal surface and causes the free electrons of the metal to be knocked out from the surface.

FIELD EMISSION

The process of electron emission by the application of strong electric field at the surface of a metal is known as field emission

In this method, a strong electric field is applied at the metal surface which pulls the free electrons out of metal because of attraction of positive field.  The stronger the electric field, the greater is the electron emission.

PHOTO ELECTRIC EMISSION

Electron emission from a metallic surface by the application of light is known as photo electric emission

In this method, the energy of light falling upon the metal surface is transferred to the free electrons within the metal to enable them to leave the surface.  The greater the intensity of light beam falling on the metal surface, the greater is the photo electric emission.

THERMIONIC EMISSION

The process of electron emission from a metal surface by supplying thermal energy to it is known as thermionic emission.

In this method, the metal is heated to sufficient temperature (about 2500 deg c) to enable the free electrons to leave the metal surface.  The number of electrons emitted depends upon the temperature.  The higher the temperature, the greater is the emission of electrons. this type of emission is employed in vacuum tubes.

TYPES OF ELECTRON EMISSION

The electron emission from the surface of a metal is possible only if sufficient additional energy is supplied from some external source. This external energy may come from a variety of sources such as heat energy, energy stored in electric field, light energy etc.,

there are four principal methods of obtaining electron emission from the surface of a metal

1) Thermionic emission: 
In this method the metal is heated to sufficient temperature (about 2500 deg C) to enable the free electrons to the leave the metal surface.  The number of electrons emitted depends upon the temperature.  The higher the temperature, the greater is the emission of electrons.  This type of emission is employed in vacuum tubes.

2)Field emission:
In this method, a strong electric field (high positive voltage) is applied at the metal surface which pulls the free electrons out of metal because of the attraction of positive field.  The stronger the electric field, the greater is the electron emission.

3)Photo-electric emission:
In this method, the energy of light falling upon the metal surface is transferred to the free electrons within the metal to enable them to leave the surface.
The greater the intensity of light beam falling on the metal surface, the greater is the photo electric emission.

4)Secondary emission:
In this method, a high velocity beam of electrons strikes the metal surface and causes the free electrons of the metal to be knocked out from the surface.

WORK FUNCTION OF A METAL

The amount of additional energy required to emit an electron from a metallic surface is known as Work function of that metal

ELECTRON EMISSION

The liberation of electrons from the surface of a substance is known as electron emission.

NORTON'S THEOREM

Any network having two terminals A and B can be replaced by a current source of output Ia in parallel with a resistance Ra.

i) The output Ia of the current source is equal to the current that would flow through AB when A and B are short circuited.

ii) The resistance Ra is the resistance of the network measured between terminals A and B with load (Rc) removed and sources of e.m.f replaced by their internal resistances, if any

Norton's theorem is converse of thevenin's theorem.

SEMI CONDUCTOR

A Semi Conductor is a substance which has very few free electrons at room temperature. under the influence of potential difference, a semi conductor practically conducts no current.

INSULATOR

An insulator is a substance which has practically no free electrons at ordinary temperature.  Therefore, an insulator does not conduct current under the influence of potential difference.

CONDUCTOR

Conductor is a substance which has a large number of free electrons.  When the potential difference is applied across a conductor, the free electrons move towards the positive terminal of supply, constituting electric current.

ELECTRON

An electron is a negatively charged particle having negligible mass. mass of an electron is very small as compared to its charge. it is very mobile and is greatly influenced by electric or magnetic fields.

ATOMIC WEIGHT

The sum of protons and neutrons constitutes the entire weight of an atom and is called atomic weight