CONTENTS
1.0 Basic Emission Theory
2.0 Basic Electronic Devices
1.0 Basic Emission Theory
1.1 What is emission?
Emission is the displacement or dislodgement of electron from a material with the intention of directing such electron to a predetermined position or object. The basic electronic emission occurs when heat, sunlight, electron collision, electromagnetic field and surface bombardment are used to release electron from the metal surface to the vacuum tube.
1.2 Electronic Emission
The electronic emission is the process of liberating or emitting free electrons from the metal surface to the vacuum tubes. A vacuum tube is an empty tube in which the air has been completely removed for the purpose of storing liquefied gas.
1.3 Methods of Emission
There are four principal methods of liberating electron from the surface of metal:
-The thermionic emission
-The photo-electric emission
-The cold-cathode emission
-The Secondary emission
The Thermionic Emission: The thermionic Emission is the method by which free electrons are emitted from the surface of a metal by the application of heat energy. Another name for thermionic emission is THE PRIMARY EMISSION.
The Photo-Electric Emission: This is the method by which free electrons are emitted from the surface of a metal by the application of light or rays of light. It is used in solar panel.
The Cold Cathode Emission or Field Emission: This is the method by which free electrons are emitted from the surface of metal by the application of magnetic fields or electric field. It is used in the operation of electron microscope.
The Secondary Emission: This is the method by which electrons are emitted from the surface of a metal by the application of kinetic energy. A stream of moving electrons is called electron.
2.0 BASIC ELECTRONIC DEVICES
The basic Electronic devices are the devices which emit and control the movement of electrons in a desirable manner used in generation of electronic appliances.
2.1 Types of Basic Electronic Devices
Semi-conductor
Resistor
Capacitors
Transistors etc
Semi Conductors: Semi-conductors are those substances whose electrically conductivity lies between the good conductors (metallic substances) and good insulators (non-metallic substances) E.g. Silicon, Germanium.
2.2 Types of Semi Conductors
-The intrinsic semi-conductor also known as pure semi-conductor
-The extrinsic semi-conductor also known as impure semi-conductors.
Resistor: A Resistor is a device used to control the flow of electric current in an electric circuit or which opposes the flow of electric circuit. The ability of a Resistor to control the flow of electric current is called RESISTANCE. The resistor is measured in Ohms by a device called Ohm meter.
Capacitor: A capacitor is a piece of a[apparatus designed to store electrical energies in the form of electric charges. An example of capacitor is Condenser or starter in a fluorescent lamp. The capacitors are available in motor vehicles and air conditioner etc.
Capacitance: this is a phenomenon which exists when certain parts of an electric circuit are able to store electric charges. Capacitance (C) = Charge on either plate (Q)/P.d across the plates (V). The S.I unit of a capacitance is farad (F)
Transistors: Transistors are semi-conductor materials which are capable of providing amplification in electronic equipment. They are smaller than vacuum tubes; the vacuum tubes control the flow of electron in the airless space while the transistors control the flow of electrons in the semi-conductors materials.Transistor has three electrodes in terminals:
The Emitter(E)
The Base(B)
The Collector(C)
The types of transistors are:
-The bipolar transistor. E.g. (a) The P-N-P Transistor which are mostly made of
-Germanium (b) The N-P-N Transistors which are mostly made of silicon
-The field effect transistor
2.3 Uses of Basic Electronic Devices
- Transistor is used to amplify current. An Amplifier is a circuit that increases the input signal
-Transistor is used as a sensitive switch
-Resistor is used to control the current that flows in the bulb
-Capacitors are used for air conditioning
