THIRD TERM LESSON NOTE FOR WEEK THREE.
SUBJECT : BASIC TECHNOLOGY
TOPIC : BASIC ELECTRONICS EMISSION.
DURATION : 40 MINUTES
PERIOD : SINGLE PERIOD (Twice in a week)
REFERENCE BOOK :
- BASIC TECHNOLOGY FOR JUNIOR SECONDARY SCHOOL, JSS 3.
- SCHEME OF WORK FOR JUNIOR SECONDARY SCHOOL JSS 1 – 3.
- ONLINE RESOURCES
CONTENT :
Basic Electronics Emission.
The emission is the displacement or dislodgement of electron from a material to a pre-determined position or object. The basic electron emission occurs when heat, sunlight, electron collision, electro-magnetic fieldand surface bombardment are used to release electrons from the metal surface to the vacuum tube.
Therefore, Electron emission can be define as the process or method of liberating or emitting free electrons from the metal surface to the vacuum tubes.
A vacuum tube is an empty tube in which all the air had been completely removed and used for the purpose of storing liquefied gas.
Methods of Emission.
Free electrons are the electrons that are released from the surface of metal. Four principal methods of emitting or liberating electrons from the surface of a metal are:
1. The thermionic emission: This is also called the primary 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.
2. The Photo electric emission: the photo electric emission 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 and automatic door openers.
The cold-cathode emission: is also called field emission. The cold-cathode emission is the method is the method by which free electrons are emitted from the surface of metal by the application of magnetic field or electric fields. It is used in operation of electron microscopes.
3. The Secondary Emission: The secondary emission is the method by which free electrons are emitted from the surface of a metal by the application of kinetic energy.
COMPONENTS AND USES OF ELECTRONIC DEVICE.
INTEGRATED CIRCUIT (I.C)
The integrated circuit (I.C) is an electronic component that contains the following electronic devices in one single unit to reduce the size of electronic appliances. These electronic devices functions as a result of electron movement in the circuit. They include;
i. The diodes
ii. The semi conductors
iii. The transistors
iv. The gas discharge tube
v. The capacitors
vi. The resistors
vii. The inductors.
All these electronic devices are found in electronic appliances and equipment, Such as in radios, computers, televisions, and so forth. These electronic devices are electrically assembled, connected and soldered together on one circuit board, so that the electric current can flow in them. When all these electronic devices are electrically connected together in one unit of a circuit board, they integrated into one; hence the name is called an INTEGRATED CIRCUIT (I.C).
1) THE DIODES: The diode is an electronic device that has two terminals called electrodes. One of the electrodes is positive (+ve) while the other is negative (-ve). The diode is an electronic device which depends on the principle that electrons flow from the cathode (emitter) to the Anode (collector). This means that, while the diode is connected to a circuit, electrons flow in one direction only (from cathode to anode).
The diode has two operating system modes.
Forward bias
Backward bias.
The diode contains two metals called electrodes placed directly opposite each other inside a vacuum tube. These electrodes are:
i. The cathode
ii. The anode.
The cathode has a negative charge and is an electron emitter. Therefore, the cathode is an electron donor.
The anode has a positive charge and is an electron collector and is also an electron acceptor.
Uses: The diodes are used as
Rectifier in order to convert a.c. supply to d.c. supply.
The diodes make the current to flow in one direction only. Therefore, the current in the diode is uni-directional.
2) THE TRIODES: the triode is an electronic device which has three electrodes, namely:
i. The cathode (emitter)
ii. The anode (collector)
iii. The grid.
A voltage is required for the heater to heat the cathode to enable it to emit electrons.
A voltage is required for the grid to control the movement of the electrons from the cathode (Emitter) to the Anode (collector).
A voltage is required by the anode to attract the electrons.
The main function of grid in the triode is to control the movement of the electrons from the cathode plate to the Anode plate.
Uses of Triode: The triode is primarily used as
Amplifier when connected to the cathode plate (emitter) to control the generation of electric current for Radios, Televisions etc.
3) OSCILLATORS: These are part of the current flowing between the emitter and collector and are directed to the grid, which controls the movements of electrons in the triode. The oscillators are used to generate radio frequencies used in all forms of radio frequencies used in all forms of radio communication system.
4) THE SEMI CONDUCTORS: The semi conductors materials are those substances whose electrically conductivity lies between that of good conductors (metallic substances) and good insulators (non-metallic substances). The two common semi conductor materials are: Silicon and Germanium.
5) TRANSISTORS: Transistors are the most important active device in electronic today. A transistor is a semi conductor material that made up of three electrode terminals: The Emitter (E), The Base (B) and The Collector (C).
6) 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 current in an electric circuit).
7) INDUCTORS: inductors are devices used to store energy in the form of a magnetic field. An inductor is made up of coils of wires and sometimes wound on a core. Iron is the commonest example of a core material use in inductors.
8) INDUCTANCE: An inductance is the ability of an inductor to store energy in its magnetic field. When inductors carry current, they behave like magnets.
ELECTRICAL AND ELECTRONIC SYSMBOLS.
ASSIGNMENT
1. Mention the four method of basic electronic emission.