1. TCOM 308
Basics of Electronics

2. Electronics Electronics is the study of Electrons
The word “electricity” is derived from the Greek word “elektron” which means “amber”
Probably because rubbing amber on cloth created a static electrical charge

3. Electrons One of three types of subatomic particles
Protons (+) are positively charged particles in the nucleus of an atom
Neutrons (0) are non-charged or neutral particles in the nucleus of an atom
Electrons (-) are negatively charged particles in orbit around the nucleus of an atom
Electrons are held in orbit by the oppositely charged protons

4. Electrons

5. Whirling in orbit around nucleus
Electrons
Whirling in orbit around nucleus

6. Conductors
Some substances contain an excess of electrons compared to the number of protons
Excess electrons are known as “free electrons”
Substances with an abundance of free electrons are known as conductors
Conductors allow free electrons to easily be dislodged

7. Conductors
The best conductors are metals, which naturally contain excess free electrons
The best conductor is silver – but expensive
Gold is an excellent conductor – but also expensive
Other good conductors include copper, aluminum, steel, brass, bronze, etc.

8. Representation of number of free electrons in three substances
Conductors
Representation of number of free electrons in three substances

9. Insulators
Substances with a shortage of electrons are called insulators
Electrons are difficult to dislodge from their orbits and resist flowing
Non-conductors include glass, rubber, fiberglass, porcelain, ceramic, plastic, air, diamond

10. Current flow
Electron flow through a conductor is called (electrical) current
Particles with the same electrical charge repel one another
Particles with opposite electrical charges attract one another
Since electrons are negative, current flows from the negative to the positive

11. Current flow
Electrons move from one atom to the next, where more electrons are dislodged, and those electrons flow to the next atom, and so on

12. Current flow
To start current flowing, some “force” or “pressure” is require to push the electrons out of their orbits
This force is called electro-motive force or emf
EMF is referred to as a “potential”
EMF may thought of as a negative charge that will push the first electrons out of orbit and start current flowing through a circuit
EMF is measured in volts

13. Current flow
The “volume” or quantity of electrons moving is referred to as the amount of current flow
The amount of current flow is the amount of electricity flowing
Current flow is measured in amperes or amps

14. Current flow For current to flow then we need:
A source of emf
A conductor
A circuit
Circuit is a closed path or “circle”
The circuit ends where it began

15. Circuit

16. Schematic symbols used in electronics
Circuit
Schematic symbols used in electronics
Incandescent lamp _ +
Battery

17. Circuit Circuit is composed of a source or multiple sources of emf
a lode or the wire, devices, etc. through which the current flows

18. Direct current Batteries supply emf to move electrons in one direction
When electron movement is one direction only, the current is known as direct current or DC
Electrons are always moving toward the positive post of the battery

19. Alternating current
Generators can supply emf to move electrons in two directions – vibrating back & forth
When electrons move in two directions, the current is known as alternating current or AC
Electrons move back and forth between atoms

20. Resistance
Because electrons do have mass, and because they are held in orbit by their electrical charges, they are reluctant to leave orbit
This reluctance is called resistance
Resistance is measured in ohms (Ω)

21. Resistance Factors affecting resistance: Length of conductor
Cross-sectional area of conductor
Temperature of conductor
Composition of conductor or material

22. Ohm’s law Three variables in the circuit:
EMF is measured in volts and expressed by the symbol E
Current flow is measured in amperes and expressed by the symbol I
Resistance to current flow is measure in ohms and expressed by the symbol R
If we know any two variables we can calculate the third using a formula known as Ohm’s law

23. Ohm’s law Resistance X Current = Voltage (E=R X I)
Voltage ÷ Current = Resistance (R=E ÷ I)
Voltage ÷ Resistance = Current (I=E ÷ R)

24. Ohm’s law E I R