TCOM 308

Basics of Electronics

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

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

Electrons

Electrons

Whirling in orbit around nucleus

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

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.

Conductors

Representation of number of free electrons in three substances

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

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

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

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

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

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

Circuit

Circuit

+_

Incandescent lamp

Battery

Schematic symbols used in electronics

Circuit

• Circuit is composed of – a source or multiple sources of emf– a lode or the wire, devices, etc. through which the

current flows

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

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

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)

Resistance

• Factors affecting resistance:– Length of conductor– Cross-sectional area of conductor– Temperature of conductor– Composition of conductor or material

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

Ohm’s law

• Resistance X Current = Voltage (E=R X I)• Voltage ÷ Current = Resistance (R=E ÷ I)• Voltage ÷ Resistance = Current (I=E ÷ R)

Ohm’s law

EI R