What is Electronics ?
Electronics is the science of how to control electric energy.
Electronic components can be divided into two groups: Active elements and Passive elements.
Anyone with an interest to learn basic electronics will want to begin learning how to read a schematic and build a circuit using standard electronic components.
Circuits are commonly built using discrete (meaning separate) electronic components which can be selected individually and put together to make a circuit.
Examples of discrete components include resistors, capacitors, diodes and transistors.
Discrete components can also be used as components in circuits that include an integrated circuit
Typical Active Components
In order for a circuit to be properly called electronic it must contain at least one active device.
All active devices control the flow of electrons through them. Some active devices allow a voltage to control this current
while other active devices allow another current to do the job
- Batteries
- Generators
- Valves (Vacuum Tubes)
- Transistors
- Silicon-controlled rectifiers (SCRs - aka Thyristors)
- TRIACs.
- Photovoltaic Cell
Typical Passive Components
Components incapable of controlling current by means of another electrical signal are called passive devices.
- Resistors
- Capacitors
- Inductors
- Transformers
Depending on useage even diodes could be considered passive devices
Electrical Charge
Electrical charge relates to voltage, current, and resistance.
The three basic principles can be explained using electrons, or more specifically, the charge they create:
- Voltage is the difference in charge between two points.
- Current is the rate at which charge flows.
- Resistance is a material’s tendency to resist the flow of charge (current).
These values, describe the movement of charge and a circuit is the path of charge moving from one place to another.
Components in a circuit control this charge and use charge to do work.
The rarely used unit of electric charge is a Coulomb (C)
which is the quantity of charge that passes through an electrical conductor carrying one ampere within one second.
Ohms Law
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.
The fundamental relationship between voltage, current and resistance in an electrical circuit is called Ohm’s Law. Ohm’s Law is a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity and electronics that it needs to be committed to memory by the serious student.
For those not comfortable with algebra, there’s a trick to remembering how to solve for any one quantity, given the other two.
First, arrange the letters V, I, and R in a triangle like this:
This gives us three equations
Resistance (Ω) =
Voltage(V)
/
Current(I)
in Ohms(Ω)
Current (I) =
Voltage(V)
/
Resistance(Ω)
in Amperes(A)
Voltage (V) =
Current(I)
x
Resistance(Ω)
in Volts(V)
Electrical Voltage
Voltage, ( V ) is the potential energy of an electrical supply stored in the form of an electrical charge.
Voltage can be thought of as the force that pushes electrons through a conductor and the greater the voltage
the greater is its ability to “push” the electrons through a given circuit.
The difference in voltage between any two points(called junctions or nodes) in a circuit is known as the Potential Difference, ( p.d. )
commonly called the Voltage Drop.
Electrical Resistance
Electrical resistance R in Ohms (Ω) of a conductor is a measure of how difficult it is to push the charges along.
Using the flow analogy, electrical resistance is similar to friction. For water flowing through a pipe, a long narrow pipe provides more resistance
to the flow than does a short fat pipe. The same applies for flowing currents: long thin wires provide more resistance than do short thick wires.
A material with a very large value of Resistance will pass almost no current (electrical insulator),
while another material with very small Resistance will yield a large current for the same voltage (good electrical conductor).
Electrical Current
Current, (A) is a flow of electrical charge. Usually the symbol used for current is the uppercase letter I
(which originates from the French phrase intensité de courant, meaning current intensity).
The standard unit for the ampere is more usually shortened to Amp.
A circuit with higher resistance has less current flowing through it. Current is a rate quantity and in Electrical engineering power sources
are usaully expressed in the terms Ampere Hours or A/H.
Convention takes the direction of electric current as if it were the positive charges which are moving. Some texts reverse this convention and
take electric current direction as the directional flow of the electrons (the charge carriers), an obviously more physically realistic direction,
the conventional current direction is the flow of positive charge from high voltage to low voltage
Passive Elements
Resistors
Resistors are electrical components that oppose the flow of current. As passive components, resistors can
only reduce voltage or current signals and cannot increase them. The resistance of an element is its measure of opposition
to electrical charge flow
Between three and five bands are placed on the resistor for indication, Bands read from left to right (end to center).
The first band will be close to the end and will not be isolated; the last band is generally spaced farther apart from the rest.
Four bands are placed on most resistors. When four bands are present:
- The first band represents the first digit of resistance.
- The second band represents the second digit of resistance.
- The third band indicates the multiplier.
- The fourth band indicates the tolerance.
Resistor Colour Code
Many years ago whilst I was at college, I was taught lots of mneumonics. With most having been long been forgotten,
I guess the resistor colour code mneumonic has stuck mainly as its vulgar and has been a great time saver so extremely useful to remember.
"Bad boys rape our young girls but virgins go without"
- B Black
- B Brown
- R Red
- O Orange
- Y Yellow
- G Green
- B Blue
- V Violet
- G Grey
- W White
With 4 banded resistors the 3rd band colour is omitted therefore the resistor has two bands for the numerical value followed by the multiplier with the tolerance band separated from these. the tolerenaces are usually 10%, 5% or 2%
