The resistance value is specified in ohms, the standard symbol is
"R" or Ω. Resistor values are often stated as "k" (kilo, or times
1,000) or "M", (meg, or times 1,000,000) for convenience. There are
a few conventions that are followed, and these can cause problems
for the beginner. To explain - a resistor has a value of 2,200
Ohms. This may be shown as any of these:
The use of the symbol for Ohms (Omega, Ω is optional, and is most
commonly left off, since it is irksome to add from most keyboards.
The letter "R" and the "2k2" conventions are European, and not
commonly seen in the US and other backward countries :-) Other
variants are 0R1, for example, which means 0.1 Ohm
The schematic symbols for resistors are either of those shown
below. I use the Euro version of the symbol exclusively.
Fig - 2 :Resistor Symbols
The basic formula for resistance is Ohm's law, which
1. R = V / I Where V is voltage, I is current, and R is
The other formula you need with resistance is Power (P)
2. P = V2 / R
3. P = I2 * R
The easiest way to transpose any formula is what I call the
"Transposition Triangle" - which can (and will) be applied to other
formulae. The resistance and power forms are shown below - just
cover the value you want, and the correct formula is shown. In case
anyone ever wondered why they had to do algebra at school, now you
know - it is primarily for the manipulation of a formula - they just
don't teach the simple ways. A blank between two values means they
are multiplied, and the line means divide.
Fig - 3 :
Triangles for Resistance
- 4 : Resistor
The tolerance of resistors is mostly 1%, 2%, 5% and 10%. In the
old days, 20% was also common, but these are now rare. Even 10%
resistors are hard to get except in extremely high or low values (>
1M or < 1R), where they may be the only options available at a
A 100R resistor with 5% tolerance may be anywhere between 95 and 105
ohms - in most circuits this is insignificant, but there will be
occasions where very close tolerance is needed (e.g. 0.1% or
better). This is fairly rare for audio, but there are a few
instances where you may see such close tolerance components.
Resistors are available with power ratings of 1/8th W (or less for
surface mount devices), up to hundreds of watts. The most common
are 1/4W (0.25W), 1/2W (0.5W), 1W, 5W and 10W. Very few projects
require higher powers, and it is often much cheaper to use multiple
10W resistors than a single (say) 50W unit. They will also be very
much easier to obtain.
Like all components, it is preferable to keep temperatures as low as
possible, so no resistor should be operated at its full power rating
for any extended time. I recommend a maximum of 0.5 of the power
rating wherever possible. Wirewound resistors can tolerate severe
overloads for a short period, but I prefer to keep the absolute
maximum to somewhat less than 250% - even for very brief periods,
since they may become open circuit from the stress, rather than
temperature (this does happen, and I have experienced it during
tests and repairs).
: Resistors are made from a number of different materials. I shall
only concentrate on the most common varieties, and the attributes I
have described for each are typical - there will be variations from
different makers, and specialized types that don't follow these
(very) basic characteristics. All resistors are comparatively
Low to medium power. Comparatively poor tolerance and stability.
Noisier than most others.
Carbon Film: Low power. Reasonable tolerance and
stability. Reasonably quiet.
Metal Film: Low to medium power. Very good tolerance and
Wirewound: High to very high power. Acceptable to very
good tolerance, good stability. Quiet. May have inductance.
Resistors make noise. Everything that is above 0K (zero Kelvin,
absolute zero, or -273 degrees Celsius) makes noise, and resistors
are no exception. Noise is proportional to temperature and
voltage. Low noise circuits will always use low resistor values and
low voltage wherever possible.
Resistors may also have inductance, and Wirewound types are the
worst for this. There are non-inductive Wirewound resistors,
but are not readily available, and usually not cheap.
Two Resistors in Parallel
Learn More on Basics of Electronics:
the branch of
science that deals with the study of flow and control of
electrons (electricity) and the study of their behavior and
effects in vacuums, gases, and semiconductors, and with devices
using such electrons.
Rules of Electrical
* A voltage of 1V across a resistance
of 1 Ohm will cause a current flow of 1 Amp, and the resistor will
dissipate 1 Watt (all as heat).
is an electronic circuit?
A circuit is a structure that directs
and controls electric currents, presumably to perform some useful
function. The very name "circuit" implies that the structure is
closed, something like a loop.
Charge is mobile and can flow freely in certain
materials, called conductors. Metals and a few other elements and
compounds are conductors. Materials that charge cannot flow through
are called insulators. Air, glass, most plastics, and rubber are
insulators, for example. And then there are some materials called
semiconductors, that seemed to be good conductors sometimes but much
less so other times. Silicon and germanium are two such materials.
The flow of charge is called electrical current. Current is measured
in amperes (a), amps for short (named after another French scientist
who worked mostly with magnetic effects).
There are many different representations for basic
wiring symbols, and these are the most common. The conventions
I use for wires crossing and joining are marked with a star (*) -
the others are a small sample of those in common use, but are fairly
representative. Many can be worked out from their position in
the circuit diagram (schematic).
Voltage is something is a type of "pressure" that drives electrical
charges through a circuit.
charges attract, they exert a force on each other pulling them
together. The magnitude of the force is proportional to the product
of the charge on each mass.
What is charge?
may be defined as the quantity of unbalanced electricity in a body
(either positive or negative) and construed as an excess or
deficiency of electrons.
Charge comes in two forms,
positive (+) , and negative charge ( - ) .
Charges can be separated by several means to produce
a voltage. A battery uses a chemical reaction to produce energy and
separate opposite sign charges onto its two terminals. As the charge is
drawn off by an external circuit, doing work and finally returning to
the opposite terminal, more chemicals in the battery react to restore
the charge difference and the voltage. The particular type of chemical
reaction used determines the voltage of the battery, but for most
commercial batteries the voltage is about 1.5 V per chemical section or
Ohm's law describes the relationship between
voltage, V , which is trying to force charge to flow, resistance, R
, which is resisting that flow, and the actual resulting current I .
the Electric energy produced per unit time.
In simple words, we can say that a capacitor is a device
used to store and release electricity, usually as the result
of a chemical action. Also referred to as a storage cell, a
secondary cell, a condenser or an accumulator. A Leyden Jar
was an early example of a capacitor.
An inductor is
an electrical device (typically a
conducting coil) that introduces inductance into a circuit.
An inductor is a passive electrical component designed to
provide inductance in a circuit. It is basically a coil of
wire wrapped around an iron core. simplest form an inductor
is made up of a coil of wire. The inductance measured in
henrys, is proportional to the number of turns of wire, the
wire loop diameter and the material or core the wire is
A conductor made with semiconducting
material. Semiconductors are made up of a substance with electrical
properties intermediate between a good conductor and a good
insulator. A semiconductor device conducts electricity poorly at
room temperature, but has increasing conductivity at higher
temperatures. Metalloids are usually good semiconductors.
Silicon, atomic number 14 on the periodic table, is a semiconducting
material from which integrated circuits (computer chips of all
types--processors, memory chips, etc.; CCDs; transistors; etc.) are
Silicon is one of the most common elements. Silicon is also the
semiconductor material out of which almost all modern transistors are
A Diode is
an electronic device that allows
current to flow in one direction only. It is a semiconductor that consists of a p-n junction. They are used
most commonly to convert AC to DC, because they pass the
positive part of the wave, and block the negative part of
the AC signal, or, if they are reversed, they pass only the
negative part and not the positive part.
Electronic Component name abbreviations:
Here is a list of Electronic Component name abbreviations
widely used in the electronics industry.
What is Energy Star?
Home Electrical Wiring Types and Rules
Surface Mount Device (SMD) or Surface Mount Electronic Components
SMD Resistor – Surface Mount Chip Resistor Guide
All about Semiconductor
Ball Grid Array (BGA) Package
SMD Surface Mount Electronic Components for SMT
How to Solder – Hand Soldering Tutorial
Printed Circuit Board: Design, Diagram and Assembly
Active and Passive Electronic Components
Electronic Components, Parts and Their Function
How Electronic / Electrical Circuit Works
How to Generate Electricity – How is Electricity Generated