Introduction to Electronics
These are my notes on an introduction to electronics.
Table of Contents
What is Electronics
Introduction
Electrical systems use electric current to power things such as light bulbs.
Electronic systems go a step further. They control the current, switch it on and
off, change its fluctuations, direction, and timing in various ways to
accomplish a variety of functions.
The word electronics describes both the field of study that focuses on the control of
electrical energy and the physical systems that implement this control of
electrical energy. To understand what it means to control electric current, you
need a good working sense of what electric current is.
The term electricity can lead to confusion, even among scientists. Generally
speaking, electricity has to do with how certain types of particles in nature
interact with each other when in close proximity.
Electric charge is a fundamental property of certain particles that describes
how they interact with each other. There are two types of electric charges:
positive and negative. Particles of the same type repel each other, and
particles of the opposite type attract each other.
Electrical energy is a form of energy caused by the behavior of electrically
charged particles.
Electric current is the movement or flow of electrically charged particles. This
connotation of electricity is probably the one you are most used to.
Electric Current
Electric current is the movement in the same direction of small, electrically
charged particles called electrons.
Atoms are the basic building blocks of everything. Every atom contains the
following types of subatomic particles:
1. Protons carry a positive electric charge and exist inside the nucleus or
center.
2. Neutrons have no electric charge and exist along with protons inside the
nucleus. and exist inside the nucleus or center.
3. Electrons carry a negative charge and are located outside the nucleus in an
electron cloud.
The specific combination of protons, electrons, and neutrons in an atom defines
the type of atom, and substances made up of just one type of atom and are known
as elements.
Charges
Electric charge is a property of certain particles, such as electrons, protons,
and quarks that describes how they interact with each other. There are two
different types of electric charge, positive and negative. In general, particles
carrying the same type of charge repel each other, whereas particles carrying
opposite charges attract each other. Within each atom, the protons inside the
nucleus attract the electrons that are outside the nucleus.
You can experience the same attraction and repulsion with magnets. If you place
the north pole of a bar magnet near the south pole of a second bar magnet, you
will find that the magnets attract each other. If you place the same ends next
to each other they will repel each other.
Under normal circumstances, every atom has an equal number of protons and
electrons, and the atom is said to be electrically neutral. The attractive force
between the protons and electrons acts like invisible glue, holding the atoms
together, in much the same way that the gravitational force of the Earth keeps
the moon within sight.
The electrons closest to the nucleus are held to the atom with a stronger force
than the electrons farther from the nucleus. Some atoms hold on to their outer
electrons tightly, while others are a bit more lax. Just how tightly certain
atoms hold on to their electrons turns out to be important when it comes to
electricity.
Conductors and Insulators
Materials such as copper, silver, and aluminum containing loosely bound outer
electrons are called electrical conductors. Copper is a good conductor because
it contains a single loosely bound electron in the outermost reaches of its
electron cloud. Materials that tend to keep their electrons close to home are
classified as electrical insulators. Air, glass, paper, and plastic are good
insulators, as are the rubber-like polymers that are used to insulate electrical
wires.
In conductors, the outer electrons of each atom are bound so loosely that many
of them break free and jump around from atom to atom. If you give these free
electrons a bit of a push in one direction, they will quickly get organized and
move together in the direction of the push.
Creating Current
Electric current, called electricity, is the displacement of a large number of
electrons in the same direction through a conductor when an external force is
applied. That external force is known as voltage.
This flow of electric current appears to happen instantaneously. That is because
each free electron, from one end of a conductor to another, begins to move more
or less immediately, jumping from one atom to the next. So each atom
simultaneously loses one of its electrons to a neighboring atom and gains an
electron from another neighbor. The result of this cascade of jumping electrons
is what we observe as electric current.
The strength of an electric current is defined by how many charge carriers,
electrons, pass a fixed point in one second, and is measured in units called
amperes. One ampere is defined to be \(6.241*10^{18}\). Measuring electric current
is analogous to measuring water flow in gallons per minute. The symbol I is used
to represent the strength of an electric current. You could think of I as the
intensity of the electric current.
You may also hear the term coulomb used to describe the magnitude of the charge
carried by \(6.241*10^{18}\) electrons. A coulomb is related to an amp in that
one coulomb is the amount of charge carried by one amp of current in one second.
Voltage
Electric current is the flow of negatively charged electrons through a conductor
when a force is applied. The force that pushes electrons along is technically
called an electromotive force, but it is more commonly known as voltage. You
measure voltage by using units called volts. Apply enough voltage to a
conductor, provide a complete path through which an electric charge can move,
and the free electrons in the conductor's atoms will move in the same direction.
Think of voltage as electric pressure. In much the same way water pressure
pushes water through pipes and valves, voltage pushes electrons through
conductors. The higher the water pressure, the stronger the push. The higher the
voltage, the stronger the electric current that flows through a conductor.
A voltage is simply a difference in electrical charge between two points. In a
battery, negatively charged atoms build up on one of two metal plates, and
positively charged atoms build up on the other plate, creating a voltage across
the plates. If you provide a conductive path between the metal plates, you
enable excess electrons to travel from one plate to the other, and current will
flow in an effort to neutralize the charges. The electromotive force that
compels current to flow when the circuit is completed is created by the
difference between charges at the battery terminals.
You may also hear the terms potential difference, voltage potential, potential
drop, or voltage drop used to describe voltage. The word potential refers to the
possibility that a current may flow if you complete the circuit, and the words
drop and difference both refer to the difference in charge that creates the
voltage.
Electrical Energy
As electrons travel through a conductor, they transport energy from one end of
the conductor to the other. Because like charges repel, each electron exerts a
non-contact repulsive force on the electron next to it, pushing that electron
along through the conductor. As a result, electrical energy is propagated
through the conductor.
If you can transport that energy to an object that allows work to be done on it,
such as a lightbulb, a motor, or a loudspeaker, you can put that energy to good
use. The electrical energy carried by the electrons is absorbed by the object
and transformed into another form of energy, such as light, heat, or motion.
That is how you make the bulb glow, rotate the motor shaft, or cause the
diaphragm of the speaker to vibrate and create sound.
Electrons
To electrons delivering energy to a light bulb or other device, the word work
has real physical meaning. Work is a measure of the energy consumed by the
device over some time when a force(voltage) is applied to a bunch of electrons
in the device. The more electrons you push, and the harder you push them, the
more electrical energy is available and the more work can be done.
Power(P) is the total energy consumed in doing work over some period of time,
and it is measured in watts(W). Power is calculated by multiplying the
force(voltage) by the strength of the electron flow(current).
\(Power=voltage*current\)
\(P= V * I\)
The power equation is one of a handful of equations that you should really pay
attention to because of its importance in keeping from blowing things up. Every
electronic part, or component, has its limits when it comes to how much power it
can handle. If you energize too many electrons in a given component, you will
generate a lot of heat energy and you might fry that part. Many electronic
components come with maximum power ratings so you can avoid getting into a
heated situation.
Circuits
Electric current does not just flow anywhere. Electrons flow only if you provide
a closed conductive path, known as an electrical circuit for them to move
through, and initiate the flow of a battery or other source of electrical
energy.
Every circuit needs at least three basic things to ensure that electrons get
energized and deliver their energy to something that needs work done.
1. Source of electrical energy: The source provides the voltage, or force, that
nudges the electrons through the circuit.
2. Load: The load is something that absorbs electrical energy in a circuit.
Think of the load as the destination for the electrical energy.
3. Path: A conductive path provides a conduit for electrons to flow between the
source and the load. Copper and other conductors are commonly formed into the
wire to provide this path.
An electric current starts with a push from the source and flows through the
wire path to the load, where electrical energy makes something happen and then
back to the other side of the source. Most often, other electronic parts are
also connected throughout the circuit to control the flow of current.
If you simply provide a conductive path in a closed loop that contains a power
source but no bulb, speaker, or other external load, you still have a circuit
and current will flow. In this case, the role of the load is played by the
resistance of the wire and the internal resistance of the battery, which
transfers the electrical energy into heat energy. Without an external load to
absorb some of the electrical energy, the heat energy can melt the insulation
around a wire or cause an explosion or release of dangerous chemicals from a
battery.
Supplying Electrical Energy
If you take a copper wire and arrange it in a closed loop by twisting the ends
together, do you think the free electrons will flow well? The electrons might
move around a bit, because they are easy to move, but unless a force pushes the
electrons one way or another, you will not get current to flow.
Think about the motion of water that is just sitting in a closed pipe, the water
is not going to go through the pipe on its own. You need to introduce force, a
pressure differential, to deliver the energy needed to get a current flowing
through a pipe. Likewise, every circuit needs a source of electrical energy to
get the electrons flowing. Batteries and solar cells are common sources. The
electrical energy available at your wall outlets may come from one of many
different sources supplied by your power company.
Electrical energy is not created from scratch. It is generated by converting
another form of energy(mechanical, chemical, heat, or light) into electrical
energy. Exactly how electrical energy is generated by your favorite source turns
out to be important because different sources produce different types of
electric current. The two different types are:
1. Direct current(DC): A steady flow of electrons in one direction, with very
little variation in the strength of the current. Cells(batteries) produce DC
and most electronic circuits use DC.
2. Alternating Current(AC): A fluctuating flow of electrons that changes
direction periodically. Power companies supply AC to your electrical outlets.
Direct Current
A battery converts chemical energy into electrical energy through a process
called an electrochemical reaction. When two different metals are immersed in
certain chemicals, the metal atoms react with the chemical atoms to produce
charged atoms, known as ions. Negative ions build up on one metal plate, known
as an electrode. The difference in charge across the two electrodes creates a
voltage. That voltage is the force that electrons need to push them around a
circuit.
You might think that the oppositely charged ions would move toward each other
inside the battery, because opposite charges attract, but the chemicals inside
the battery act as a barrier to prevent this from happening. To use a battery in
a circuit, you connect one side of your load, for instance a light bulb, to the
negative terminal and the other side of your load to the positive terminal. A
terminal is just a piece of metal connected to an electrode to which you can
hook up wires. You have created a path that allows the charges to move, and
electrons flow from the negative terminal, through the circuit, to the positive
terminal. As they pass through the wire filament of the light bulb, some of the
electrical energy supplied by the battery is converted to light and heat,
causing the filament to glow and get warm.
The electrons keep flowing as long as the battery is connected in a circuit and
the electrochemical reactions continue to take place. As the chemicals become
depleted, fewer reactions take place, and the battery's voltage starts to drop.
Eventually, the battery can no longer generate electrical energy, and we say
that the battery is dead.
Because the electrons move in only one direction, from the negative terminal
through the circuit and to the positive terminal, the electric current generated
by a battery is DC. The AAA, AA, C, and D sizes you can buy anywhere each
generate around 1.5 volts. The difference in size among those batteries has to
do with how much current can be drawn, and the longer it will last. Larger
batteries can handle heavier loads, which is just a way of saying they can
provide more power, so they can do more work.
Technically speaking, an individual battery isn't really a battery, it is a
cell. If you connect several cells together, as you often do in flashlights and
toys, then you have created a battery. The battery in your car is made up of six
cells, each generating 2-2.1 volts, connected together to produce 12-12.6 volts
total.
Alternating Current
When you plug a light into an electrical outlet in your home, you are using
electrical energy that originated at a generating plant. Generating plants
process natural resources, like water, coal, oil, natural gas, or uranium,
through several steps to produce electrical energy. Electrical energy is said to
be a secondary energy source because it is generated through the conversion of a
primary energy source.
The electric current generated by power plants fluctuates, or changes direction,
at a regular rate known as the frequency. In the US and Canada, that rate is 60
times a second, or 60 hertz, but in most European countries, AC is generated at
50 Hz. The electricity supplied by your average wall outlet is said to be 120
volts AC, which just means it is alternating current at 120 volts.
Heaters, lamps, hair dryers, and other things are among the electrical devices
that use 120 volts AC directly. Clothes dryers, which require more power, use
240 volts AC directly from a special wall outlet.
Tablets, computers, cellphones, and other electronic devices require a steady DC
supply, so if you are using AC to supply an electronic device or circuit, you
will need to convert AC to DC. Regulated power supplies, known as ac-to-dc
converters, or AC adapters, do not actually supply power, they convert AC to DC
and are commonly included with electronic devices when purchased.
Transforming Light
Solar cells, also known as photovoltaic cells, produce a small voltage when you
shine light on them. They are made from semiconductors, which are materials that
are somewhere between conductors and insulators in terms of their willingness to
give up their electrons. The amount of voltage is produced by a solar cell is
fairly constant, no matter how much light you shine on it. However, the strength
of the current you can draw depends on the intensity of the light. The brighter
the light, the higher the strength of the available current.
Solar cells have wires attached to two terminals for conducting electrons
through circuits, so you can power your calculator or the garden lights that
frame your walkway. Solar panels are becoming increasingly popular for supplying
electrical power to homes and businesses. If you scour the internet you will
find lots of information on how you can make your own solar panels.
Battery Symbols
In the battery symbol, the plus sign signifies the positive terminal(cathode)
and the minus sign signifies the negative terminal(anode). Usually the battery's
voltage is shown alongside the symbol. The sine wave in the symbol for an AC
voltage source is a reminder that the voltage varies up and down. In the symbols
for a photovoltaic cell, the two arrows pointing towards the battery symbol
signify light energy.
Electronics is all about using specialized devices known as electronic
components(switches, resistors, capacitors, inductors, and transistors) to
control current in such a way that a specific function is performed. The nice
thing is that after you understand how a few individual electronic components
work and how to apply some basic principles, you can begin to understand and
build interesting electronic circuits.
Electronic components in your car and audio systems convert electrical energy
into sound energy. In each case, the system's speakers are the load or
destination for electrical energy. The job of the electronic components in the
system is to shape the current flowing to the speakers so that the diaphragm
within each speaker moves in such a way as to reproduce the original sound.
In visual systems, electronic components control the timing and intensity of
light emissions. Many remote control devices, such as the tv remote, emit
infrared light when your press a button, and the specific patterns of the
emitted light acts as a sort of code that is understood by the device you are
controlling. A circuit in your tv detects the infrared light and decodes the
instructions sent by the remote.
Sensing Signals
Electronics can be used to make something happen in response to a specific level
or absence of light, heat, sound, or motion. Electronic sensors generate or
change an electrical current in response to a stimulus.
A common use of electronics is to control the on/off activity and speed of
motors. By connecting various objects to motors, you can use electronics to
control their motion.