After reading this section you will be able to do the following:1. Define electricity and identify the origins of the term.
2. Discuss how electricity can be observed in the world.What is Electricity?Electricity
is a naturally occurring force that exists all around us. Humans have
been aware of this force for many centuries. Ancient man believed that
electricity was some form of magic because they did not understand it.
Greek philosophers noticed that when a piece of amber was rubbed with
cloth, it would attract pieces of straw. They recorded the first
references to electrical effects, such as static electricity and
lightning, over 2,500 years ago.It was not until 1600 that a man
named Dr. William Gilbert coined the term “electrica,” a Latin word
which describes the static charge that develops when certain materials
are rubbed against amber. This is probably the source of the word
“electricity." Electricity and magnetism are natural forces that are
very closely related to one another. You will learn a little about
magnetism in this section, but there is a whole section on magnetism if
you want to learn more.In order to really understand electricity, we need to look closely at the very small components that compose all matter.Review Electricity occurs naturally and has been observed for thousands of years.Electricity and magnetism are very closely related.ELECTRIC CHARGE
After reading this section you will be able to do the following:
Explain the differences between electrons and protons.
Predict what happens when protons and electrons interact with other protons or electrons.Electrons 
Electrons
are the smallest and lightest of the particles in an atom. Electrons
are in constant motion as they circle around the nucleus of that atom.
Electrons are said to have a negative charge, which means that they seem
to be surrounded by a kind of invisible force field. This is called an
electrostatic field.ProtonsProtons are much larger and heavier than electrons. Protons have a positive electri
cal
charge. This positively charged electrostatic field is exactly the same
strength as the electrostatic field in an electron, but it is opposite
in polarity. Notice the negative electron (pictured at the top left) and
the positive proton (pictured at the right) have the same number of
force field lines in each of the diagrams. In other words, the proton is
exactly as positive as the electron is negative.
Like charges repel, unlike charges attract
Two
electrons will tend to repel each other because both have a negative
electrical charge. Two protons will also tend to repel each other
because they both have a positive charge. On the other hand, electrons
and protons will be attracted to each other because of their unlike
charges.
Since the electron is much smaller and lighter than a
proton, when they are attracted to each other due to their unlike
charges, the electron usually does most of the moving. This is because
the protons have more mass and are harder to get moving. Although
electrons are very small, their negative electrical charges are still
quite strong. Remember, the negative charge of an electron is the same
as the positive electrical charge of the much larger in size proton.
This way the atom stays electrically balanced.
Another important
fact about the electrical charges of protons and electrons is that the
farther away they are from each other, the less force their electric
fields have on each other. Similarly, the closer they are to each other,
the more force they will experience from each other due to this
invisible force field called an electric field.
Review
Electrons have a negative electrostatic charge and protons have a positive electrostatic charge.
A good way to remember what charge protons have is to remember both proton and positive charge start with "P."
Like charges repel, unlike charges attract, just like with magnets.
ELECTRICAL CURRENT
After reading this section you will be able to do the following:
Explain how an electrical current is produced.
Electricity
is a term used to describe the energy produced (usually to perform
work) when electrons are caused to directional (not randomly) flow from
atom to atom. In fact, the day-to-day products that we all benefit from,
rely on the movement of electrons. This movement of electrons between
atoms is called electrical current. We will look at how electrical
current is produced and measured in the following pages.
Review
Electricity is a word used to describe the directional flow of electrons between atoms.
The directional movement of electrons between atoms is called electrical current.
CONDUCTORS AND INSULATORS
After reading this section you will be able to do the following:
Contrast the characteristics of conductors and insulators.
List examples of common conductors and insulators.
Explain how insulators provide protection from electricity.
In
the previous pages, we have talked a bit about “conductors” and
“insulators”. We will discuss these two subjects a little more before
moving on to discuss circuits.
Conductors
Do
you remember the copper atom that we discussed? Do you remember how its
valence shell had an electron that could easily be shared between other
atoms? Copper is considered to be a conductor because it “conducts” the
electron current or flow of electrons fairly easily. Most metals are
considered to be good conductors of electrical current. Copper is just
one of the more popular materials that is used for conductors.
Other
materials that are sometimes used as conductors are silver, gold, and
aluminum. Copper is still the most popular material used for wires
because it is a very good conductor of electrical current and it is
fairly inexpensive when compared to gold and silver. Aluminum and most
other metals do not conduct electricity quite as good as copper.
Insulators
Insulators
are materials that have just the opposite effect on the flow of
electrons. They do not let electrons flow very easily from one atom to
another. Insulators are materials whose atoms have tightly bound
electrons. These electrons are not free to roam around and be shared by
neighboring atoms.
Some common insulator materials are glass, plastic, rubber, air, and wood.
Insulators
are used to protect us from the dangerous effects of electricity
flowing through conductors. Sometimes the voltage in an electrical
circuit can be quite high and dangerous. If the voltage is high enough,
electric current can be made to flow through even materials that are
generally not considered to be good conductors. Our bodies will conduct
electricity and you may have experienced this when you received an
electrical shock. Generally, electricity flowing through the body is not
pleasant and can cause injuries. The function of our heart can be
disrupted by a strong electrical shock and the current can cause burns.
Therefore, we need to shield our bodies from the conductors that carry
electricity. The rubbery coating on wires is an insulating material that
shields us from the conductor inside. Look at any lamp cord and you
will see the insulator. If you see the conductor, it is probably time to
replace the cord.
Recall our earlier discussion about
resistance. Conductors have a very low resistance to electrical current
while insulators have a very high resistance to electrical current.
These two factors become very important when we start to deal with
actual electrical circuits.
Review
Conductors conduct electrical current very easily because of their free electrons.
Insulators oppose electrical current and make poor conductors.
Some common conductors are copper, aluminum, gold, and silver.
Some common insulators are glass, air, plastic, rubber, and wood.
AMPERAGEAfter reading this section you will be able to do the following:
Define amperes and name the instrument that is used to measures amperage.
Construct an experiment to determine the amount of amps flowing in a circuit.
It
is very important to have a way to measure and quantify the flow of
electrical current. When current flow is controlled it can be used to do
useful work. Electricity can be very dangerous and it is important to
know something about it in order to work with it safely. The flow of
electrons is measured in units called amperes.
The term amps is often used for short. An amp is the amount of electri
cal
current that exists when a number of electrons, having one coulomb
(ku`-lum) of charge, move past a given point in one second. A coulomb is
the charge carried by 6.25 x 10^18 electrons. 6.25 x 10^18 is
scientific notation for 6,250,000,000,000,000,000. That is a lot of
electrons moving past a given point in one second!
Since
we cannot count this fast and we cannot even see the electrons, we need
an instrument to measure the flow of electrons. An ammeter is this
instrument and it is used to indicate how many amps of current are
flowing in an electrical circuit.
Review
Amperage is a term used to describe the number of electrons moving past a fixed point in a conductor in one second.
Current is measured in units called amperes or amps.
VOLTAGEAfter reading this section you will be able to do the following:
1. Define EMF and explain how it is measured.
2. Explain why EMF is important to the flow of electrical current.
3. List several examples of sources of electromotive force.
We
also need to know something about the force that causes the electrons
to move in an electrical circuit. This force is called electromotive
force, or EMF. Sometimes it is convenient to think of EMF as electrical
pressure. In other words, it is the force that makes electrons move in a
certain direction within a conductor.
But how do we
create this “electrical pressure” to generate electron flow? There are
many sources of EMF. Some of the more common ones are: batteries,
generators, and photovoltaic cells, just to name a few.
Batteries
are constructed so there are too many electrons in one material and not
enough in another material. The electrons want to balance the
electrostatic charge by moving from the material with the excess
electrons to the material with the shortage of electrons.
However, they cannot because there is no conductive path for them to travel.
However,
if these two unbalanced materials within the battery are connected
together with a conductor, electrical current will flow as the electron
moves from the negatively charged area to the positively charged area.
When you use a battery, you are allowing electrons to flow from one end
of the battery through a conductor and something like a light bulb to
the other end of the battery. The battery will work until there is a
balance of electrons at both ends of the battery. Caution: you should
never connect a conductor to the two ends of a battery without making
the electrons pass through something like a light bulb which slows the
flow of currents. If the electrons are allowed to flow too fast the
conductor will become very hot, and it and the battery may be damaged.
We
will discuss how electrical generators use magnetism to create EMF in a
coming section. Photovoltaic cells turn light energy from sources like
the sun into energy. To understand the photovoltaic process you need to
know about semiconductors so we will not cover them in this material.
How does the amp and the volt work together in electricity?
To
understand how voltage and amperage are related, it is sometimes useful
to make an analogy with water. Look at the picture here of water
flowing in a garden hose. Think of electricity flowing in a wire in the
same way as the water flowing in the hose. The voltage causing the
electrical current to flow in the wire can be considered the water
pressure at the faucet, which causes the water to flow. If we were to
increase the pressure at the hydrant, more water would flow in the hose.
Similarly, if we increase electrical pressure or voltage, more
electrons would flow in the wire.
Does it also make sense that if we
were to remove the pressure from the hydrant by turning it off, the
water would stop flowing? The same is true with an electrical circuit.
If we remove the voltage source, or EMF, no current will flow in the
wires.
Another way of saying this is: without EMF, there will be no
current. Also, we could say that the free electrons of the atoms move in
random directions unless they are pushed or pulled in one direction by
an outside force, which we call electromotive force, or EMF.
Review
EMF is electromotive force. EMF causes the electrons to move in a particular direction.
EMF is measured in units called volts.
RESISTANCE
After reading this section you will be able to do the following:
Define resistance and how we measure it.
Discuss the similarities between resistance in a wire and the resistance in a water hose.
There
is another important property that can be measured in electrical
systems. This is resistance, which is measured in units called ohms.
Resistance is a term that describes the forces that oppose the flow of
electron current in a conductor. All materials naturally contain some
resistance to the flow of electron current. We have not found a way to
make conductors that do not have some resistance.
If we
use our water analogy to help picture resistance, think of a hose that
is partially plugged with sand. The sand will slow the flow of water in
the hose. We can say that the plugged hose has more resistance to water
flow than does an unplugged hose. If we want to get more water out of
the hose, we would need to turn up the water pressure at the hydrant.
The same is true with electricity. Materials with low resistance let
electricity flow easily. Materials with higher resistance require more
voltage (EMF) to make the electricity flow.
The scientific definition
of one ohm is the amount of electrical resistance that exists in an
electrical circuit when one amp of current is flowing with one volt
being applied to the circuit.
Is resistance good or bad?
Resistance
can be both good and bad. If we are trying to transmit electricity from
one place to another through a conductor, resistance is undesirable in
the conductor. Resistance causes some of the electrical energy to turn
into heat so some electrical energy is lost along the way. However, it
is resistance that allows us to use electricity for heat and light. The
heat that is generated from electric heaters or the light that we get
from light bulbs is due to resistance. In a light bulb, the electricity
flowing through the filament, or the tiny wires inside the bulb, cause
them to glow white hot. If all the oxygen were not removed from inside
the bulb, the wires would burn up.
An important point to mention here
is that the resistance is higher in smaller wires. Therefore, if the
voltage or EMF is high, too much current will follow through small wires
and make them hot. In some cases hot enough to cause a fire or even
explode. Therefore, it is sometimes useful to add components called
resistors into an electrical circuit to slow the flow of electricity and
protect of the components in the circuit.
Resistance is also good
because it gives us a way to shield ourselves from the harmful energy of
electricity. We will talk more about this on the next page.
Review
Resistance is the opposition to electrical current.
Resistance is measured in units called ohms.
Resistance is sometimes desirable and sometimes undesirable.
AC THEORY: Combining Alternating Currents.
AC THEORY: Voltage and Current for R.For
the parallel AC circuit the voltage is common across all current
branches of R, C and L. However, the current for each branch will have a
phase angle determined by the resistive, capacitive or inductive
element of that component.
