Any appliances that we use
in our daily lives such as household appliances, office equipments
and industrial equipments, almost all of those things take electricity.
Therefore, we should understand electricity.
The first question that we
will find out the answer is "where does electricity
come from?"
All matters are made up of
atoms. Then ask the next question, "What are atoms?"
Atoms are the smallest part of an element. They are composed
of nucleus and electrons, electrons surround nucleus. Elements
are identified by the number of electrons in orbit around nucleus
of atoms and by the number of protons in nucleus.
Nucleus is made up of protons and neutrons, and the number of
protons and neutrons are balanced. Neutrons have no electric charge,
protons have positive charges (+) and electrons have negative
charges (-). A positive charge of proton equals a negative charge
of electron.
Electrons are bound in their orbit by attraction of protons, but
electrons in the outer band can become free of their orbit by
some external forces. These are referred to as free electrons,
which move from one atom to the next, electron flows are produced.
These are the basis of electricity. Materials that allow many
electrons to move freely are called conductors
and materials that allow few free electrons to move are called
insulators.
All matters are made up of atoms that have electric charges. Therefore,
they have electric charges. For the matter that has a balanced
the number of protons and electrons, positive charge force and
negative charge force are balanced. It is called neutral state
of an atom. (The number of protons and electrons remains equal.)
"Static electricity"
represents a situation that all things are made up of electric
charges. For example, the rubbing of material against another
can cause the static electricity. Free electrons of one material
move forcefully till they are freed of their orbits around nucleus
and move to another. Electrons of one material decrease, it
presents positive charges. At the same time, electrons of another
increase, it has negative charges.
In general, charge
producing of the matter means the matter has electric charges.
It has positive and negative charges, which is expressed in
coulomb.
Current,
Voltage and Resistance
What is Current? An electrical phenomenon is caused by flow of
free electrons from one atom to another. The characteristics
of current electricity are opposite to those
of static electricity.
Wires are made up of conductors such as copper
or aluminum. Atoms of metal are made up of free electrons, which
freely move from one atom to the next. If an electron is added
in wire, a free electron is attracted to a proton to be neutral.
Forcing electrons out of their orbits can cause a lack of electrons.
Electrons, which continuously move in wire, are called Electric
Current.
For solid conductors, electric current refers to directional
negative-to-positive electrons from one atom to the next. Liquid
conductors and gas conductors, electric current refers to electrons
and protons flow in the opposite direction.
Current is flow of electrons, but current and electron flow in
the opposite direction. Current flows from positive to negative
and electron flows from negative to positive.
Current is determined by the number of electrons passing through
a cross-section of a conductor in one second. Current is measured
in amperes, which is abbreviated "amps".
The symbol for amps is a letter "A".
A current of one amp means
that current pass through a cross-section of two conductors,
which are placed in parallel 1 meter apart with 2x10-7 Newton
per meter force occur in each conductor. It can also mean charges
of one coulomb (or 6.24x1018 electrons) passing through a cross-section
of a conductor in one second.
What is voltage? Electric current is flow of electrons in a conductor. The force
required to make current flow through a conductor is called
voltage and potential is the
other term of voltage. For example, the first element has more
positive charges, so it has higher potential. On the other hand,
the second element has charges that are more negative so it
has lower potential. The difference between two points is called
potential difference.
Electromotive force
means the force which makes current continuously flows through
a conductor. This force can be generated from power generator,
battery, flashlight battery and fuel cell, etc.
Volt, abbreviated "V", is the unit
of measurement used interchangeably for voltage, potential,
and electromotive force. One volt means a force which makes
current of one amp move through a resistance of one ohm.
What is resistance? Electrons move through a
conductor when electric current flows. All materials impede
flow of electric current to some extent. This characteristic
is called resistance. Resistance increases
with an increase of length or decrease of cross-section of a
material.
The unit of measurement for resistance is ohms
and its symbol is the Greek letter omega (Ω).
The resistance of one ohm means a conductor allows a current
of one amp to flow with a voltage of one volt.
All materials are difference in allowing electrons flow. Materials
that allow many electrons to flow freely are called conductors
such as copper, silver, aluminium, hydrochloric solution, sulphuric
acid and saltwater. In contrast, materials which allow few electrons
to flow are called insulators such as plastic,
rubber, glass and dry paper. Another type of materials, semiconductors
have characteristics of both conductors and insulators. They
allow electrons to move while being able to control flow of
electrons and examples are carbon, silicon and germanium, etc.
The resistance of conductor
depends on two main factors as the followings:
The instrument used to measure current
is called ampere meter or ammeter.
•
Steps for current measurement
Connect a small light bulb to a dry cell. Measure current
that passes through light bulb by connecting positive terminal
(+) of ammeter to negative terminal (-) of a dry cell (see
figure)
•
Safety instructions for current measurement;
1.
Estimate current that required measuring
then choose a suitable ammeter, since each ammeter has different
limit of current measurement.
2.
Be sure that the connection to positive terminal
(+) and negative terminal (-) of ammeter are correct.
3.
Do not directly connect ammeter terminals
to dry cell terminals. Since it can damage the meter.
How to measure voltage The instrument used to measure voltage, difference
potential or electromotive force is called voltmeter.
•
Steps for voltage measurement
Connect a small light bulb to a dry cell. A voltmeter is
wired in parallel with the light bulb to measure voltage
across the light bulb. Connect positive terminal (+) of
voltmeter to positive terminal (+) of a dry cell and connect
negative terminal (-) of voltmeter to negative terminal
(-) of a dry cell (see figure).
•
Safety instructions for measuring
voltage;
1.
Estimate voltage that required measuring
then choose
a suitable voltmeter, since each voltmeter is designed with
the limit of voltage measurement.
2.
Be sure that the connecting of positive terminal
(+) and negative terminal (-) of voltmeter are correct.
How to measure resistance The instrument used to measure
resistance is called test meter or multimeter.
The multimeter or test meter is used to make various electrical
measurements such as current, voltage and resistance. It combines
the functions of ammeter, voltmeter and ohmmeter.
•
Steps for resistance measurement
Turn the face dial to a position for required measuring,
resistance, then touch both of terminals of multimeter (see
figure 1) and adjust the meter range to 0 Ω. Touch
both of terminals of meter to a resistance and take the
reading (see figure 2).
Electric current is the ability
to do work. Electric current can be converted to heat, power
and magnetism, to name a few.
Electric current is classified
by its functions and three primary types are:
1.
Heat and power
2.
Electrochemistry
3.
Magnetism
1. Heat and power is used to make heat and power.
For example, current-carrying nichrom wire that nichrom
wire has a high resistance and creates heat. This is applied
to be component of electric ovens, toasters, electric irons
and light bulbs, etc.
Experiment is made by measuring
heat quantity of water by calorimeter. Increase voltage across
wire by the variac and connect ammeter and voltmeter to measure
current and voltage.
Set the variac scale to adjust voltage and current value of
nichrom wire and current is passed through periodically and
measure heat quantity from nichrom wire. There are any indications
of voltage and current. If voltage, current and time increase,
heat quantity will also increase. They are expressed by the
relation as below.
This is called Joule's
law. Heat quantity depends on voltage time current
and interval of time. From Ohm's law, V (Voltage) = I (Current)
x R (Resistance) therefore
Heat quantity depends on
current squared times resistance and interval of time.
When current is passed through nichrom wire in water, current
is converted to heat and temperature rises. Work is done by
heat generated in an electrical circuit, which is called Electric
power.
Electric power is measured
in Watts-hour (Wh) and heat quantity is measured in calories
(Cal).
Work is done by heat generated
in an electrical circuit is written in power, which it means
that the rate work is done in a circuit when 1 Amp flows with
1 Volt applied and its unit of measurement is Watt.
Conclusion
2. Electrochemistry
For example, when current is passed through sodium chloride
(NaCl) solution, a chemical reaction called electrolysis
occurs. This is applied to produce electrolysis, galvanizing
and battery, etc.
Experiment is made by soaking two platinum (Pt) plates
in molten salt. Connect batteries to two platinum plates,
current is passed through molten salt and produces chlorine
bubbles around positive plate (+) and hydrogen bubbles
around negative plate (-) since sodium chloride composes
of sodium (Na) and chloride (Cl). When sodium chloride
melts in water, the elements are separated. Sodium has
positive charges (+), while chlorine has negative charges
(-) and these charges are called ions.
The molten salt has both positive charges, called anodes,
and negative charges called cathodes.
The state of separated elements is called ionization.
If salt is melted by water, solution is available ions,
called electrolyte solution. And if current
is passed through electrolyte solution, a chemical reaction
known as electrolysis occurs.
3. Magnetism
The example of this electric work is a current-carrying
wire, magnetic lines of flux occur. This is applied to produce
electric motors, electric transformers and tape recorders,
etc.
Understanding meaning
of magnetism:
What is magnetism?
The compound formula of magnet is Fe3O4.
All magnets have two characteristics. First, they attract
and hold iron. Secondary, if free to move like the compass
needle, they will assume a north-south position. Any materials
have these characteristics, they are called magnet.
The characteristics of magnet are
•
Every magnet has two poles, one north pole and
one south pole.
•
Opposite poles attract each other, while like
poles repel each other.
Electricity and magnetic field
When magnetic needle is placed near electric wire, which
current is passed through, magnetic needle turns on the
direction of current flow (see figure 1 and 2). Therefore,
electric current flow also produces an associated magnetic
force or it is said that electricity is able to produce
magnetic field.
When magnetic needle is placed in wire coil with one loop
(see figure) and current is passed through wire coil, magnetic
needle turns on the direction as shown in above figure.
And the directions of magnetic lines of flux are shown by
the arrows.
When magnetic needle is placed in wire coil with many loops
as shown in right figure, then current is passed through
coil. The direction of magnetic lines of flux parallels
wire coil. The characteristics of magnetic lines of flux
like the characteristics of magnet, but no magnetic pole.
When a current-carrying wire coil is placed near iron bar,
the iron bar move slightly (see figure 1). If core is placed
in a wire coil, the iron bar is attracted strongly (see
figure 2). Because core is a soft iron, which conducts magnetic
lines of force, when current is passed through wire coil
around core, the core becomes magnetized with high power
that is called electromagnets. This function
is widely applied for using in industries.
English 
