The true cause of electricity was
determined with the development
of the atomic theory of matter.
The presence and motion of
electrons, protons, and other
Manifests itself as attraction,
repulsion, luminous and heating
Scientists could explain electrical
charges when they found atoms were
composed of negatively charged
particles (electrons) orbiting positively
charged particles (protons) and
neutrons which have no charge.
Under most conditions, an atom will
have no charge.
If the number of electrons is increased,
an atom becomes negatively charged.
If electrons are removed, an atom will
have a positive charge.
The force that causes electricity to
move in a conductor is called voltage (V)
or electromagnetic force (E).
Electric potential or potential
difference expressed in volts
Something that moves or tends to
move electricity; the potential
difference derived from an electrical
source per unit quantity of electricity
passing through the source (such as
a cell or generator)
Six Basic Ways to Generate Voltage
• Chemical action
Voltage can be produced by rubbing
two materials together.
Static electricity is the most common
name for electricity generated through
Static electricity occurs frequently in
dry climates or during low humidity.
Voltage can be produced by squeezing
crystals such as natural quartz or
Compressed electrons tend to move
through a crystal at predictable
Crystals are frequently used in
Voltage can be produced by heating the
place where two unlike metals are joined.
The hot junction where the moving
electrons from the metals meet is
called a thermocouple.
A device for measuring temperature
in which a pair of wires of dissimilar
metals (such as copper and iron) are
joined and the free ends of the wires
are connected to an instrument (such
as a voltmeter) that measures the
difference in potential created at the
junction of the two metals
The difference in temperature of the two
metals determines the amount of voltage.
Thermocouples are often used to
measure and regulate temperature,
as in a thermostat.
Voltage can be produced when light
strikes a photosensitive (light-sensitive)
Light dislodges electrons from their
orbits around surface atoms.
Voltage produced in this manner is called
Involving, relating to, or utilizing any
of various electrical effects due to
the interaction of radiation (such as
light) with matter
The photoelectric cell is the device
that operates on this principle.
A plate coated with compounds of
silver or copper oxide, which are
extremely sensitive to light, can also
produce a flow of electrons.
Light is used to generate voltage in
devices requiring extreme precision
such as television cameras and
Voltage can be produced by chemical
reactions, as in a battery cell.
A simple voltaic battery consists of a
carbon strip (positive) and a zinc strip
(negative) suspended in a solution of
water and sulfuric acid.
Since voltage makes current flow in a
closed circuit, work is being done.
Electric power rate
is measured by the
watt - the basic unit
Power is equal to the voltage across
a circuit, multiplied by the current
through the circuit.
Using P as the symbol for electrical
power, the basic power formula is:
P = IE
As an example, when E equals 2 volts
and I equals 2 amperes, P equals
4P = 2E2I
R1 Drawing 1 R1 Drawing 2
20 Ω 20 Ω
I = 2 amps I = 4 amps
E R2 E R2
200 volts 30 Ω 400 volts 30 Ω
50 Ω 50 Ω
In drawing 1, the total voltage is 200 volts. In
drawing 2, the amps were doubled, 2 to 4, thus
resulting in the voltage being 400 volts. When
voltage is doubled and resistance remains
unchanged, power is doubled twice.
Doubling voltage causes a doubling of
current that doubles both of the factors
that determine power.
The rate of change of power, in a
circuit of fixed resistance, is the
square of the change in voltage.
The basic power formula (P = IE)
may also be expressed as:
P = E²/R
P = I²R