Electrical Principles
Chapter 2
Energy, Voltage, Voltage Types,
AC/DC, Current, Power,
Restrictive Circuits, Inductive
Circuits, Resistance, Heat, and
Light
Energy
Energy
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Energy – Is the capacity to do work.
There are two types of Energy – Potential
and Kinetic.
Potential Energy – Stored Energy.
Example: Battery.
Kinetic Energy – Energy in motion.
Kinetic Energy is released Potential
Energy. Example: Battery operated
electric motor.
Energy

Consumed Energy : Sources of Energy
that once used can not be replaced.
Example: Coal, Oil, Fossil Fuels.

Renewable Energy : Solar, Wind, Water,
Thermal Sources, Wood.
Voltage
Voltage

Voltage: Is the amount of electrical
pressure in a circuit.
Pressure
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Voltage is measured in Volts (V).
Voltage is also known as ElectroMotive
Force (EMF) or Potential Difference.
Voltage
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Voltage is produced any time there is an
excess of electrons at one terminal of a
Voltage source and a deficiency of
electrons at the other terminal.
Voltage may be produced by
electromagnetism (generators), chemicals
(batteries), light (photocells or solar cells),
heat (thermocouples – Nuclear power),
pressure (pizioelectricity – electronic drum
pads), or friction (static electricity).
Voltage
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Amount of Voltage in a circuit depends on
the application. Example: IPODs require
one or two batteries.
Two types of Voltage – Alternating
Current (AC) and Direct Current (DC).
Alternating Current (AC) – Voltage that
reverses its direction of flow at regular
intervals (Two steps forward – One step
back). Most common type of voltage.
Voltage

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Direct Current (DC) – Flows in one
direction depending upon Polarity of
circuit. All points in a DC circuit has
Polarity.
Polarity – Is the positive (+) or negative (-)
state of an object.
Rectifier : AC current can be changed to
DC current by passing the AC current
through a Rectifier. Example: Power
Chargers for Cell Phones are AC/DC
Rectifiers.
Current
Current

Current (I) flows through a circuit when a
source of power is connected to a device
that uses electricity.
Current


Current (I) is the amount of electrons
flowing through an electrical circuit.
Current (I) is measured in Amperes (A).
Current

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
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An Ampere is the number of electrons
passing a given point in one second.
The more power a load requires, the larger
the amount of Current flow.
Current may be direct (DC) or alternating
(AC).
Two types of Current Flow –
Conventional Current Flow and
Electron Current Flow.
Current

Conventional
Current Flow is
current flow from the
positive (+) to
negative (-).

Electron Current
Flow is current flow
from the negative (-)
to positive (+).
Power
Power


Power (P) is the rate of doing work or using
energy.
Power may be expressed as True Power
(P ) or Apparent Power (P ).
True Power (P ) is the actual power used
in an electrical circuit.
Apparent Power (P ) is the product of the
voltage and current in a circuit calculated
without considering the phase shift that
may be present between the voltage and
the current in the circuit.
T


A
T
A
Power

True Power is expressed in Watts (W).
P=W
Apparent Power is expressed in Volt
Amps (VA). P =VA.
P is always less than P in any circuit in
which there is a phase shift between
voltage and current.
T

A

T
A
Power

Phase Shift is
the state when
voltage and
current in a
circuit do not
reach their
maximum
amplitude and
zero level at the
same time.
Power


Restrictive Circuit is a
circuit that contains only
resistance.
In-phase is the state
when voltage and current
reach their maximum
amplitude and zero level at
the same time.
Power
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Inductance is the property of an electric
device that opposes a change in current
due to its inability to store energy in a
magnetic field.
Inductive Circuit is a circuit in which
current lags voltage.
Capacitance is the ability to store energy
in the form of an electrical charge.
Power


Capacitive Circuit is a circuit in which
current leads voltage. The greater the
Capacitance in a circuit, the larger the
phase shift.
Power Factor is the ratio of true power
used in an AC circuit to apparent power
delivered to the circuit.
Power


Resistance (R) is the opposition to current
flow. Resistance is measured in Ohms
(Ώ). Resistance limits the flow of current
in an electrical circuit.
Conductors are made of materials that
have very little resistance and permits
electrons to move through it easily.
Power

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Insulators are made of a material that has
a very high resistance and resists the flow
of electrons.
Heat is thermal energy. Electrical energy
may be converted to heat.
British Thermal Units (BTU) or Calories
are used to measure heat.
Power


One BTU is the amount of heat required to
raise the temperature of 1 lb of water 1
degree Fahrenheit.
One Calorie is the amount of heat
required to raise 1gram of water 1 degree
celcius.
Power

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Thermal Conductivity is the property of a
material to conduct heat in the form of thermal
energy.
Heat Sink is a device that conducts and
dissipates heat away from a component.
HEAT kills electronics.
Light is that portion of the electromagnetic
spectrum which produces radian energy.
Lumen (lm) is the unit used to measure the total
amount of light produced by a light source.
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