# Presentation - Career and Technical Education

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24 Νοε 2013 (πριν από 4 χρόνια και 5 μήνες)

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MODULE 4:

ELECTRICAL SYSTEMS

Engineering Mathematics

Introduction

2

The Electrical Systems lesson will cover
electricity, Ohm’s Law, measuring, and
efficiency. You will determine a 6
-
volt
battery current, voltage, and resistance.

Student teams
will perform an energy
audit of their
school.

In
you
will design a
building/wing/floor that meets a certain
power consumption
criteria,
using
conventional power sources (fossil fuels)
and renewable power sources.

Chapter 4: Outline

3

1.
Ohm’s Law, Power and DC

2.
Serial vs. Parallel, Capacitors, and
Inductors

3.
AC Circuits

4.
Transformers and Motors

Objectives and Results

4

Students will understand the meaning of electricity,
Ohm’s Law, and the meaning of electrical systems.

Students will understand the different types of electrical
systems, as well as the careers and educational
opportunities available in the electrical systems industry.

Student teams will perform an energy audit of their
school and design a building/wing/floor that meets a
certain power consumption criteria, using conventional
power sources (fossil fuels) and renewable power
sources.

Schedule of Assignments

5

Class/Week

Topic

Assignment

1
-
2

Introduction

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Vo捡b畬u特

††
䕬散瑲楣i氠

Engineering

O*Net

Chapter 4.1

#1
-
Individual

Write a one
-
Electrical Engineering
Occupation.

3
-
10

Ohm’s Law

Chapter 4.2, 4.3

#2 In teams of 2
-
3, complete
the Ohm’s Law Exercise
.

11
-
20

Energy Audit

Chapter 4.4

#3 In teams of 2
-
3, complete
the Electrical Systems
Project (Energy

Audit).

Vocabulary

6

Electrical Systems

Ohm’s Law

Motor

Electrical Power

Efficiency

Electrical Engineering

There are several career opportunities in the
electrical systems field.

Electrical engineering
is the
branch
of engineering
that deals with the technology of electricity,
especially the design and application of circuitry
and equipment for power generation and
distribution, machine control, and communications.

7

Careers/Educational Opportunities

Career and educational opportunities choices include
the following:

Electrical engineers

Electrical engineering technicians

Electrical engineering technologists

Electricians

Electrical and electronic equipment assemblers

Electronics engineering technologists

8

Electrical Engineering Assignment

9

Visit the O*Net website (
www.onetonline.org
).

Write a one
-
page essay on the electrical
engineering profession.

Discuss at least one sub
-
specialty of electrical

Use the O*Net website and at least one other
primary source.

Electrical Systems

The

electrical

systems

lesson

consists

of

seven

sections
:

What

is

Electricity?

What

is

Ohm’s

Law?

What

are

Electrical

Systems?

Types

of

Electrical

Systems

Careers

and

Educational

Opportunities

Ohm’s

Law

Exercise

Electrical

Systems

Project

10

What is Electricity?

Electricity

was not
'invented.”
I
ts
characteristics and
uses have been known about and developed over
hundreds of years
.

Electricity
is a form of energy involving the flow of
electrons.

All

matter

is

up

of

atoms,

and

an

atom

has

a

center,

called

a

nucleus
.

11

What is Electricity?, cont.

The
nucleus contains positively charged particles
called protons and uncharged particles called
neutrons. The nucleus of an atom is surrounded by
negatively charged particles called electrons
.

The negative charge of an electron is equal to the
positive charge of a proton, and the number of
electrons in an atom is usually equal to the number
of protons.

12

Electric Current

When
the balancing force between protons and
electrons is upset by an outside force, an atom may
gain or lose an electron
.

When
electrons are "lost" from an atom, the free
movement of these electrons constitutes an
electric
current
.

13

What is Ohm’s Law?

14

When

a

voltage

is

applied

to

a

circuit

containing

only

resistive

elements

(i
.
e
.
,

no

coils),

current

flows

according

to

Ohm's

Law
,

which

is

shown

below
.

What is Ohm’s Law?, cont.

15

Where

I = Electrical
Current
(amperes),

V
=
Voltage (volts), and

R = Resistance
(ohms).

Ohm’s Law is used to determine the
electric current
in
electrical systems.

What is Ohm’s Law?, cont.

16

Therefore,
if the voltage is increased, the current will
increase provided the resistance of the circuit does
not change
.

Similarly
, increasing the resistance of the circuit will
lower the current
flow,
if the voltage is not changed
.

The
formula can be reorganized so that the
relationship can easily be seen for all of the three
variables.

What are Electrical Systems?

Electrical systems
are
utilities that
provide
electricity.

They
are groups of electrical components connected
to carry out some operation
.

For example, an
electrical system
may be
equipment
in a motor vehicle that provides electricity
to start the engine and ignite the fuel and operate
the lights and windshield wiper and heater and air
conditioner and

17

Electric Motors

Electric
motors
involve rotating coils of wire which
are driven by the magnetic force exerted by a
magnetic field on an electric current.

They
transform electrical energy into mechanical
energy
.

There are two types of motors:
DC
and

AC
.

The abbreviations
AC

and
DC
are often used to
mean simply alternating and direct, as when they
modify current or
voltage.

18

DC and AC Motors

19

DC Motors

A
DC
motor
is an electric motor that runs on direct
current (DC) electricity
.

In direct current (
DC
, also
dc
), the flow of electric
charge is only in one direction
.

DC motors
are
used to run machinery, often
eliminating the need for a local steam engine or
internal combustion engine.

20

DC Motors, cont.

DC
motors

can operate directly from rechargeable
batteries, providing the motive power for the first
electric vehicles.

Today,
DC
motors

are still found in applications as
small as toys and disk
drives
or in large sizes to
operate steel rolling mills and paper
machines.

Modern
DC
motors

are nearly always operated in
conjunction with power electronic devices.

21

DC Motor Operation

22

AC Motor

An

AC
motor

is an electric motor that is driven
by an alternating current.

In

alternating current (AC,
also

ac),
the
movement of electric charge periodically
reverses direction.

In direct current (
DC
, also
dc
), the flow of
electric charge is
only in one direction
.

23

AC Power

AC
is the form in which electric power is delivered to

The
usual waveform of an
AC
power circuit is a sine
wave.

An electric motor that operates on
alternating
current,
like the
kind of power source found in a
household outlet.

24

AC Motor Operation

25

Ohm’s Law Exercise

In
this
practice exercise, you will build
a one
-
battery,

one
-
resistor
circuit.

You will use Ohm’s Law to calculate the power and
measure efficiency.

You

will

learn

to

use

the

following

items
:

Voltmeter

Ammeter

Ohmmeter

Ohm's

Law

26

Project Team Protocol

Form teams of 2
-
3 students.

Random selection

Teacher choice

Student choice

Student teams will complete
and assign roles with their
teams.

27

Materials:
Ohm’s Law Exercise

The

team’s

materials

will

gather

the

parts

and

materials

listed

below
:

Calculator

(or

pencil

and

paper

for

doing

arithmetic)

6
-
volt

battery

Assortment

of

resistors

between

1
k
Ω

and

100
k
Ω

in

value

28

Procedures: Ohm’s Law Exercise

The
resistance values
are between
1
k
Ω

and 100
k
Ω

for the sake of obtaining accurate voltage and current

With
very low resistance values, the internal resistance
of the ammeter has a significant impact on
measurement accuracy.

29

Procedures: Ohm’s Law
Exercise, cont.

Very high resistance values can cause problems for
voltage measurement, the internal resistance of the
voltmeter substantially changing circuit resistance
when it is connected in parallel with a high
-
value
resistor.

At
the recommended resistance values, there will
still be a small amount of measurement error due to
the "impact" of the meter, but not enough to cause
serious disagreement with calculated values.

30

Ohm’s
Law Exercise

SCHEMATIC
DIAGRAM

31

Procedures: Ohm’s Law Exercise

32

Instructions:
Ohm’s Law Exercise

1.
Select
a resistor from the assortment, and measure
its resistance with your multimeter set to the
appropriate resistance range.

2.
Be
sure not to hold the resistor terminals when
measuring
resistance
-
to
-
hand
body resistance will influence the measurement!

3.
Record
this resistance value for future use.

33

Instructions:
Ohm’s Law
Exercise, cont.

4.
Build
a one
-
battery, one
-
resistor circuit. A terminal
strip is shown in the illustration, but any form of
circuit construction is okay.

5.
Set
your multimeter to the appropriate voltage
range and measure voltage across the resistor as it

6.
Record
this voltage value along with the resistance
value previously measured.

34

Procedures: Ohm’s Law
Exercise, cont.

7.
Set
your multimeter to the highest current range
available. Break
the circuit and connect the
ammeter within that break, so it becomes a part of
the circuit, in series with the battery and resistor.

8.
Select
the best current range: whichever one gives
the strongest meter indication without over
-
ranging
the meter. If your multimeter is
auto
-
ranging
, of
course, you need not bother with setting ranges.

9.
Record
this current value along with the resistance
and voltage values previously recorded.

35

Procedures: Ohm’s Law
Exercise, cont.

10.
Taking
the measured figures for voltage and
resistance, use the Ohm's Law equation to calculate
circuit current. Compare this calculated figure with
the measured figure for circuit current:

36

Procedures: Ohm’s Law
Exercise, cont.

11.
Taking
the measured figures for voltage and
current, use the Ohm's Law equation to calculate
circuit resistance. Compare this calculated figure
with the measured figure for circuit
resistance:

37

Procedures: Ohm’s Law
Exercise, cont.

12.
Finally
, taking the measured figures for resistance
and current, use the Ohm's Law equation to
calculate circuit voltage. Compare this calculated
figure with the measured figure for circuit voltage:

38

V = I x R

Procedures: Ohm’s Law
Exercise, cont.

13.
There
should be close agreement between
all
measured
and all calculated figures. Any
differences in respective quantities of voltage,
current, or resistance are most likely due to meter
inaccuracies. These differences should be rather
small, no more than several percent. Some meters,
of course, are more accurate than others!

39

Procedures: Ohm’s Law
Exercise, cont.

14.
Substitute
different resistors in the circuit and re
-
take all resistance, voltage, and current
measurements. Re
-
calculate these figures and
check for agreement with the experimental data
(measured quantities). Also note the simple
mathematical relationship between changes in
resistor value and changes in circuit current.
Voltage should remain approximately the same for
any resistor size inserted into the circuit, because it
is the nature of a battery to maintain voltage at a
constant level.

40

Electrical Systems Project

Design Challenge

Student teams will perform an energy
audit of
their
school.

In
you will design a
building/wing/floor
that meets a certain power consumption
criteria,
using conventional power sources (fossil fuels) and
renewable power sources.

41