Download Devices and systems convert energy with varying efficiencies

Chapter 3
Section 3.1

What is energy?

Where do we use energy?

How do we convert one type of energy into
another?

Energy is defined as the ability to do work
 It can cause changes to the temperature, shape,
speed, or direction of an object
 http://www.youtube.com/watch?v=pDK2p1QbPK
Q

There are four common types of energy:
 Chemical
 Electrical
 Mechanical
 Thermal

The energy stored in
chemicals

This is a form of
potential or stored
energy

It is released when
chemicals react

A common molecule used for the production of
energy in humans is glucose, a type of sugar

Your cells use glucose molecules and a series of
chemical reactions to convert the chemical
energy stored in glucose into thermal and
mechanical energy

Chemical energy from batteries can be
converted to electricity and then sound

Part of the mechanical
energy used to
demolish this building
came from the
chemical energy stored
in explosives

The rest comes from
gravitational potential
energy

The energy of charged
particles

Electrical energy is
transferred when
electrons travel from
one place to another

The energy possessed
by an object because of
its motion or its
potential to move

A thrown baseball has
mechanical energy
because of its
movement and its
potential to fall

Potential Energy
 Stored energy that can
be converted to other,
useful forms

Kinetic Energy
 Energy due to motion

http://www.youtube.com/watch?v=7K4V0NvUxRg

The total kinetic
energy of all the
particles in a substance

The faster a particle
moves, the more
kinetic energy it has;
this also means it has
more thermal energy
(heat)

You can use various
devices to transform
electricity into other
forms of energy

Electricity can be
transformed into any
other type of energy,
such as heat, light,
sound, or movement
(mechanical energy)

A thermocouple is a device that can convert thermal
energy into electrical energy

It consists of two different metals joined together that
conduct heat a slightly different rates

When the metals are heated, this different results in
electricity flowing from one metal to the other

http://www.youtube.com/watch?v=gtO0kQ-PT_0 (1
min)

Devices such as heaters and ovens do the
opposite of a thermocouple; they convert
electrical energy into thermal energy

The electrons flow through a metal and heat
up the metal, releasing heat
Examples :
Device
Energy Conversion
Stove Burner
Hair Dryer
Starting form
Electricity
Electricity
Light Bulb
Loud Speaker
Electric Car
Solar Cell
Generator
Battery
Thermocouple
Electricity
Electricity
Electricity
Light
Mechanical
Chemical
Thermal
Final Form
Thermal
Thermal/Mech/
Sound
Light/Thermal
Sound
Mechanical
Electricity
Electricity
Electricity
Electricity

C+R Pg. 323
 #1-9
Section 3.2

Many of the electrical devices we use
everyday contain a motor

This important energy converter can be
traced back to the early 1800s
 In 1820 Hans Christian Oersted discovers that
current flowing through a wire creates a magnetic
field around the wire

Later on, Michael Faraday constructs a device
which uses electromagnetic forces to move
an object
 This was effectively the first motor
▪ It didn’t work very well, nor did it produce a lot of power,
but it showed that electricity could produce continuous
motion

http://www.youtube.com/watch?v=zOdboRY
f1hM

Running electric current through a wire
creates a magnetic field. Using this simple
principle, many useful devices, such as motor
and stereo speakers have been developed.

The magnetic field around a wire is circular
and continuous

In a piece of wire, the
magnetic field
generated does not
become particularly
strong

If the wire is coiled
around an object (such
as a nail), the lines of the
magnetic field overlap
and the overall field
becomes much stronger

The more wraps, the more overlapping, and the
stronger the magnetic field

The nail becomes an electromagnet when
current runs through the wire

The stronger the magnetic field, the stronger
the magnet

However, when the electric current is stopped,
the magnetic field collapses, and all magnetic
attraction is lost

An electric motor uses
electric energy to make a coil
of wire spin between the
poles of a magnet (the “field
magnet”).

This occurs because the coil
(armature), is connected to a
source of electric energy.

Current flowing through the
coil turns into an
electromagnet, which is
rotated by magnetic forces
from the field magnet.

https://www.youtube.com/watch?v
=LAtPHANEfQo

The fundamental law of all magnetsopposite poles attract and like poles repel- is
the basis upon which electric motors
function.

In one common design
for direct current (DC),
a rotating wire coil
(armature) becomes an
electromagnet as
current flows into it
through a split ring
commutator

The armature is
attracted and repelled by
stationary field magnets
near it, so it begins to
rotate.

The commutator acts as
a switch, cutting off then
reversing the direction of
current flow to keep the
Direct Current (DC) - electricity
armature turning.
flows in only one direction.
https://www.youtube.com/watch?v=BcIDRet7
87k

Alternating Current (AC) electricity flows back and
forth 60 times per second.

Large electric generators in
power stations produce
alternating current for us in
homes and industry.

Transformers are used to
“step up” the voltage for
efficient transmission over
long distances.

Electric currents can produce magnetic
effects.

The opposite process is also possible.

Electric effects can be produced using a
magnet. Michael Faraday and an American
scientist named Joseph Henry made this
discovery in 1831.

Working independently, they found that a
voltage developed in wires that were moved
at an angle to a nearby magnet.

The same thing happened when the magnet
is moved at an angle to a stationary wire.

This process is know as electromagnetic
induction.
Joseph Henry
1797 - 1878

Electric generators use
the relationship between
magnetic fields and
electric charges to cause
charges to move.

Any moving electric
charge generates a
magnetic field, and any
moving magnetic field
also causes the
movement of an electric
charge.

Within a generator, a series of magnets is
connected to a turbine driven by some other
energy source (wind, flowing water, steam, etc.)

The magnets in the generator spin relative to a
coil of conducting wires.

The current then leaves the generator to be used
by devices connected to it or it enters the power
grid for distribution to a wider area.

C+R Pg. 331
 #2-7, 9-10
Section 3.3

We use energy in every aspect of our lives
 At home, in our vehicle, at school, etc.

How do we know which type of energy is
best?

How do we know what machines convert
energy the best?

Power is the rate at which energy is
transferred or transformed

Power tells you how fast the energy is being
used or produced

If a machine uses 1 Watt of power, it uses one
joule of energy in one second

For example, an electric hair dryer that uses
1500 joules of energy every second would be
rated at 1500 watts.

A light bulb that uses 60 joules of energy
every second would be rated at 60 watts.

A generator produces 60 J of electric energy
in thirty seconds. How many watts of power
does it produce?

Skills Practice

What do you buy from power companies?
 Electric energy

The consumption of electric energy is
measured in watts. Usually, when you use
power you are using it over an extended
period of time
 Energy = power x time (W•h)

Watt Hours
 How much electric energy does a 40 W light bulb
use if it is left on for two hours?

Skills Practice

The watt hour is a small unit of energy

Electric utility companies use a unit of energy
1000x larger, the kW•h

1 kW•h = 1000 W•h

(Epcor Bill!)

A small kettle is rated at 1000 watts. This
means that it uses 1000 watts for each hour it
is used. During one week, it is used for two
hours. How much energy does it use in
kilowatt hours?

Skills Practice

How do we calculate the power across the
resistor?
 Step 1. Ohms law to find the Current.
 Step 2. P = V x I

What do you already know about energy?

What types of energy are produced by a blow dryer?






Thermal energy
Mechanical energy
Sound energy
Light energy
Friction produces thermal energy that is wasted
If you measured the electric energy that goes into the
dryer, and compare it to ALL the forms of output
energy, you would find that they are equal

Energy cannot be
created or destroyed; it
can only be transformed
from one type to
another

Energy does not just
disappear, if some
energy seems to be
missing it is because
some of it was dissipated
to the surroundings
Input
Energy
Output
Energy
What
goes
in
Must
come
out

Most often the missing energy is lost or
dissipated as heat

Mechanical systems dissipate energy to their
surroundings, and all the “missing” energy is
transformed into energy you cannot use

Incandescent light bulbs are designed to convert
electric energy into light
 Incandescent means “glowing with heat”

These bulbs produce light when electricity flowing
through a wire makes the wire hot

Some electricity is converted to light, most of it is
converted to other types of energy, such as heat

http://www.youtube.com/watch?v=ByCOTG2-mhg

Efficiency is a measure of how completely
input energy is converted to output energy

Incandescent bulbs and fluorescent bulbs
produce about the same amount of light;
however, incandescent bulbs produce much
more heat, which is wasted

Therefore, incandescent light bulbs are much
less efficient than fluorescent bulbs

An electric kettle uses input energy of 240
000 joules to heat water. 196 000 J is actually
used to heat the water. Calculate the
efficiency of the kettle.

Skills Practice

C+R Pg. 338
 #1-10
Section 3.4

Devices, which have an energy-efficient
design, are an important consideration for
the consumer, because these devices use less
electricity.

Energy costs money and it also affects the
environment, so reducing energy
consumption is a good practice.

Electric heaters come very close to being
100% efficient, but devices that convert
electricity to other forms can never be 100%
efficient.

Some energy is lost, or dissipated in a form
that is not useful output.

Friction causes thermal energy to be lost, or
dissipated in many devices.

Increasing the efficiency of a device depends on its
purpose

Most devices convert electric energy to mechanical
energy, where the worst “offender” of waste energy is
friction
 The easiest way to increase the efficiency is to decrease the
friction in these devices

For devices that produce heat energy, insulation is the way
to go
 Think about your oven
 Even the fridge – to prevent heat from getting in, you would
insulate the fridge better

C+R Pg. 342
 #1-8