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ENERGY
In science, energy is defined as the ability to do
work.
5 common kinds of energy are:
mechanical (movement), chemical,
thermal (heat), electrical, and light
energy.
MECHANICAL ENERGY- DOTTED LINES SHOW
MOTION.
MECHANICAL ENERGY
Energy of movement.
Includes the energy an object has because of its
potential to move.
A pendulum is a visible example of mechanical energy,
THIS IS A PENDULUM
A PENDULUM…
Is a mass that is suspended from a point
so that it can move back and forth. The
mass is lifted to one side, and then the
stored mechanical energy changes into
moving mechanical energy when the
mass falls.
CHEMICAL ENERGY
The energy stored in chemicals.
This energy is released during chemical
reactions when the chemical bonds of the
compound break.
Batteries use chemical energy.
FOOD:
Stores chemical energy, which can then be
used by your body to produce
movement.
THERMAL ENERGY
The total kinetic energy of all the particles in a
substance.
Kinetic energy refers to how fast the particles are
moving.
Warm objects have more thermal energy than cool
objects because the particles are moving faster.
BECAUSE…
Thermal energy refers to the total
kinetic energy of a substance, 100
mL of water at 75 degrees Celsius
will have more thermal energy than
50 mL of water at 75 degrees
Celsius.
ELECTRICAL ENERGY
The energy from the flow of electrons
through a conductor.
The electricity produced is from the
continuous movement of the electrons.
Electrical energy is used in televisions,
computers, etc.
LIGHT ENERGY IS…
Energy that travels in the form of a light wave.
Most common source of light energy is the sun.
Light energy allows people to see.
ENERGY TRANSFER
Energy transfer occurs when one type of energy is
transferred or moved from one object to another.
For example, thermal energy is transferred from the
stove to a pan through conduction.
The type of energy does not change when
energy is transferred.
ENERGY TRANSFORMATION
Energy is transformed when it changes from one type of
energy to another.
When glucose (a simple sugar) is broken down in the
body, chemical energy is transformed (changed) into
mechanical energy for the movement of muscles and
for thermal (heat) energy to keep warm.
ENERGY TRANSFORMATION
When you turn on a light bulb, electrical energy is
transformed (changed) into thermal and light energy
as the electrons flow through the filament of the bulb
Energy can nether be created nor destroyed; it can only
be transformed (changed) from one form to another.
Law of conservation of energy.
ELECTRICAL STORAGE CELLS
A cell is a commonly used device that changes chemical
energy into electrical energy. This is made possible by
using 2 different metal electrodes and an electrolyte.
Within a cell, a chemical reaction occurs that releases
electrons that travel from one electrode to the other.
Different electrolytes and electrodes will produce cells
with different properties.
ELECTRICAL STORAGE CELLS
A cell’s strength can also be changed by varying the
concentration of the electrolyte used.
The intended purpose of the cell will determine what
kinds of electrolytes and electrodes should be used
and which type of cell would be best.
TWO KINDS OF CELLS: WET & DRY CELLS
Wet cells: have liquid electrolytes.
Dry cells: use a paste
Cells that cannot be recharged are called
primary cells and, and rechargeable cells are
called secondary cells.
BATTERIES
Two or more cells combined together
make a battery. A 12-volt car
battery has six cells connected in
series.
THIS IS A WET CELL
Lemon juice electrolyte (lemon) with a carbon electrode and zinc electrode.
THIS IS A WET CELL
A chemical reaction occurs, and the electrons move from the zinc
electrode (-) to the carbon electrode (+) through the electrolyte
(the lemon juice).
TRANSFORMING ELECTRICITY
Electricity is a form of energy that can be
changed from, or into, another form of
energy by technological devices.
TRANSFORMING ELECTRICITY
Technological
Device
Motor
Initial (starting) Final energy
energy form
form
Electrical
Mechanical
Generator
Mechanical
Electrical
Thermocouple
Heat
Electrical
ELECTRIC MOTOR
Is a device that transforms electrical energy into
mechanical energy. This is made possible by
the use of permanent magnets, an armature,
brushes, and a split ring commutator.
Because of the continual switching of the
polarity of the magnets, the armature spins.
GENERATORS
Have the same basic parts as a motor, but in the case of
a generator, mechanical energy is converted into
electrical energy.
Generators can produce direct current (DC) or alternating
(AC). The more common form of current is AC
Power companies generate AC.
GENERATORS
Power companies use high voltage (500 000 V)
transmission lines to get electricity from the
generating stations to your house.
The power lines going into your house are only 240 V. A
transformer is used to step up or step down voltage
depending on the need. Inside your house, voltage is
dropped (stepped down) again to 120 V for most
appliances.
ELECTRICAL SAFETY
Electrical current is measure in amperage.
Voltage is measure in volts.
If either number is high, the electrical current
can be dangerous.
DEVICES:
Are required to have labels stating the necessary voltage and max
amperage.
For example, an electric mitre saw plugs into a 120 V receptacle and
is rated at 15 A of current.
Know the voltage and amperage of electricity you work with
Respect high voltage transmission lines
Do not plug electrical devices into a wall if cords are frayed.
Avoid mixing water and electricity.
Be careful of shocks from wall outlets- can cause serious harm.
ELECTRIC CURRENT
Atoms build up a charge by losing or gaining electrons.
An atom that loses electrons becomes positively charged.
An atom that gains electrons becomes negatively charged.
The behaviour of charged objects can be predicted according to the
law of electrical charge.
LAW OF ELECTRICAL CHARGE
Objects with opposite charges attract each
other.
Objects with the same/like charge repel
each other.
STATIC ELECTRICITY
When 2 objects with the opposite electrical charges come close
enough to each other to allow electrons to move from the
negatively charged object to the positively charged one.
This movement is the cause of the shock a person felt or the zap
heard or a spark seen as the charged objects return to a neutral
condition.
A lightening flash is a very large discharge of
static electricity.
STATIC ELECTRICITY
Is unpredictable and occurs
randomly.
CURRENT ELECTRICITY
Is predictable (you can count on it being therelike when you plug a device into the wall).
Is the movement of electrons along a conducting
path. For example, current electricity moves
along copper wire.
CONDUCTORS, INSULATORS, AND RESISTORS
Conductors allow for the movement of electricity, whereas
insulators oppose the movement.
Resistors allow some, but not all, of the current to pass
through. Current passing through a resistor can produce
heat and light. Resistance is what makes a light bulb or a
stove element work. Common examples of conductors,
insulators, and resistors are listed as follows:
Conductor- copper and aluminum
Insulator- plastic and rubber
Resistor- tungsten filament and heater element.
CONDUCTING ELECTRICAL FLOW
A switch can be used to control the flow of electricity through
a circuit by turning it on and off.
When the switch is open, the conducting points are not in
contact with each other and no current can flow through.
When the switch is closed, the conducting points are
connected, and current can flow through the system. That
is why the light in a room will turn on when the light switch
is set to “on”.
RESISTANCE:
In an electrical circuit is a measure of how easily the current flows.
A resistor in a circuit is similar to a water pipe with a small diameter. Water
flowing in a narrow pipe has more resistance than water flowing in a
wide pipe.
Because the resistor makes it more difficult for current to flow through, the
voltage (or pressure) drips as it flows through the resistor.
Components such as bulbs and motors act as resistors in a circuit.
CURRENT, RESISTANCE, AND VOLTAGE
Current, resistance and voltage are directly related to
each other.
The voltage of a system depends directly upon the
current and resistance in a circuit.
Increased voltage/increased current.
A narrow path creates more resistance. If resistance is
high, not as much current can flow. As resistance
increases, current decreases.
ELECTRICAL TERMS
The relationship between current, voltage
and resistance in a circuit is describe by
Ohm’s Law using the terms listed in the
table on the following slide.
ELECTRICAL TERMS
Electrical Terms
Definition
Unit of
Measurement
Symbol
Current
Rate of flow
Ampere (A)
I
Voltage
Force (strength)
of flow
Volt (V)
V
Resistance
Obstacle to
flow
Ohm (Ω)
R
OHM’S LAW
The voltage of a system is directly related to the current
multiplied by the resistance:
V=IxR
V = Voltage
R = V/I
I = Current
I = V/R
EXAMPLE
An electric heater uses 12 A of electricity when it is
plugged into a 120 V outlet. What is the resistance of
the heater?
Solution:
R = V/I
= 120 V/12 A
= 10 Ω
CIRCUITS
An electrical circuit is made up of 4 main
parts/components (subsystems):
Source: Cell or battery
Conductor: Wire
Control: Switch
Load: Lamp or motor
CIRCUITS
When the switch is turned off and the current is
interrupted, the circuit is said to be open.
When the switch is on, allowing for the flow of
current, the switch is closed.
CIRCUITS
If a simple circuit consisting of a cell connected
to a switch and a light does not work,
troubleshooting can possibly determine the
cause. Troubleshooting involves checking to
see if the cell is dead, the light is burnt out, or
if the wires are improperly connected.
CIRCUITS
Can be set up as series circuits or as
parallel circuits.
CIRCUITS
MICROCIRCUIT
Microcircuits, sometimes called integrated circuits, are used in
televisions and computers. They are extremely small and use
less current and voltage than circuits which carry electricity
throughout a house. Microcircuits contain microscopic
transistors and resistors.
More than a million components can be placed on a chip that is no
larger than one square centimetre. A transistor is often used
instead of a switch in a microcircuit. Transistors have no moving
parts and can be made much smaller than traditional switches
used in homes.
INPUT, OUTPUT, AND EFFICIENCY
Input refers to the amount of energy put into a
device, and the output refers to the amount of
energy that comes out. A device may change
the type of energy, but not the amount. For
example, a light bulb’s input energy is in the
form of electrical energy, and its output energy
is in the form of light and heat energy.
EFFICIENCY:
Is the ratio of useful energy that comes out of a device
compared to the total energy that went into it.
Remember that energy cannot be destroyed, but it can
be converted or changed from one form to another.
% efficiency = output/input x 100%
EXAMPLE:
What is the efficiency of an incandescent light bulb (the kind in a
lamp) that releases 62 kJ of light energy from an input of 1,560
kJ of total energy:
Solution:
% efficiency = 62 kJ/1,560 kJ x 100
=4%
The incandescent light bulb is 4% efficient in producing light and
wastes 96% of the input energy in the form of heat. It is very
inefficient.
A fluorescent bulb (like the ones in our classroom) is more efficient
than an incandescent bulb.
POWER
Power is measured in watts, and is the rate at which a
device converts energy. Power is dependent on the
current rating of an appliance and the voltage passing
through it. Power is calculated using the following
equation:
P=IxV
Power (watts) = current rating (amps) x voltage (volts)
EXAMPLE:
What is the power rating in watts (W) of a curling iron
that plugs into a 120 V circuit and uses 9 A of
current?
Solution:
P=IxV
P = 9 A x 120 V
P = 1080 W
ENERGY
Energy (E) is dependent on power (P) and time (t).
Energy is calculated using the following equation:
E (joules) = P (watts) x t (seconds)
Challenge: How much energy is used by a 4 A appliance
that is plugged into a 120 V circuit for 4 minutes?
STEP 1
Calculate the power used:
P=IxV
= 4 A x 120 V
= 480 W
STEP 2
Calculate the energy used:
E=Pxt
= 480 W x 4 minutes x 60 seconds/minute
= 115 200 J
PRODUCING & DISTRIBUTING…
Electricity is expensive. Power companies pass their
costs on to the consumer and charge per kilowatt
hour of use.
Example: What is the cost of operating a 2 400 W
heater two hours per day for a 20-day period? The
charge per kilowatt hour is $0.10 (in other words, .10
cents)
STEP 1
Change watts to kilowatts
2 400 W/1000 = 2.4 kW
STEP 2
Multiply by the hours of use.
2.4 kW x 2 hours = 4.8 kWh (kilowatt hours)
STEP 3
Multiply by the days of use.
4.8 kWh x 20 = 96 kWh
STEP 4
Multiply by the cost per kilowatt hour
96 kWh x $0.10 = $9.60
ANALYZING ENERGY DEVICES:
Law of Conservation of energy states that energy can
neither be created nor destroyed; it can only be
transformed (changed). Sometimes a lot more energy
is put into a device that what is converted into useful
energy. The energy that has been lost is often lost in
the form of heat as a result of friction. All mechanical
devices will lose some useful energy because energy
dissipates (is spread) to the surroundings in the form
of heat.
NEW APPLIANCES:
Are often more energy efficient than they were in the past. They are better
designed and better insulated than previous models. Such appliances
carry the EnerGuide labels that indicate their energy consumption
ratings.
CONSERVING ENERGY AT HOME?
Turn off lights when leaving a room.
Use fluorescent bulbs instead of incandescent.
Wash dishes by hand instead of dishwasher.
Hang wet clothes on a line instead of using the dryer.
Turn off TV and computers when not being used.
Use air conditioners only when necessary.
Turn down heat at night or when people aren’t home.
Etc.
ENERGY SOURCES
Much of world’s electricity is generated from coal and
uranium. These sources are slowly being depleted
(used up). The search is on to find alternative,
sustainable sources of energy.
Winds, tides and steam (geothermal energy) are now
being harnessed to produce electricity. Scientists are
investigating how to produce electricity from solar
panels and fuel cells.
ELECTRICITY AND THE ENVIRONMENT
Fossil fuels, such as gas and coal, which are used to
generate electricity have an impact on the
environment.
Byproducts of coal-generated power cause pollution and
global warming.
Carbon dioxide, sulfur dioxide, and nitrogen oxide
emitted into the atmosphere cause the greenhouse
effect and produce acid rain.
ELECTRICAL TECHNOLOGIES
Cellphones, computers, MP3 players, dishwashers and
TVs are just some of the electrical technologies
people use every day. They have many benefits, but
there are also some costs associated with them.
To assess the environmental impact of a specific
technology, the impact of the manufacturing, daily
usage, and disposal of the technology need to be
considered.
EXAMPLE:
Manufacturing computers requires a lot of energy. Most of this
energy is produced by burning fossil fuels which adds to the
greenhouse effect (heating of the Earth) and climate change. It
also uses a lot of chemicals and materials (resources).
Computer technology also changes quickly and becomes outdated.
Outdated machines are thrown out and pile up in landfills.
New recycling facilities reduce the amount of electronic materials
that end up in landfills, but the recycling process also requires
energy from fossil fuels.
ENERGY CONSERVATION & SUSTAINABILITY
Fossil fuels are non-renewable. This means that people
need to conserve these resources to prevent them
from being used up too quickly. There are many
things to consider when deciding how to conserve
energy.
For example, an electric car does not burn gasoline, but
the electricity that it uses may have been generated
by burning fossil fuels.
ENERGY CONSERVATION & SUSTAINABILITY
When resources are replenished at the same rate they
are used, they are said to be sustainable.
This concept may include conserving the current nonrenewable resources so they are available for long
periods of time.
Some sustainable choices people are making include
biking, purchasing high efficiency appliances, and
turning lights off when they leave a room.