Transcript Unit D Section 4.0 - Calgary Christian School

Unit D Section 3.0
Devices and systems convert energy with varying
efficiencies.
3.1 – Energy Forms and Transformations
• Energy is the ability to do work
• Common forms of Energy:
• Chemical Energy is the energy found in
chemicals, including food
• Glucose is a common molecule used for
the production of energy in humans
• Chemical energy in the form of glucose
can transformed to mechanical energy
for movement
Transformations
Thermocouples
• A Thermocouple is a device that can
convert Thermal energy to Electrical
energy
• Consists of two metals joined together
that conduct heat at slightly different
rates
• When the metals heated, this
difference in conduction results in
electricity flowing from one metal to
the other
• The temperature affects the amount of
electricity produced, so you can use a
thermocouple as a thermometer
• A thermocouple can be useful to
ensure surfaces, like steel or other
metals or metal alloys, are
appropriately heated for machining,
or to gauge when a container or
location is too warm and coolants
need to be introduced.
http://www.youtube.com/wat
ch?v=igxYxhD82lU
3.2 Energy Transformations involving
Electrical and Mechanical Energy
• Danish scientist, Hans Christian Oersted
conducted an experiment where he
deflected a (magnetic) compass needle
with a current carrying wire
• He found that there is a relationship
between electricity
and magnetism
• Faraday, constructed the first electric
motor
• He used electromagnetic forces to
move an object
• An Electromagnet is a coil of insulated
wire (usually wrapped around a soft
iron core) that
becomes a magnet
when current flows
through it
• How do you keep an electromagnet
spinning in a magnetic field? The trick is to
switch the direction that the current travels
through the coil just as it aligns with the
magnetic field of the permanent magnet.
Reversing the current reverses the polarity
(the north and south ends) of the
electromagnet. It will then continue
turning in order to align the opposite way.
Changing the polarity of the
electromagnet every half turn causes the
electromagnet to be continuously pushed
and pulled by the permanent magnet.
Electric Motors
3 Parts:
• Commutator: is a split ring that breaks
the flow of electricity for a moment
and then reverses the connection of
the coil
• Stationary Magnetic Field
• Armature: is the rotating shaft with coil
wrapped around it
Electric Motors
• Polarity: A potential difference
between two points of an electric
circuit describing which of the two
points has the higher electric potential
• Direct Current: current that flows in
only one direction
• Symbol: DC
• Devices that use it:
• most devices that consume electricity
-- cars, planes, light rail systems,
computers, consumer electronics, and
pretty much anything with a battery -actually run on DC
• Alternating Current: current that flows
back and forth 60 times per second
• Symbol: AC
• Devices that use it: electricity in your
household circuits
• http://www.bbc.co.uk/schools/g
csebitesize/science/add_aqa/el
ectricity/mainselecact.shtml
Transformers
• device that changes electricity at one
voltage into electricity at a different
voltage
• a step-up transformer
increases the voltage
• a stepdown transformer
decreases the voltage
Transformer
• http://www.youtube.com/watch?v=9
g9mrjosAZA&app=desktop
Generating Electricity
• Michael Faraday demonstrated that
electrical current could be generated
by moving a conducting wire through
a magnetic field
• This is called Electromagnetic
Induction
• This discovery provided a way to
generate a steady supply of large
amounts of energy (A Generator)
• http://www.youtube.com/watch?v=20
Vb6hlLQSg
• Energy 101: Electricity Generation
One simple way to think about a generator
is to imagine it acting like a pump pushing
water through a pipe. Only instead of
pushing water, a generator uses a magnet
to push electrons along. A water pump
moves a certain number of water molecules
and applies a certain amount of pressure to
them. In the same way, the magnet in a
generator pushes a certain number of
electrons along and
applies a certain amount
of "pressure" to the
electrons.
Topic 3.3 Measuring Energy
Input and output
• Power: is the rate at which a device
converts energy
• Watt: is the unit of power (W)
For an electrical device, the power is
the current multiplied by the voltage.
power (P), current (I), and voltage (V) is
• P = I × V (watts = amperes × volts).
Power calculations
Power rating
• The power rating of most small
appliances in your home is:
1500 Watts or less
• A stove might be 7000W
• A calculator could be only 0.4W
Energy consumption
• Energy consumption: the amount of
energy a device uses
• Recall that energy is measured in
J - joules (watts × seconds).
• The energy consumption of an
electrical device is its input power
multiplied by the time the device is
used: E = P × t.
Energy consumption calculations
Kilowatt hours
• Kilowatt hour: commonly used unit of
electrical energy, equal to a power
consumption of 1000 W for one hour
• Electricity meters measure the energy
used in kilowatt hours. The electric
company then bills you for every
kilowatt hour used. This cost can add
up—a Canadian family's energy bill
can be over $100 a month.
•
Calculating kWh
Law of conservation of energy
• Law of conservation of energy: is the
fundamental principle that energy
cannot be created or destroyed
• However, we usually find that the
output energy of a device or system is
smaller than the input energy,
sometimes much smaller.
• Most often, the missing energy is lost
or dissipated as heat.
Efficiency
• Efficiency: is the ratio of the useful
energy output to the total energy
input in a device or system; usually
given as a percent
Efficiency
Comparing Efficiencies
• fluorescent lights are about four times
more efficient than incandescent lights.
Although fluorescent tubes also produce
more heat than light, they transform about
20% of their input energy into light.
• Arc-discharge lamps are even more
efficient. they produce light by passing an
electric arc through a vapour of a metal
such as mercury or sodium. Most cities use
these high-efficiency lamps for streetlights.
3.4 Reducing the Energy Wasted by Devices
Why reduce energy consumption?
• Less electricity used = less money and
reduces environmental impact
Combustion Engine
Improving Efficiency
Increasing the efficiency of a device
depends on its purpose
• to decrease friction of moving parts as
much as possible, you can use improved
bearings and lubricants
• Adding more insulation around the
reduces the amount of heat escaping
through the walls of the oven or the sides
of the refrigerator