Download Input Vs. Output

Input Vs. Output
Section 3.3 p. 332
Learning Outcome
• Apply appropriate units, measures and devices in determining and
describing quantities of energy transformed by an electrical device,
by:
• Measuring amperage and voltage, and calculating the number of
watts consumed by an electrical device, using the formula P = IV
[power (in watts) = current (in amps) × voltage (in volts)]
• Calculating the quantity of electric energy, in joules, transformed by
an electrical device, using the formula E = P × t [energy (in joules) =
power (in watts) × time (in seconds)]
Recall
• Law of Conservation of Energy states: That energy cannot be created
or destroyed, only transformed from one form to another
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An energy transformation consists of
Input Energy source
Converter (system that enables the change)
Output Energy
• Two Types
• Useful output (desired)
• Wasted output
Power
• Power is the rate at which a device converts energy
• The faster a device converts energy, the greater its power rating is
• Power is measured in Watts (W) = Joules/second (J/s)
• Power is represented by a mathematical relationship
•P=I x V
• P= Power (W) (J*s)
• I= Current (A)
• V= Voltage (V)
• Power is represented by the amount of current X voltage
• Think back to the waterfall models
• Which one will consist of the most powerful?
Calculating Power
• Understanding the power rating of an electronic device is using will help in
understanding the potential energy usage, and the output it will produce
• Think of lightbulbs, most lightbulbs will have a power rating directly on the bulb (i.e. 60W)
• This is important since it needs to coincide with the rating of the device, or safety issues could arise. (if
the bulb is drawing more power than the device can handle safely, than the excess heat can create a
safety hazard)
• P=IxV
• I= P/V
• V=P/I
• A hair dryer has a power rating of 1000W. It is plugged into a 120-V outlet. What
is the current flowing through the hair dryer?
• 8.33A
Energy
• Since Power is the rate at which energy is converted. Knowing a devices power
rating will allow us to calculate the amount of energy being used by a device
• Energy is calculated by using the mathematical relationship
• E=P x t
• E=Energy (J) W*s
• P= Watts (W) (J*s)
• T= Seconds (s)
• A microwave oven has a power rating of 800W. If you cook a roast in this oven
for 30 minutes on high, how many joules of electrical energy are converted into
heat by the microwave?
• 1,440,000 J or 1.4 MJ
Kilowatt Hours
• Think of anything that has the prefix Kilo in
it.
• What is the one common thing about it?
• 1000 of what ever the unit of measurement is
• When we measure energy we use J
(Watts/second).
• This works well for small devices over short
periods of time.
• Not always practical in everyday society
• Power companies will use a measurement
known as kilowatt hours
• Watts are now measured by the kilowatts (1000
watts)
• Time is now measured in hours instead of seconds
(h)
• Go back to the previous example of the
microwave
• Watts = 800 (W)
=0.8 kW’s
• Time = 30 minutes (1800s) Now
• Therefore = 0.4 kW*h
Now
=0.5 h
Energy Dissipation
• Remember that no energy transformation is ever 100% efficient
• Input ≠ Useful Output
• All machines will require more input energy in order to achieve the desired amount of
Useful output energy
• This is due to the fact that most wasted energy will be dissipated as heat
• Friction between moving parts
• Inefficiency of design (hot plate, heats substance on the hot plate surface, but also heats the
area around that object)
Energy Efficiency
• The Efficiency of a device is a ratio involving the Useful energy that comes out of
a device, to the total input energy that went in.
• Calculated as a percentage (100)
• More Useable energy produced, the more efficient the machine will be.
• % Efficiency = Joules of useful ouput X 100%
Joules of Input Energy
• An incandescent light bulb used a 100 J of electric energy. It produced 5J worth
of Light energy and 95 J worth of heat energy. What is its Efficiency?
• 5%