Transcript Energy - District 273 Technology Services

1-2
Quantifying Energy
• Quantity is a number
• Joules the energy addict. How do we know
she is an addict?
*http://www.youtube.com/watch?v=6XFBH
53TYuw
How do we assign a number to energy?
http://www.youtube.com/watch?v=vnwRH0uSxsk
*http://www.youtube.com/watch?v=vnwRH0uSxsk What
from start to about 2:17
Joules the metric unit
• A joule (J) is the unit of
measure for energy
• used in the International
System of Units (SI) and
metric system
• It is named after English
physicist James Prescott
Joule, who developed the
theory of conservation of
energy
Joules the metric unit
• Joules = the amount of
energy an object of one
Newton (about ¼
pound) has when it’s
1meter (slightly more
than 3 feet) above the
ground
• http://www.youtube.com/
watch?v=zt9nEjagSYY
Infer
• 1 goose that is
1000m above is how
many joules?
• See joules on this
surge protector. How
heavy would an
object be 1 meter
above ground to
equal that many
joules?
Since J is not familiar
A joule is the amount of energy needed to
raise the temperature of one gram of cool,
dry air by one degree Celsius. A quiet
person produces 100 joules of heat energy
every second.
*http://www.youtube.com/w
atch?v=XKCZn5MLKvk
http://www.youtube.com/wa
tch?v=i5JHx9bIxBs
Since J is not familiar
• Convert J to calorie then to Calorie
• 4.2 joules = 1 calorie roughly
• A calorie is the amount of energy required
to warm 1 g of water 1 °C at a constant
pressure (1 atm).
https://www.youtube.com/watch?v=uz6201OJ1Qo&feature=youtube_gdata_player
http://www.youtube.com/watch?v=qZaj2hld0HM
•
1000 calories = 1 Calorie as we know
them of food labels
• How many joules
then equal a Calorie?
Since J is not familiar
• A watt, the SI unit of power; it is defined as
one joule per second
• A kilowatt-hour (kWh), often seen on
household electricity meters, is equal to
3,600,000 J.
http://www.youtube.com/
watch?v=OrMUIWcTeQ8
How then are C related to Kwh
• If one KWh is 3,600,000 joules and 1 Cal
is 4200 joules, then how are KWh and Cal
related roughly?
• How many Calories would you need in an
hour to get the same number of joules as
a KWh?
• Need more hints: 1 Kilowatt Hour = 860
420.65 calories per hour; that’s the small
calorie so now estimate the equivalence in
Calories.
Efficiency
• Which is more scientific definition?
(1)effective operation as measured by a
comparison of production with cost (as in
energy, time, and money)
(2)the ratio of the useful energy delivered
by a dynamic system to the energy
supplied to it
Efficiency
• So what does that mean? The ratio of the
useful energy delivered by a dynamic
system to the energy supplied to it.
• Quantify with formula.
Efficiency
• How can we find out if something like our
body is efficient?
Efficiency
• How can we display it on a graph?
• What goes on the x axis?
• What are you manipulating?
• What goes on the y axis?
• What is changing
because of the
manipulation?
(It’s important to
Obtain energy)
Graphing Efficiency
• What goes on the x axis? The
independent variable
• What are you manipulating? Your Calories
you put in and the Calories you use.
• What is changing because of the
manipulation? The percent efficiency
• What does that look like?
• Hint: 2 lines on 1 graph
• http://www.youtube.com/watch?v=ASO8izbYNYc&playnext=1&list=
PL345E020ED625F274&feature=results_video
Ohm’s Law
• Electrical circuits can be quantified using
Ohms law
Ohm’s Law
• We need to be able to describe it in words
• *http://www.youtube.com/watch?v=AXeq0ZIEKN
g definition with a biological example
• *http://www.youtube.com/watch?v=J4VqxHqUo8&feature=related
• http://www.youtube.com/watch?v=JRp_iSaVRjE
• http://phet.colorado.edu/en/simulation/circuitconstruction-kit-dc simulation that is quick and
fun to use on your own
Voltage Difference
• Symbol V in the formula
• Measuring unit is V for volts
• The potential difference in charge between
two points in an electrical field
Resistance
• Symbol R in the formula
• Measuring unit Ω for Ohms
Factors affecting resistance of a wire
Wire length
Longer wire equals greater resistance
Wire thickness
Thick wires equal low resistance
Material wire is made of
Copper and aluminum have low resistance and are
used to carry current over a long distance
Tungsten has high resistance so it gets hot as electric
current moves through it so it is used in light bulbs
Wire temperature
Cooler wire equals lower resistance
Current
• Symbol I in the formula
• Measuring unit A for Amps
• Current is the rate at which electric charge
flows past a point in a circuit. In other
words, current is the rate of flow of electric
charge.
Practice
• http://www.wisc-online.com/Objects/ViewObject.aspx?ID=dce11904
• Question 1:
For a given amount of water pressure, which will flow a
greater rate of water: a small (restrictive) nozzle or a
large (unrestrictive) nozzle? Explain how this relates to
the study of voltage, current, and resistance in a simple
electric circuit.
Practice
• Question 2:
Is this graph true?
Practice
• Question 3
Explain, step by step, how to calculate the
amount of current (I) that will go through
the resistor in this circuit:
• Question 4
What is the value of this resistor, in ohms
(Ω)? 1mA=.001A
Power can be quantified
• Formulas
• Definition: power is the rate
at which energy is
transferred, used, or
transformed.
• Measuring unit of power is the
watt (W)or joule per second
(J/s)
• What does E stand for and
what is it measured in? What
about t?
Practice
• Question 5
• If your air conditioner used 375 kWh in 125
hours, how many kW were used?
• Question 6
• If the electric company charges $0.13 per kWh,
how much did that air conditioner cost you?
• Question 7
• If you were billed for 80 kWh and you know that
your dryer only uses 4 kW, how many hours was
it in use?
Ohm’s Law and Power are
Related
OR
Practice
• Question 8:
• How will you find Energy if given volts,
current, and time?
• What will Energy be measured in?
Practice
• Question 9:
• Read the following description of the execution of
Kenneth Stewart in Virginia on 23 September 1998.
• The electric cycle, 1,825 volts at approximately 7.5 amps
for 30 seconds, then 240 volts at approximately 1.5
amps for 60 seconds … a 5 second pause intervenes,
and the cycle is repeated, was designed to render the
condemned brain dead within the first few moments. The
function of the remainder of the cycle is to stop the
body's organs so that a physician can certify that death
has occurred … (Source: Amnesty International).
• Determine …the total electric energy delivered to Mr.
Stewart on the day of his execution.
Practice
• Question 10
• Infer what may have happened on June 4th
to cause such an increase in electrical use
but not gas.
Energy Bills and Appliance
• With up to 2 other people you will analyze
the class packet that shows how to read
an energy bill and the power usage of
appliances. On 1 paper your group will do
the following tasks taking turn who writes.
Be sure your summary and questions are
clear.
• See your worksheet for details.