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Quantifying Energy

• Quantity is a number http://www.youtube.com/watch?v=vnwRH0uSxsk

• Joules the energy addict. How do we know she is an addict? *http://www.youtube.com/watch?v=6XFBH53TYuw

How do we assign a number to energy?*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 familiarA 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/watch?v=XKCZn5MLKvk

http://www.youtube.com/watch?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=AXeq0ZIEKNg

definition with a biological example• *http://www.youtube.com/watch?v=J4Vq-

xHqUo8&feature=related• http://www.youtube.com/watch?v=JRp_iSaVRjE• http://phet.colorado.edu/en/simulation/circuit-

construction-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 wireWire length

Longer wire equals greater resistanceWire thickness

Thick wires equal low resistanceMaterial wire is made of

Copper and aluminum have low resistance and are used to carry current over a long distanceTungsten has high resistance so it gets hot as electric current moves through it so it is used in light bulbs

Wire temperatureCooler 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 3Explain, 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.