Thursday, November 25, 2004

Lesson 20

ELECTRICITY LESSON 20 – Measuring Electrical Energy
Lesson: 20.
Take up Hwk: Measuring Electrical Energy Worksheet, other worksheet (series and parallel resistance), Handout, take up cp p.g 80-81
Overhead Watts and Joues – Measuring Electrical Energy
SW/HW: p. 83, 84, 85 (group work post answers on the board to discuss)
Hwk: Try CP pg. 86


Power - follow this link (there are pretty lights and fun cartoons!) http://www.saskschools.ca/curr_content/science9/electricity/lesson05t.html

Electrical energy - follow this link (it's got a much better description than I gave in class)
http://www.need.org/needpdf/infobook_activities/SecInfo/Elec3S.pdf
scroll down the page until you get to the part on electric power and electric energy and how the two are related...
Don't worry if you did not finish all of the assigned course pack information. We will do some of it in class tomorrow!

Wednesday, November 24, 2004

Lesson 19

ELECTRICITY LESSON 19 – OHM’s Law
Lesson: 19.
Take up Hwk: Pg. 319 #1-7, collect labs pg. 75-77, take up pg. 78-79
Quiz
Measuring Electrical Energy Worksheet/Handout
More resistance questions handout
Hwk: Complete Worksheets and course pack lab pg. 80, and pg. 81.


Resistance

1. Resistance is the property of a component which restricts the flow of electric current.

2. Energy is used up as the voltage across the component drives the current through it and this energy appears as heat in the component.
3. Resistance is measured in ohms, the symbol for ohm is an omega . 1 is quite small for electronics so resistances are often given in k and M. 1 k = 1000 1 M = 1000000 .
4. Resistors used in electronics can have resistances as low as 0.1 or as high as 10 M.

Resistors connected in Series

When resistors are connected in series their combined resistance is equal to the individual resistances added together. For example if resistors R1 and R2 are connected in series their combined resistance, R, is given by:

Combined resistance in series: R = R1 + R2

This can be extended for more resistors: R = R1 + R2 + R3 + R4 + ...

Note that the combined resistance in series will always be greater than any of the individual resistances.

Resistors connected in Parallel

When resistors are connected in parallel their combined resistance is less than any of the individual resistances. There is a special equation for the combined resistance of two resistors R1 and R2:

1 = 1 + 1 + 1
__ __ __ __
Rt R1 R2 R3 ...


Monday, November 22, 2004

Lesson 18

OHM's Law

Here's an opportunity to get you doing a little self teaching using the net:

Here is a couple of websites to help you on your way.

The first website teaches you how to perform calculations and gives you a definition of OHM's law:
http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html

This next site gives you a number of practice questions to get you comfortable with calculating resistance:
http://www.the12volt.com/ohm/page2.asp (make sure that you click the = sign if you want to check your answer)
Hwk:
QUIZ IS POSPONED UNTIL TUESDAY

ANNUAL LEARNING PLANS TO BE COLLECTED ON TUESDAY
VOLTAGE QUESTIONS TO BE HANDED IN TOMORROW CP PG 72 – 74
TODAY’S WORK:
- READ PG 316-319
- COPY DOWN EXAMPLE “SAMPLE PROBLEM” PG. 318
- IN PARTNERS ANSWER QUESTIONS 1-7 – HAND IN FOR COMPLETION
- FINISH ANY UNFINISHED LAB WORK TO BE HANDED IN TOMORROW.
- IF FINISHED EARLY COMPLETE LAB PG 80 IN COURSE PACK.
- STUDY FOR TOMORROW’S QUIZ

Saturday, November 20, 2004

Review For Quiz 3

QUIZ 3 REVIEW for Monday...

Cells - Series Cells vs. parallel Cells:

What is the difference in voltage between series cells and parallel cells
What is the difference in current between series and parallel cells?
How would you arrange to connect cells in a combination of series and parallel? What is the advantage of this?
Circuits - Series and Parallel
How do you connect a circuit in series? How do you connect a cirucuit in parallel?
Describe the movement of electrons through a series circuit and a parallel circuit.
What does Ohm's mean?
Describe how resistance affects the voltage across series and parallel circuits.
Describe how resistance affects the current across series and parallel circuits.
Study circuit diagrams from the assigned course pack questions. Try to calculate the voltage and current across the circuits.

What is the standard unit for measuring current and what is the SI for measuring voltage?


Read the following websites to help you along:
http://www.sirinet.net/~jgjohnso/electric.html
http://sol.sci.uop.edu/~jfalward/seriesparallelcircuits/seriesparallelcircuits.html
http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/seriesparallelcircuits.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/class/phscilab/electric.html
http://www.doctronics.co.uk/resistor.htm#what
http://www.doctronics.co.uk/resistor.htm#series_parallel - This is a really good one!


Thursday, November 18, 2004

Lesson 16, 17

ELECTRICITY LESSON 16 – Current
Lesson: 16.
Take up Hwk: Hand back quiz
Text pg. 314 Current, c.p. pg. 69
Lesson: Current
Current Overhead
Current Worksheet: Here
Lab investigation: build a simple series circuit and a simple parallel circuit
Homework: Complete worksheet and pg. 315 text #1-4

Overhead of Current Lesson:

Electricity is a term used to describe the energy produced (usually to perform work) when electrons are caused to directional (not randomly) flow from atom to atom. In fact, the day-to-day products that we all benefit from, rely on the movement of electrons. This movement of electrons between atoms is called electrical current.


Electricity current is the rate at which electricity flows through a circuit, to transfer energy. Current is measured in Amperes ("A"), commonly called Amps. Analogy: Flow rate in a water pipe.


It was not until 1600 that a man named Dr. William Gilbert coined the term “electrica,” a Latin word which describes the static that occurs when amber and other materials are rubbed.

THE LAW OF CONSERVATION OF CHARGE
1. THE LAW OF CONSERVATION OF CHARGE STATES THAT AN ELECTRIC CHARGE CANNOT BE CREATED OR DESTROYED.





DC CURRENT
As long as electrons are flowing through the atoms of the circuit, work is being done. We can see that work is being done in this circuit because it lights the light bulb. The actual amount of electrons that are flowing is determined by the type and size of the battery as well as by the size and type of the light bulb. We could reverse the polarity of the battery by switching the contacts (wires), and the current would flow in the opposite direction and the bulb would still light.Either way the battery is connected to the circuit, current can only flow in one direction. Direct current (DC) can also be generated by means other than batteries. Solar cells, fuel cells, and even some types of generators can provide DC current.


AC CURRENT
AC is short for alternating current. This means that the direction of current flowing in a circuit is constantly being reversed back and forth. This is done with any type of AC current/voltage source.
The electrical current in your house is alternating current. This comes from power plants that are operated by the electric company. Those big wires you see stretching across the countryside are carrying AC current from the power plants to the loads, which are in our homes and businesses. The direction of current is switching back and forth 60 times each second.


ELECTRIC CURRENT WORKSHEET

P.314-315
1. What is electric current? What type of charge moves through a circuit?
2. What do the protons do in an electric current?
3. Electric current is a measure of what? What are the units for electric current?
4. Current is measured with what instrument connected to the circuit in series?
5. What is the difference between static and current electricity?
6. The larger the current, what happens to the muscles in the human body?
7. What happens to muscle cells when electric current flows through them?
8. When does muscle contraction cease in a person?
9. What current is needed to feel a tingling sensation?
10. What is the value for the “let-go” threshold? What happens at the “let-go” threshold? Explain.
11. What happens if the current going through a person’s chest is 0.050 A or more?
12. How do you stop ventricular fibrillation?
13. What type of currents are needed to cause severe burns?
14. Before helping a victim of electric shock, what are some precautions that you need to do?


ELECTRICITY LESSON 17 – Measuring Voltage Lab
Lesson: 17.
Take up Hwk: Complete worksheet and pg. 315 text #1-4
Lab c.p. pg. 72 -74 (hand in questions – 2 marks per question)
Hwk: Complete lab at home to be completed no later than tomorrow must also include the worksheet calculations


Monday, November 15, 2004

Lesson 15 - Announcement

UNFORTUNATELY, THERE WILL BE NO MORE COMMENTS ALLOWED ON THIS WEB BLOG. SOMEONE HAS UNLAWFULLY GAINED ACCESS TO MY WEBSITES (BOTH GR. 9 AND 10) AND HAS BEEN POSTING INAPPROPRIATE COMMENTS. IT IS MY PREROGATIVE TO DISCONTINUE WEB COMMUNICATION IN ORDER TO MAINTAIN THE PROFESSIONAL, AND ACADEMIC INTEGRITY OF THIS SITE. I APPOLOGISE FOR ALL THOSE WHO ENJOY THE TUTORIAL COMPONENTS OF THESE SITES.

Here is the latest lesson:
ELECTRICITY LESSON 15 – Cells in Series and Parallel
Lesson: 15.
Take up Hwk: Discussion Questions text 311 #1-3
Hand back quiz
Lesson: Let’s get ready for OHM’s
Handout: Electrical Resistance and Ohm’s Law
Series Circuit and Parallel Circuit overhead
Lab investigation: build a simple series circuit and a simple parallel circuit
Homework: review concepts and make notes of the overhead IN YOUR OWN WORDS!
There will be a NOTEBOOK CHECK THIS WEEK!!! The following website has a copy of the rubric that will be used to assess your notebook: http://teachers.teach-nology.com/cgi-bin/notebook.cgi

Overhead Note Series and Parallel Circuits:
RECALL:
Amperage is a term used to describe the number of electrons moving past a fixed point in a conductor in one second.
Current is measured in units called amperes or amps
An ammeter is this instrument and it is used to indicate how many amps of current are flowing in an electrical circuit.

EMF is electromotive force. or VOLTAGE causes the electrons to move in a particular direction.
EMF is measured in units called volts.
A Voltmeter is this instrument and it is used to indicate how many volts of current are flowing in an electrical circuit.



Another way of saying this is: without EMF, there will be no current. Also, we could say that the free electrons of the atoms move in random directions unless they are pushed or pulled in one direction by an outside force, which we call electromotive force, or EMF.


SERIES / PARALLEL CIRCUITS

A series circuit is when there is only one path for the electrons to take between any two points in the circuit. In other words, the components, which are the battery, the switch, the ammeter, and light, are all in “series” with each other.


Like the series circuit, parallel circuits also contain a voltage (current) source as well as wires and other components. The main difference between a series circuit and a parallel circuit is in the way the components are connected. In a parallel circuit the electricity has several paths that it can travel


Build your own circuit using the net at:
http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/seriesparallelcircuits.htm

Check the sidebar to build both series, parallel, and series/parallel circuits!

Sunday, November 14, 2004

Lesson 14

ELECTRICITY LESSON 14 – Cells in Series and Parallel
Lesson: 14.
Take up Hwk: Discussion Questions text 307 #1-4
Quiz
Lesson: series and parallel circuits text pg. 310-311
Lab activity: build series and parallel circuits
Homework: pg. 311- 1-3



Board Note:

Cells and batteries may be connected in series, parallel, or combinations of both. Cells or batteries connected in series have the positive terminal of one cell or battery connected to the negative terminal of another cell or battery. This has the effect of increasing the overall voltage but the overall capacity remains the same. For example, the 12-V lead-acid automobile battery contains 6 cells connected in series with each cell having a potential difference of about 2 V. Another example of cells or batteries connected in series is shown in Figure 2. Cells or batteries connected in parallel have their like terminals connected together. The overall voltage remains the same but the capacity is increased. For example, if two 12-V automotive batteries were connected in parallel, the overall voltage for the batteries would still be 12 V. However, the connected batteries would have twice the capacity of a single 12-V battery. Another example of cells or batteries connected in parallel is shown in Figure 3.


Series and Parallel Cells Overhead

Portable equipment with high-energy needs is powered with battery packs in which two or more cell are connected in series. Figure 1 shows a battery pack with four 1.2-volt cells in series. The nominal voltage of the battery string is 4.8V.
Figure 1: Serial connection of four cells. Adding cells in a string increases the voltage but the current remains the same.



Parallel connectionTo obtain higher ampere-hour (Ah) ratings, two or more cells are connected in parallel. The alternative to parallel connection is using a larger cell. This option is not always available because of limited cell selection. In addition, bulky cell sizes do not lend themselves to build specialty battery shapes. Most chemistries allows parallel connection and lithium-ion is one of the best suited. Figure 3 illustrates four cells connected in parallel. The voltage of the pack remains at 1.2V but the current handling and runtime are increased four fold
Figure 3: Parallel connection of four cells. With parallel cells, the voltage stays the same but the current handling and runtime increases.



Here is a very good website for learning more on this topic:
http://www.batteryuniversity.com/partone-24.htm































Lesson 12, 13

ELECTRICITY LESSON 12, 13 – The Voltaic Cell
Lesson: 12, 13.
Take up Hwk: Discussion Questions text 303 #1,2,3,5
Lesson: Voltaic Cell
Overhead of Voltaic cell and note
Demo: of wet cell
Homework: pg. 307 #1-3,4

THE WET CELL



A Voltaic cell is a simple device with which chemical energy is converted into electrical energy. Two dissimilar metals (e.g., copper and zinc) are immersed in an electrolyte (e.g., a dissolved sulfate). If the metals are connected by an external circuit, one metal is reduced (i.e., gains electrons) while the other metal is oxidized (i.e., loses electrons). In the example above, copper is reduced and zinc is oxidized. The difference in the oxidation potentials of the two metals provides the electric power of the cell. The voltaic cell is sometimes also called the galvanic cell. The names refer to the 18th-century Italian scientists Alessandro Volta and Luigi Galvani.




The Dry Cell
The most common type of battery used today is the "dry cell" battery. There are many different types of batteries ranging from the relatively large "flashlight" batteries to the minaturized versions used for wristwatches or calculators. Although they vary widely in composition and form, they all work on the sample principle. A "dry-cell" battery is essentially comprised of a metal electrode or graphite rod (elemental carbon) surrounded by a moist electrolyte paste enclosed in a metal cylinder as shown below.






Discarding batteries poses a clear environmental danger. Batteries contain heavy metals, such as silver, nickel, cadmium, lead, mercury, lithium, manganese, and zinc, which can accumulate and concentrate in waterlife, wildlife, and humans. An example of the danger posed by batteries is that one mercury battery contained in six tons of garbage exceeds the allowable limit for mercury in solid waste as established by the federal government.




Lesson 11

ELECTRICITY LESSON 11 – Electric Potential (Voltage)
Lesson: 11.
Homework take up electric circuit pg. 66, 67
Take up Quiz
Text pg. 302, 303
Overhead Electric Potential voltage
Board note of electrical potential
Shared Reading – Electrical potential pg. 302.303.
Homework: Questions 1,2,3,5 pg. 303.


Electric circuit
If you take a continuous source of electricity, such as a battery, and connect conducting wires from the positive and negative poles of the battery to an electrical device such as a light bulb, you have formed an electric circuit.
Figure 1 - Electricity goes around in a circuit
In other words, the electricity flows in a loop from one end of the battery (or source of electricity) to the other end in a circuit. The concept of electric circuits is the basis for our use of electricity.
Take a battery for example. When the electrons build up on one side (negative end) and the protons build up on the other (positive end). You get a lot of potential energy. The electrons want to leave. The way to get them to leave is to connect the negative end to a good conductor and complete the circuit by connecting the conductor to the positive end of the battery. The attraction is very strong by the protons which causes the electrons to flow out of the battery, along the wire and then back to the battery.
As the electrons get “used up” and the protons become combined with the electrons at the “positive end” you get less electric potential or voltage. That’s when your stereo starts to fade and the voices get slow and the music doesn’t play as loud. Not enough electrons!!!




Here is a great site on Voltage:
http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/voltage.htm

Sunday, November 07, 2004

Electricity Lesson 10

ELECTRICITY LESSON 10 – Current Electricity “the electric circuit”
Lesson: 10.
1. Homework check in notebook. 2 marks
2. Quiz
3. Text pg. 300-301
4. Video – Tape 1 fourth episode
5. Overhead note the electric circuit and read pg. 300, 301 shared reading.
6. Make note of #1,2,3,4 and Electric Circuit Diagrams and symbols.
7. Course Pack activity “the electric circuit”
8. Homework: Finish c.p. pg. 66,67
Overhead:

Identify the following using pg. 300- 301 in your text:
A. Source of Electrical Energy B. Electrical Load
C. Electric Circuit Control Device D. Connectors

The worksheet from class is at this website:
http://www.morrowgalpern.ca/snc1d/snc1d_wiac.doc

Enjoy!!

Here is a website that explains everything to do with electric circuits:
http://www.infoplease.com/ce6/sci/A0816977.html

Lesson 9 Vander Graph Fun!!!

ELECTRICITY LESSON 9 – Vander Graph Fun
Lesson: 10.
Take up Hwk: pg. 62, 63 C.P.
Hand back Quiz
Vander Graph Fun – Electricity pamphlet “Ben’s demos”
4. Homework: List 5 potential hazards from using the Vander Graph, List 5 solutions to those hazards. Explain which demo you enjoyed the most and why.




Answers to Questions on Pg. 62, 63

1) Televisions have excess electrons traveling through the screen causing dust particles to go on the screen even after cleaning

2) Socks get charged by walking across carpets and attract dirt and dust with it’s excess electrons

Good Conductors: Fair Conductors: Good Insulators:
Silver Carbon Oil
Copper Nichrome Fur
Gold Human Body Silk
Aluminum Moist Human Skin Wool
Magnesium Acid Solutions Rubber
Nickel Earth Plastic

3) Electrical Cords and plugs are coated with plastic to insulate the excess electrons from jumping onto your body creating a “shock”

Pg. 63

1) The charged rod comes in contact with water molecules redistributing the electrons
2) The electrons are dispersed in the summer due to the humidity whereas winter has very little moisture in the air causing electrical build ups to occur.

Electricity Lesson 8

ELECTRICITY LESSON 8 – Insulators and Conductors
Lesson: 8.
Take up Hwk: pg. 65 course pack
Hand back Quiz
C.P. pg. 62, 63
Text pg. 280-281

Homework: Electricity package cross word and handout



Board Note:

A neutrally charged insulator and its response to a charged object being brought near it. In an insulator (such as plastic, rubber, glass, etc) the electrons are not free to move around the entire object. They are generally restricted to moving only around the atom they are attached to. They can move from one side of the atom to the other but are unable to leave the atom. As a result, we say that charges stay where you put them on an insulator.


In a neutrally charged conductor (usually metal) many of the electrons are free to to move around within the conductor. Conductors are often referred to as having a "sea of electrons" since the movement of the electrons looks like a flowing sea.

Draw a diagram to illustrate these concepts!




Electricity Lesson 7

ELECTRICITY LESSON 7 - Lightning
Lesson: 7.
Take up Hwk: Lab page 59 course pack – question pg. 61
Hand back Quiz
Lightening Video and questions teachers cupboard rm 336 C.P. pg. 65 Text pg. 290-291
Overhead of lightening (intro)
Homework: Complete pg. 65 course pack

Lightning

The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels at 186,000 miles in a second, almost a million times the speed of sound. Sound travels at the slower speed of one-fifth of a mile in the same time. So the flash of lightning is seen before thunder is heard. By counting the seconds between the flash and the thunder and dividing by 5, you can estimate your distance from the strike (in miles). But why does lightning cause thunder at the same time it strikes?

Lightning causes thunder because a strike of lightning is incredibly hot. A typical bolt of lightning can immediately heat the air to between 15,000 to 60,000 degrees Fahrenheit. That's hotter than the surface of the sun!
A lightning strike can heat the air in a fraction of a second. When air is heated that quickly, it expands violently and then contracts, like an explosion that happens in the blink of an eye. It's that explosion of air that creates sound waves, which we hear and call thunder.
When lightning strikes very close by, we hear the thunder as a loud and short bang. We hear thunder from far away as a long, low rumble.
Lightning always produces thunder. When you see lightning but don't hear any thunder, the lightning is too far away from you for the sound waves to reach you.
Light and sound will always move at different speeds. And lightning will always produce thunder because of a strike's high temperature. So no matter what, you will always see a flash of lightning before you hear thunder.

Here's some more good information on lightning:
http://www.nasaexplores.com/show_912_teacher_st.php?id=030108154146

Electricity lesson 5 and 6

ELECTRICITY LESSON 5 - Charging by Induction
Lesson: 5.
Take up Hwk: Discussion Questions c.p. 57, hand in friction lab
Lesson: charging by induction text pg. 184-185
Overhead (video) Halloween activity – Movie – electricity and Halloween?
Hwk: C.P. pg. 64

Note:
Charging by Induction
- charging an object without actually touching it -

A charged object will induce a charge on a nearby conductor. In this example, a negatively charged rod pushes some of the negatively charged electrons to the far side of a nearby copper sphere because like charges repel each other. The positive charges that remain on the near side of the sphere are attracted to the rod. If the sphere is grounded so that the electrons can escape altogether, the charge on the sphere will remain if the rod is removed.

The following website is a good resource for more information on charging by induction:

http://www.studyphysics.ca/30/charging.pdf


ELECTRICITY LESSON 6 - Charging by Induction
Lesson: 6.
Take up Hwk: Take up Charging by Contact Lab pg. 57 questions on the board
Quiz
Review concept of charging by induction (overhead)
Complete Lab C.P. pg. 59 –
Homework: answer question with diagram pg. 61


Answers to pg. 57 C.P.:

an object is neutral because there is an equal distribution of protons and electrons
a. electrons should be shown to jump onto the ebonite rod to give it a negative charge. The pithball should be shown to be attracted to the ebonite rod so that the neutral pith attracts to the negative ebonite rod where the electrons repel the pith electrons away but attract the protons
b. Acetate should be shown to have electrons jumping off of it to the paper towel. The pith should have been attracted to the rod in this case because the pith has more electrons than the rod.
a. On to the pith ball
b. out of the pith ball onto the acetate rod
4. a. negatively charged
b. positively charged (or some of the electrons leave the object and therefore make the object less negative)
5. Refer to page 58 in course pack.


Electricity - Lesson 3 and 4

ELECTRICITY LESSON 3 – The kinds of Electric Charges Lab
Lesson: 3.
Take up Hwk: Text pg. 275 #1-3
Lab – kinds of electric charges c.p. pg. 54-55
Hwk: Hand in lab completed by Friday, Oct. 29
hand out rubric


Assessment Rubric 3: Inquiry Investigation

CRITERIA
LEVEL 1
LEVEL 2
LEVEL 3
LEVEL 4

Initiating
· Asks few questions about the task
· Asks simple questions that may clarify the task
· Asks questions that clarify the task
· Approaches the task independently


· Demonstrates limited understanding of concept(s) related to the task
· Demonstrates some understanding of concept(s) related to the task
· Demonstrates sufficient understanding of concept(s) related to the task
· Demonstrates a solid understanding of concept(s) related to the task


· Has difficulty generating a hypothesis
· Generates a questionable hypothesis
· Generates a valid hypothesis
· Generates an insightful hypothesis

Performing and Recording
· Follows prescribed procedures with limited competence
· Follows prescribed procedures with moderate competence
· Competently follows prescribed procedures
· Selects and follows appropriate procedures

· Requires constant reminders to follow safety procedures
· Requires some reminders to follow safety procedures
· Follows required safety procedures
· Routinely follows all safety procedures

· Uses tools, equipment, and materials with limited competence
· Uses tools, equipment, and materials with some competence
· Uses tools, equipment, and materials competently
· Uses tools, equipment, and materials with a high degree of competence

· Makes few observations
· Makes observations but they may be insufficient to generate data
· Makes sufficient observations to generate data
· Makes rich observations

· Records little data
· Records data but organization is lacking
· Records relevant data in an organized way
· Records relevant data in an organized and skillful way

Analyzing and Interpreting
· Provides limited analysis of the data
· Provides some analysis of the data
· Provides sufficient analysis of the data
· Provides rich analysis of the data


ELECTRICITY LESSON 4 – Lab – Charging By Contact
Lesson: 4.
Take up Hwk: Lab – Kinds of electric Charges c.p. pg. 54-55
Lesson: Charging by Contact pg. 278 text
Lab: Charging by Contact C.P. 56, 57 (materials, pithball, fur, wool, clear acetate rod, black ebonite rod, pith ball electroscope)
Hwk: Discussion Questions c.p. 57

Note:
Charging by Contact

An electroscope is a device used to detect the presence of charge and it's relative amount. One method of charging the electroscope is by conduction or contact. This means that a charged object must actually touch the electroscope and transfer charge too. If the electroscope returns to normal after being touched by the charged object then it is quite possible that the charged object is so weakly charged that it is not willing to share its excess charge with the electroscope.

When charging something by contact it is important to note the following properties:

The objects must actually touch and transfer some electrons.
The objects become charged alike.
The original charged object becomes less charged because it actually lost some charge. Therefore, there is a limit to how many times it could be used to charge something without being recharged.


The following website is a fantastic resource on learning how charging by contact works!
http://www.sciences.univ-nantes.fr/physique/perso/maussion/statelec/PagesEngl/05Conta.html

Electricity Lesson 2

ELECTRICITY LESSON 2 – Charging by Friction Lesson

Lesson: 2.
Take up Hwk: C.P. pg. 52, 53
Overhead note.
Balloon Demo for friction
Hwk: Text pg. 275 #1-3.


Homework:
table pg. 273
Charging by friction involves two neutral, opposite, electrostatic series, at the top, positive, at the bottom, negatively, at the bottom of the chart, electrons, negatively
Positive (glass, wool, cat’s fur, human hair, calcium, magnesium, lead, silk, aluminum, zinc
Negative (cotton, paraffin wax, ebonite, polyethelene (plastic), carbon, copper, nickel, rubber, sulfur, platinum, gold)

Pg. 53 c.p.
electric charges remain static
driving a car touching the door get a shock
like repel, opposites attract
balloons rub together will repel, balloon rub touch to neutral wall
Repulsion – negative charges, attraction one object is either neutral or positive pg. 273 diagram
Bohr-rutherford diagram
becomes positive – becomes a positive ion
silk blouse negative charge higher on electrostatic chart

NOTES:

ELECTRICITY CHARGING BY FRICTION OVERHEAD
Charging by Friction

The only reason that we are able to use electricity in our modern world is that it is possible to separate positive and negative charges from each other.

• One way to do this is by rubbing two different materials together, known as charging by friction.
• Since the two objects are made of different materials, their atoms will hold onto their electrons with different strengths.

• As they pass over each other the electrons with weaker bonds to their nucleus will be “ripped” off of that material and collect on the other material.

Example 1: Rub a piece of ebonite (very hard, black rubber) across a piece of animal fur.
• The fur does not hold on to its electrons as strongly as the ebonite.
• At least some of the electrons will be ripped off of the fur and stay on the ebonite.
• Now the fur has a slightly positive charge (it lost some electrons) and the ebonite is slightly negative (it gained some electrons).
• The net charge is still zero between the two… remember the conservation of charge.



Electrostatic Series:

Electrostatic Series
Human Hands (if very dry)
Leather
Rabbit Fur
Glass
Human Hair
Nylon
Wool
Fur
Lead
Silk
Aluminum
Paper
Cotton
Steel (neutral)
Wood
Amber
Hard Rubber
Nickel, Copper
Brass, Silver
Gold, Platinum
Polyester
Styrene (Styrofoam)
Saran Wrap
Polyurethane
Polyethylene (scotch tape)
Polypropylene Vinyl (PVC)
Silicon
Teflon

MORE POSITIVE

MORE NEGATIVE
If we did a study of many materials and put them in order from those with the least desire for electrons to those with a very strong desire for electrons we would have created a Triboelectric series.
If two items from the list are rubbed together, then the item that is higher on the list will end up more positive and the lower one will end up more negatively charged. For example, if leather were rubbed with wool, the leather becomes positive and the wool negative. Yet if rubber is rubbed with wool, the rubber becomes negative and the wool positive.
It is important to note that this series is true only if the samples are clean and dry. The presence of moisture, dirt, or oils may cause some of the items to interact differently.