Sunday, November 07, 2004

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.

































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