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# Electrostatics

PowerPoint: Chap 32 Electrostatics Hewitt

# Nikola Tesla ## Video: History Channel Modern Marvels Mad Electricity – Nikola Tesla

Could Tesla’s long-distance, wireless power transmission system have really worked? Many people believe this, and there have been an incredible number of conspiracy theories concerning this topic. However, Tesla’s work in this area was publicly demonstrated and well documented. Also, since his time thousands of scientists and engineers have also investigated how radio waves transmit electrical power. We can read about the results here: Tesla and wireless power transmission. ## 32.1 Electrical forces and charges

### Caution: the atom isn’t really like a solar system at all. Saying so is just a sometimes-useful-analogy. ### Solar system model of the atom: ## Conservation of charge

### In the section on Modern physics we will discover, however, that under amazingly extreme circumstance – such as inside a star – atoms can change the number of protons, through nuclear fusion.

Electrically charged objects ## Coulomb’s law

### How strong is this Force? Depends on r (their separation) http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/don_bahls/coulombs_law.html http://www.aplusphysics.com/courses/honors/estat/Coulomb.html

### (How do we find this number? That’s another story! For now, we’ll just give it to you ) ### (Or, as the distance increases, the force drastically drops?) ### it sets the strength of how strongly charged objects attract/repel. ### If k increases by an order of ten, we get the gray curve.

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### We can imagine electrical current looking like this: Red circles are metal atoms – including the nucleus, and almost all of the electrons. Smaller moving circles are valence electrons that are not tightly bound to any one atom. ## e = 1.602 x 10 -19  C

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## Conductors and Insulators

Electrons are more easily moved in some materials than in others. ### Notice that when no charged object is near the conductor, the electrons evenly distribute themselves within the conductor.

Text above adapted from: Science Joy Wagon, 1998 ### (There would also be an attraction if the object was positively charged.) As a result, we say that a neutral insulator will always be attracted to a charged object.

Text above adapted from: Science Joy Wagon, 1998

## The speed of electrons in a conductor

### Amasci: Misconceptions the speed of electrons https://learn.sparkfun.com/tutorials/what-is-electricity

# Charging by friction and contact

### Notice how only the negative charges (electrons) are free to move.

Notice that the spark is MOVING electrons. They are “dynamic”, not “static” (the word ‘static’ means not moving) Thus physicists note that the name for this phenomenon is a misnomer.

### Yet it would look/feel the same as it did in the first example. He can’t tell whether charges jumped to or from him.

text above adapted from Science Joy Wagon 1999

### Notice how the unbalanced electrical charges in the balloon cause the charges on the wall’s surface to (slightly!) move? Polarization ## Contrast : charging by Conduction, and by Induction

These images are from Charging by Electrostatic Induction: Science Joy Wagon

### The first charge is strong but gets weaker each time the electroscope is recharged. (original object is giving up some charge every time it is touched.) ## 32.7 Charge Polarization * ## Electric dipoles

### Water Enter a captionhttp://ch301.cm.utexas.edu/section2.php?target=imfs/vsepr/shape-dipole.html

### CO2 http://ch301.cm.utexas.edu/section2.php?target=imfs/vsepr/shape-dipole.html

Conceptual Physics PowerPoints PowerPoints by Book and Chapter

## Learning Standards

Massachusetts 2016 Science and Technology/Engineering (STE) Standards

HS-PS2-4. Use mathematical representations of Newton’s law of gravitation and Coulomb’s law to both qualitatively and quantitatively describe and predict the effects of gravitational and electrostatic forces between objects.
HS-PS3-2. Develop and use a model to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles and objects or energy stored in fields [e.g. electric fields.]
HS-PS3-5. Develop and use a model of magnetic or electric fields to illustrate the forces and changes in energy between two magnetically or electrically charged objects changing relative position in a magnetic or electric field, respectively.

### Learning Standards: Common Core Math

• CCSS.MATH.CONTENT.7.EE.B.4  Use variables to represent quantities in a real-world or mathematical problem, and construct simple equations and inequalities to solve problems by reasoning about the quantities.
• CCSS.MATH.CONTENT.8.EE.C.7  Solve linear equations in one variable
• CCSS.MATH.CONTENT.HSA.SSE.B.3  Choose and produce an equivalent form of an expression to reveal and explain properties of the quantity represented by the expression. (including isolating a variable)
• CCSS.MATH.CONTENT.HSA.CED.A.4  Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. For example, rearrange Ohm’s law V = IR to highlight resistance R.
• http://www.corestandards.org/Math/

### Common Core State Standards (Inverse-square law)

CCSS.Math.Content.7.RP.A.2a ( Grade 7 ): Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.
CCSS.Math.Content.7.RP.A.2c ( Grade 7 ): Represent proportional relationships by equations.
CCSS.Math.Content.7.RP.A.3 ( Grade 7 ): Use proportional relationships to solve multistep ratio and percent problems.