1. Electrostatics
Electrostatics- study of charges that can be collected in one place (static electricity)
Electric charge, the forces between them, and their behavior in materials
Charged particles are not created but can be separated
Electrons can be removed from or added to atoms.
Mass? Matter?
Moving electric charges = Current (Big Picture!)
Ex. Bonding of atoms

2. Charges
Electrons?
Protons?
Where are they located?

3. Charges Electric Charge is quantized (it has a value).
called the Coulomb
An electron has a charge of
-1.6 x C
An proton has a charge of
+1.6 x C
One Coulomb has the same charge as 6.25 x electrons (see conversion/calc)
about the amount of charge that passes through a 100W light bulb in 1 second (Static shock = 1 µC)

4. Electric forces What happens when two like charges come together?
Unlike charges?

5. Coulomb’s Law F = kq1q2/r2 k is Coulomb’s constant = 9 x 109 N-m2/C2
q is the charge (q = test charge)
r is the distance between the charges to their center of mass
note this follows the inverse square law

6. Electric forces
Which is stronger the force of gravity (weight) or the force between electrons and protons?

7. Coulomb’s Law Example I
Anthea rubs two latex balloons against her hair, causing the balloons to become charged negatively with a charge of 2.0 x 10-6 C. She holds them a distance of .70 m apart. A. What is the electric force between the two balloons? B. Is it a a force of attraction or repulsion?

8. Coulomb’s Law Example II
Bonnie is dusting the house and raises a cloud of dust particles as she wipes across the table. If two 4.0 x C pieces of dust exert an electrostatic force of 2.0 x N on each other, how far apart are the dust particles at that time?

9. Superposition: Configurations of 3 or more charges
If a particular charge encounters two or more electrostatic interactions, then the net electric force is the vector sum of those individual forces.
+/- charges are non-significant for this process
ONCE AGAIN, the direction of forces are dictated by repulsion/attraction
1 µC = 10-6
Remember ΣF’s(Rememeber, Forces are vectors)

10. Example: A –6 mC charge is placed 4 cm from a +9 mC charge
Example: A –6 mC charge is placed 4 cm from a +9 mC charge. What is the resultant force on a –5 mC charge located midway between the first charges?
1. Draw and label. - +
2 cm
+9 mC
-6 mC q1 q2 r2 r1 F1 F2
2. Draw forces. q3
3. Find resultant; right is positive.
F1 = 675 N
F2 = 1013 N

11. Example (Cont.) Note that direction (sign) of forces are found from attraction-repulsion, not from + or – of charge. + - +
2 cm
+9 mC
-6 mC q1 q2 r2 r1 q3 F2 F1
F1 = 675 N
F2 = 1013 N
The resultant force is sum of each independent force:
FR = 1.69 x 10^3 N
FR = F1 + F2 = 675 N N;

12. Conductors and Insulators
Insulators- materials through which charges will not move easily. Ex. Glass, dry wood, most plastics , cloth, rubber, and dry air. Conductors- materials that allow charges to move about easily. Ex. Metals

13. Electrostatic Induction
Action in which a charged object causes charges on another object (sometimes neutral) to realign.

14. Polarization Separation of Charge
When a charged object is brought next to a neutrally charged insulator, polarization occurs.
The Result of Electrostatic Induction
The presence of a charged object will cause another object’s charges to realign. One side of the object will be more positive and the other more negative.
balloon stuck to the board, copier machine, batteries etc…

15. Conduction & Grounding
An object is considered to be grounded if it is attached to the Earth.
Grounded: attaching an object to the Earth to eliminate excess charge.
Your body could be a conductor of charges to the ground

16. Induction Example

17. Electric Fields A property of space predicting force
An Area of influence around a charged object. The ratio of the force of a charge to the test charge (positively charged particle placed in the field used to predict the direction of the charge)
Electric fields around a charge are represented by vectors
A vector quantity away from is “+” and towards is “-”
Equation: E = F/q or (E = kQ/r2)
measured in N/C
Manipulation for Fe = qE (Think Fg = mg)

20. Electric Field Example
Mr. Drechsel is photocopying lab sheets for his first period class. A particle of toner carrying a charge of 4.0 x 10-9 C in the copying machine experiences an electric field of 1.2 x 106 N/C as it’s pulled toward the paper. What is the electric force acting on the toner particle?

21. Electrical Potential Difference A property of space predicting energy
The energy a charge possesses by virtue of its location
The work done to move a positive test charge from one location to another – This is Energy!
“Voltage”
V = W/q
measured in J/C or V (volts)

22. Potential Energy Example
An electron in Tammie’s TV is accelerated toward the screen across a potential difference of 22,000 V. How much kinetic energy does the electron lose when it strikes the TV screen?

23. Electric Potential in a Uniform Field
The “field” that exists between two charged parallel plates is uniform and depends on the potential difference between the plates and the plate separation
Electric Field = Potential Difference/distance
E = V/d
Units??? E = volt/meter or Newton/Coulomb???

24. Potential Difference Example
While getting out of a car, Victor builds up a charge on his body as he slides across the cloth car seats. When he attempts to shut the car door, his hand discharges 12,000 V through a uniform electric field of 3.0 x 106 V/m. How far is his hand from the door at the time the spark jumps?

25. Sharing of Charge Capacitors- store charge
Capacitance- the ratio of charge stored to potential difference.
Equation: Capacitance = q / V
Unit: Farad ( 1 Coulomb per Volt)