1. Electrostatics Chapter 17

2. Types and Sources of Charge • Positive (proton) and negative (electron) • Charges stem from ionized atoms. Those with too few electrons are positively charged, those will too many negatively charged • Electric charge is conserved • Electric charge is quantized

3. Conductors • Loosely bound electrons in the outermost shell • Electrons can easily move from one atom to the next, allowing charges to be lost or gained easily and current to flow. • Metal • Salt Water

4. Insulators • All electrons are tightly bound • Requires large amounts of energy for charge to change or to move. • Rubber • Pure Water • Air

5. Charging by Friction • Rubbing two objects together to transfer electrons from one object to another. • Led to the discovery of charge • Elektron means amber in Greek

6. Charging by Conduction • Grounding-a method of discharging where a charged object is touched against a much larger neutral object.

7. Charging by Induction

8. Balloons

9. Coulomb's Law • k=8.99x109 Nm2/C2 • Inverse square • Almost exactly the same as Newton’s Law of Universal Gravitation • q is measured in Coulombs (huge) • F will be positive with like charges and negative with unlike charges; therefore positive means repulsive and negative means attractive.

10. Practice Problems • Two charges are 1.2m apart. If the first has a charge of 6μC and the force between them is .45N, what is the charge of the second?

11. 2D Coulomb’s Law • Charges A, B, and C form a right triangle. Charge A is 3C, charge B is 2.5C, and charge C is -7C. The distance between A and B is 4.7m and between B and C is 3m. What is the force on each charge?

12. Electric Fields • The equivalent to g when discussing gravity. • In order to determine electric field, place a positive test charge near other charges and measure the force. • The electric field is independent of the size of the test charge, like g is independent of the mass of an object.

13. Electric Field for a Point Charge • When the electric field is caused by a point charge, we can substitute out force by using Coulomb’s Law

14. Practice Problems • If charge A is 6μC and charge B is -4μC, what is the electric field at point C?

15. Electric Field Lines • Show what the electric field looks like in a specific direction • Direction of lines show direction • Spacing of lines show strength

16. Two Charge Systems

17. Current • Measures how much charge passes a point in a certain amount of time. • Measured in Amperes, or Amps (A)

18. Electric Potential Energy • Like a mass has a potential energy in a gravitational field, a charge will have potential energy in an electric field. • As the charge moves, electric potential energy becomes kinetic energy.

19. Potential Difference • Since we are usually dealing with large quantities of moving charge rather than a single stationary charge, it is easier to discuss a change. • Potential difference=voltage • Measured in volts • Found by finding the difference in potential energy between two points for a test charge and then dividing by the test charge.

20. Resistance • A measure of how much an object resists the flow of electricity. • Electrons move from atom to atom. In the process, energy is lost in heat. • The higher the waste, the more the resistance. • Depends on material, temperature, and shape (thickness and length) • Symbol is R • Unit is the Ohm (Ω)

21. Ohm’s Law • Relates resistance, current, and voltage. • Good for some objects, but not all objects (diode). • Power equation-relates the rate at which energy is converted from electrical energy to mechanical energy to factors in the circuit.

22. Electric Power