1. Warm-up Like charges __________ and unlike charges __________

2. Electrostatics

3. What is electrostatics? The study of electrical charges that are held in one place and not in motion –Electro - Electric stuff –Statics - not moving Good in theory, not in practice, because charges don’t like to stay still

4. What is charge? Charge is an electrical attraction or repulsion due to absence or excess of electrons Objects can be either positive, negative, or neutral in charge –Positive --> absence of electrons –Negative --> excess electrons –Neutral --> equal

5. How is charge measured? Charges are represented in Coulombs (C) –One C is equal to the charge of 6.25 x 10 18 electrons

6. Conductors and Insulators Conductors –Easily conduct electricity –Charges easily move –Metals (copper, aluminum, etc) Insulators –Don’t conduct electricity –Charges don’t easily move –Glass, dry wood, most plastic, dry air

7. What about air? (don’t need to write down) Dry air is a good insulator –Doesn’t conduct electricity well –About 33 kV/cm Moist or wet air conducts better –Electrons can escape through the water in the air *Old house story (then generator)

8. Coulomb’s law Positive --> like charges --> repel Negative --> unlike charges --> attract Coulomb’s law describes how like or opposite charges attract or repel F = Force q 1 = charge 1 q 2 = charge 2 d 2 = distance squared

9. What is this k? k = 9.0 x 10 9 Nm 2 /C 2 –Called “Coulomb’s Law Constant” K is related to the permittivity of free space –Basically, how easily charge can communicate though empty areas If there is more than one charge acting on an object, the sum of the forces is the net force

10. Charging stuff Something can be charged in two ways: –Conduction When two items contact to exchange charges –Induction When two items come close but do not touch and charges move in one object to orient the positive and negative charges *Demonstrations

11. Alright…a few whiteboard problems

12. A positive and a negative charge, each of 1.5 x 10 -5 C, are separated by.15 m. Is the force attractive or repulsive? What is the force?

13. Two electrons in an atom are separated by a distance of 1.5 x 10 -10 m. If each electron has a charge of 1.60 x 10 -19 C, what is the force that repels the two electrons? If the mass of an electron is 9.11 x 10 -31 kg, what is the acceleration of the masses if they were set at rest? (reminder a = F/m)

14. A positive charge of 3.0 x 10 -6 C is pulled on by two negative charges, A and B. A is 0.05m to the north with a -2.0x10 -6 C B is 0.03m to the south with a -4.0x10 -6 C What is the force from A? What is the force from B? What is the total force on the charge?

15. A proton and electron have equal and opposite charges of 1.60 x 10 -19 C In a special atom, there are 2 electrons and one proton separated by a 90 o angle with the proton at the vertex. If the distance between the proton and electron is 5.3 x 10 -11 m, –What is the force of one of the electrons on the proton? –what is the net force on the proton?