1. Electrostatics experiments Helped to develop the model of the atom

2. Electroscope Demo 1 not touching +++++++++ + - + - - - - - + - - - - - + - + + + + Induction : induce a separation of charges (just assume charge is pos. on rod at this point)

3. Electroscope demo 2 ++++++++ + ++ Conduction of charges + +

4. Electrons (and protons) have a “charge” The magnitude of the charge is the same for both protons and electrons Charges are conserved (recall redox from chem..??? I hope so!!!!) Like charges repel – opposite charges attract Charges are quantized - carry a specific amount of energy

5. Recall Newton’s law of gravity – for the force of attraction between 2 bodies? Fg = GMm/r 2

6. Coulomb’s Law describes the force of attraction – or repulsion – between 2 charged particles. F ele = K Q q /r 2 K is a constant = 8.99 x 10 9 (N)m 2 / C 2 Q and q are the respective charges on the particles - units are Coulombs *** 1 C is an enormous charge The charge on one electron is: -(1.60 x 10 -19 C) Same on a p+ (just a positive charge) Notice how Force is related to distance!

7. NOTE When calculating the F net of multiple charges, break into x and Y coordinates (all in one plane)

8. Question 1 How many electrons are needed to establish a charge of 1 C? That is correct! 6.25 x 10 18 e- s Needless to say, 1C is a very large charge!

9. One other thing: Conductor: a material in which a charge moves freely Insulator: a material in which a charge does not move freely

10. Another fun question for you What is the force of attraction between 2 point charges (charges of +1C and -1C) separated by a distance of 1km? That is correct! 9.0 x 10 3 N (that is ~ 2000lbs.)

11. One more fun one What is the velocity of an electron around the proton in the nucleus of a hydrogen atom (If the distance between them is 5.29 x 10 -11 m)? Hint: Set F c = F ele Did you calculate 2.19 x 10 6 m/s? Great job!!!

12. 2 protons 10 -10 m apart Mass of a proton = 1.67 x 10 -27 Kg What is the gravitational F of attraction between the 2 particles? What is the electrostatic F of repulsion between the 2 particles? Fg = ~ 2 x 10 – 44 N (pulling together) Fe = ~ 2 x10 – 8 N = much larger F !!!!! Pulling apart nucleus (stays together due to strong F)

13. One last fun parallel! F g = mg = GMm /r 2 so g = GM / r 2 F ele = q E = KQq /r 2 so E = KQ / r 2 E = electric field strength How sick is that!!!!!!!!