1. Going over Friday’s Quiz

2. Announcement Absent on Thursday for Certification Exam
Two homework assignments due Friday: Electrostatic Force + Electric Field
Quiz on Friday on Objectives 6-10 (inspired by homework questions)

4. Electrical Forces
Coulomb’s Law

5. Opposite charges ATTRACT
Electrostatic Force
Same charges REPEL + +
Opposite charges ATTRACT - +

6. Electrostatic Force r q1 q2 Amount of force depends on: Fe r
CHARGE ON EACH OBJECT
DISTANCE BETWEEN OBJECTS
ELECTROSTATIC CONSTANT: k = 8.99 x 109 N·m2/C2 q1 q2 Fe r r

7. Electrostatic vs. Gravitational Force
Consider two electrons that are 1.0 micrometer apart.
Gravitationally ATTRACTED
Electrostatically REPELLED Fe e- e- Fg
r = 1.0 μm
5.54 x N
2.30 x N

8. Example #1
Determine the electrostatic force between an object with a +2.0 coulomb charge and an object with a -2.0 coulomb charge if they are separated by 2.0 meters.
ATTRACTIVE

9. Example #2
Determine the electrostatic force between an object with -2.0 micro-coulombs of charge and an object with -5.0 micro-coulombs of charge if they are separated by 5.0 nanometers.
REPULSIVE

10. 1. When two spheres, each with charge Q are positioned a distance R apart, they are attracted to one another by a force of magnitude F. What force would they be attracted by if…
a) one of the charges is tripled while the other is doubled?
b) the separation distance is changed to 3R?
c) one of the charges is changed to Q/2?
d) one of the charges is doubled and the separation distance is R/2?
2) If two charged objects are attracted to one another by an electrostatic force of 5.0 Newtons, what force would they be attracted by if the charge on both of them were doubled?

11. 1. When two spheres, each with charge Q are positioned a distance R apart, they are attracted to one another by a force of magnitude F. What force would they be attracted by if…
a) one of the charges is tripled while the other is doubled? 6F
b) the separation distance is changed to 3R? F/9
c) one of the charges is changed to Q/2? F/2
d) one of the charges is doubled and the separation distance is R/2? F/2
2) If two charged objects are attracted to one another by an electrostatic force of 5.0 Newtons, what force would they be attracted by if the charge on both of them were doubled? 20N