1. ELECTRICITY and COULOMB’S LAW
Firdiana Sanjaya ( )
Ana Alina ( )

2. THE FACT OF CHARGE There are 2 kinds of charge : positive and negative
The charge with the same sign will repel each another while the charge with different sign will attract each another
Electric charge is quantified
Charge is conserved

3. THE LAW OF CONSERVATION OF CHARGE
Charge can be created and destroyed, but only in positive- negative pairs.
The Law of conservation of charge states that the net charge of an isolated system remains constant.

4. ELECTROSTATIC CHARGING
Materials are divided into three categories, depending on how easily they will allow charge. These are:
conductors (metals, for example)
semi-conductors (silicon is a good example)
insulators (rubber, wood, plastic for example)

5. ELECTROSTATIC CHARGING
There are three ways that objects can be given a net charge. They are
Charging by Friction
Charging by Conduction
Charging by Induction

6. COULOMB’S LAW
is inversely proportional to the square of the separation r between the particles and directed along the line joining them;
is proportional to the product of the charges q1 and q2 on the two particles;
is attractive if the charges are of opposite sign and repulsive if the charges have the same sign.

7. COULOMB’S LAW
We can express coulomb’s law as the equation below k = 8.99 x 109 Nm2/C2 The law expressed in vector form for the electric force exerted by a charge q1 on a second charge q2 , written F12, is

8. Parallel between Electrostatics and Gravitaty
See the different
Where k = 8.99 x 109 N2 m2/C2
G = 6.67 x N2 m2/kg2

9. Parallel between Electrostatics and Gravitaty
Similarities between electrostatic and gravitational forces:
Both act in a vacuum.
Both are central and conservative.
Both obey an inverse-square law 

10. Parallel between Electrostatics and Gravitaty
Differences between electrostatic and gravitational forces:
Electrostatic forces are much greater than gravitational forces for natural values of charge and mass. For instance, the ratio of the electrostatic force to the gravitational force between two electrons is about 1042.
Gravitational force are attractive for the charge that has the same sign but electrostatic force will repul in the same condition.
Gravitational forces are always attractive, while electrostatic forces may be either attractive or repulsive.

11. Electric Field
An electric field is said to exist in the region of space around a charged object—the source charge.
The electric field E is analogous to g (acceleration).

12. The electric field a distance r away from a point charge is given by:

14. If the electric field at a particular point is known, the force a charge q experiences when it is placed at that point is given by :
F = qE
If q is positive, the force is in the same direction as the field; if q is negative, the force is in the opposite direction as the field.

15. Learning from gravity F = qE ma = qE a = qE/m g = qE/m
uniform gravitational field same thing with charges in a uniform electric field. If you throw a charge into a uniform electric field (same magnitude and direction everywhere), it would also follow a parabolic path.

17. Sounds fancy, but it’s not hard
2.4 ELECTRIC FLUX
Sounds fancy, but it’s not hard
Electric Flux measures how much an electric field wants to “push through” or “flow through” some arbitrary surface area
We care about flux because it makes certain calculations easier.

18. Flux is a measure of the number of field lines passing through an area
Flux is a measure of the number of field lines passing through an area. If we define area as a vector, with its direction perpendicular to the surface

20. Electric Flux: General Definition
Electric Flux through a surface depends on three things:
How strong the E-field is at each infinitesimal area.
How big the overall area A is after integration.
The orientation between the E-field and each infinitesimal area.

21. The plane is perpendicular to the field
Case 1
Easiest case:
The E-field is uniform
The plane is perpendicular to the field
Electric Flux
Flux depends on how strong the E-field is and how big the area is.

22. The plane is not perpendicular to the field
Case 2
Junior Varsity case:
The field is uniform
The plane is not perpendicular to the field
Flux depends on how strong the E-field is, how big the area is, and the orientation of the area with respect to the field’s direction.

23. 2.5 Permittivity
Gauss’s Law

24. 2.6 Applying Gauss’s Law
Gauss’s Law can be used to
(1) find the Electric field at some position relative to a known charge distribution, or
(2) to find the charge distribution caused by a known Electric field.

25. The E-field is zero over the surface (or some portion of the surface)
Choose a surface such that…
Symmetry helps: the E-field is constant over the surface (or some part of the surface)
The E-field is zero over the surface (or some portion of the surface)
The dot product reduces to EdA (the E-field and the dA vectors are parallel)
4. The dot product reduces to zero (the E-field and the dA vectors are perpendicular)

26. The E-field is zero over the surface (or some portion of the surface)
Choose a surface such that…
Symmetry helps: the E-field is constant over the surface (or some part of the surface)
The E-field is zero over the surface (or some portion of the surface)
The dot product reduces to EdA (the E-field and the dA vectors are parallel)
4. The dot product reduces to zero (the E-field and the dA vectors are perpendicular)