Lauren McCarthy
Section G Red
4/19/10
Chapter 15: Electric Forces and Fields
 The SI unit of charge is the Coulomb (C)
- e = 1.6 x 10-19 C
Conductors are materials in which the electric charges move freely in response to an electric force
 Copper, aluminum and silver are good conductors
Insulators are materials in which electric charges do not move freely
 Glass and rubber are examples of insulators
Coulomb’s Law
q1 q2 applies only to point charges
F  ke
9
2
2
r2
ke = 8.9875 x 10 N m /C
An electric field exists in the region of space around a charged object
E
kQ
F
 e2
qo
r
SI units = N/C, vector quantity,
Chapter 16:
Potential difference: ΔV = VB – VA = ΔPE / q, ΔPE = q ΔV – scalar quantity, v= J/C units
The point of zero electric potential is taken to be at an infinite distance from the charge,
The potential created by a point charge q at any distance r from the charge is
q
V  ke
PE  q2V1  ke
r
q1q2
r
Since W = -q(VB – VA), no work is required to move a charge between two points that are at the same
electric potential W = 0 when VA = VB
The electron volt (eV) is defined as the energy that an electron gains when accelerated through a
potential difference of 1 V-> 1 eV = 1.6 x 10-19 J
A capacitor is a device used in a variety of electric circuits. The capacitance, C, of a capacitor is defined
as the ratio of the magnitude of the charge on either conductor (plate) to the magnitude of the
Q
potential difference between the conductors (plates)
units- Farard (F)= 1 C/V
C
V
Chapter 17:
Q
The current is the rate at which the charge flows through this surface
I 
t
 The SI unit of current is Ampere (A), 1 A = 1 C/s
I = ΔQ/Δt = nqvdA
Units of resistance are ohms (Ω)--1 Ω = 1 V / A
L
Ohm’s Law: ΔV = I R, resistance of a ohmic conductor = R  
A
Chapter 18:
The source that maintains the current in a closed circuit is called a source of emf
 Any devices that increase the potential energy of charges circulating in circuits are
sources of emf, units = Volts
Kirchhoff’s Rules: Junction Rule & Loop Rule
The sum of the currents entering any junction must equal the sum of the currents leaving that junction
The sum of the potential differences across all the elements around any closed circuit loop must be zero