Web Page. Homework and webassign. All homework is on webassign Key is wfu 2652 3974 . Bookstore can sell you a license, or you can get it online Personalized problems, you need to get correct to 1% or better Link to webassign is on the class web page
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Homework and webassign
http://www.webassign.net/student.html
Labs
Pandemic Plans
Emergency contacts:
Web page
Cell: 33625364645
Background
Prerequisites
SI Units
Fundamental units
Time second s
Distancemeter m
Masskilogram kg
TemperatureKelvin K
Charge Coulomb C
Red boxes mean memorize this, not just here, but always!
Derived units
ForceNewtons Nkgm/s2
EnergyJoule JNm
PowerWatt WJ/s
FrequencyHertz Hzs1
Elec. PotentialVolt VJ/C
CapacitanceFarad FC/V
CurrentAmpere AC/s
ResistanceOhm V/A
Mag. FieldTesla TNs/C/m
Magnetic FluxWeber WbTm2
InductanceHenry HVs/A
Metric Prefixes
109 G Giga
106 M Mega
103 k kilo
1
103 m milli
106 micro
109 n nano
1012 p pico
1015 f femto
Vectors
z
y
vx
vz
vy
x
Finding Components of Vectors
y
v
vy
vx
x
Unit Vectors
Adding and Subtracting Vectors
Multiplying Vectors
Electricity
s
b
b
r
r
z
a
Cleanair
50 kV
q
b
a
+
Dirty air

Electric Fields
Chapter 23
Electric Charge
Particleq
Protone
Neutron0
Electrone
Oxygen nuc.8e
Higgs Boson 0
Red dashed line means you should be able to use this on a test, but you needn’t memorize it
ANS C (also B)
Charge can be spread out
– 3.0 C/cm
2 cm
5.0 C/cm3
A box of dimensions 2 cm 2 cm 1 cm has charge density = 5.0 C/cm3 throughout and linear charge density = – 3.0 C/cm along one long diagonal. What is the total charge?
A) 2 CB) 5 CC) 11 C D) 29 CE) None of the above
1 cm
2 cm
The nature of matter
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Insulators only let their charges move a very short distance
Conductors allow their charges to move a very long distance
Warmup01
Some ways to charge objects
–
–
+
–
+
–
+
–
+
+
–
–
–
–
–
–
–
–
+
–
–
–
–
–
–
–
–
–
–
–
–
–
ANS E
JIT
ANS E
Warmup 01
Coulomb’s Law
q1
q2
Warmup 01
Serway 2315. Three point charges are located at the corners of an equilateral triangle as shown below. Calculate the net electric force on the 7.0 mC charge.
Use superposition
Solve on Board (so take notes).
Sample Problem
+2.0 C
5.0 cm
5.0 cm
–2.0 C
5.0 cm
7.2 N
–2.0 C
7.2 N
JIT Examples 23.3 and 23.4
ANS C
Electric Field
Lightning is associated with very strong electric fields in the atmosphere.
Warmup 02
The Electric Field
q0
r
The units for electric field are N/C
T
Why Do We Use an Idea of Electric Field?
In our everyday life we use to an idea of contact forces:
Example: The force exerted by a hammer on a nail
The friction between the tires of a car and the road
However electric force can act on distances.
How to visualize it?
Even Newton had trouble with understanding forces acting from distances.
Gravitational force is acting on distances
Solution:
Let’s introduce the idea of field.
Earth
GRAVITATIONAL FIELD
ELECTRIC FIELD
+q
m0
Source of field
Source of field
Test charge
Test mass
Electric field is generated and described
by source charge +q.
Test charge q0 is a detector of electric field.
Gravitational field is described by
source mass (mass of Earth).
Test mass m is a detector of
gravitational field.
Test charge q0 <<q, so field is undisturbed.
Definition of an Electric Field
P
q
We have positive and negative charges.
The electric field is defined as the electric force
acting on a positive
test charge +q0 placed at that point divided by test charge:
Direction of an electric field:
+q0
(repulsive force)
P
+q
+q0
(attractive force)
Electric Field from Discrete Distribution of Charges
The electric field at point P due to a group of source charges
can be written as:
Example:
Find an electric field at point P generated by charges q1 =20μC and q2 = 30μC in a distance r1 =1m and r2 =2m from point P, respectively.
y
q1
1m
x
2m
P
q2
These are fictitious lines we sketch which point in the direction of the electric field.
1) The direction of at any point is tangent to the line of force at that point.
2) The density of lines of force in any region is proportional to the magnitude of in that region
Lines never cross.
Warmup02
JIT
Ans A, B, C
Ans B