today 3/10 plates if charge e-field potential hw:“plates of charge” due thursday, 3/13 lab:...
TRANSCRIPT
Today 3/10
Plates if charge E-Field Potential
HW: “Plates of Charge” Due Thursday, 3/13
Lab: “Electric Deflection of Electrons”
+ + + + + + + + + + + + + + + + + +
Looking from farther away
+ + + + +
We call this an “infinite plate.”
Field lines for a positive plate
(+)
is the charge on each square meter of the plate.
Near the plate the field lines must (by symmetry) point directly away from the plate.
How does the field strength at the X’s compare?
Same field line density, same strength!
(+)
Field lines for a plate
(-)
Field lines for a negative plate
Can’t tell if the field is caused by a pos plate below or a neg plate above!
Size of the E-field
For plates:
02
E
For point charges:2r
kqE s
0 = 8.8x10-12 C2/Nm2
k = 9.0x109 Nm2/C2
Note: no dependence on distance
Two Parallel Plates
(+)
(-)
(+)
Two Parallel Plates(-)
(+)
Two Parallel Plates(-)
Enet
(+)
Two Parallel Plates(-)
Enet
Enet
(+)
Two Parallel Plates(-)
Enet
Enet
Enet = 0
Enet = 0
(+)
How big is E?(-)
Enet
(+)
How big is E?(-)
Enet = 0
02E
02
E 0
netE
Enet = 0
(+)
What do the field lines look like?(-)
E = 0 outside!
a. The field at A drops more than the field at B.
b. The field at B drops more than the field at A.
c. The fields at A and B remain that same.
d. The fields at A and B drop by the same amount.
A B
+Q -Q
Points A and B are located as shown between two large uniformly charged parallel plates. Which of the following correctly describes what happens to the electric fields at A and B if the plate on the right is removed?
0 = Q/A
Charged conducting plate
What’s wrong with this picture?
A = Area of one side
L = 0/2
Charged conducting plate
Free charge always goes to surface of conductor.
R = 0/2
L = 0/2
Charged conducting plate
R = 0/2
What is the electric field inside the conductor?
EL = L/20
EL = 0/40
L = 0/2
Charged conducting plate
R = 0/2
What is the electric field inside the conductor?
ER = R/20
ER = 0/40
L = 0/2
Charged conducting plate
R = 0/2
What is the electric field inside the conductor?
The electric field is zero everywhere inside the conductor.