Transcript W5D2 - UCF Physics

We learned about charge and got a conceptual feel for
what it is.
 We identified charge with the fundamental building clocks
of atoms.
 We studies charge transfer from a number of perspectives.
 We looked at polarization of insulating materials
 We learned about conductors and what actually moves.
 We learned how to make someone’s hair stand on end.
 We learned about how to stick a balloon to a wall.
 We learned how to understand these effects.


At least you
should have learned these things.
An aluminum nail has an excess charge of +3.2 µC. How
many electrons must be added to the nail to make it electrically
neutral?
A) 2.0 × 1013
B) 2.0 × 1019
e=1.60217646 × 10-19 coulombs
16
C) 3.2 × 10
D) 3.2 × 106
E) 5.0 × 10–14
q1q2
F k 2
r
F is a VECTOR and is positive
if the two charges repel and
negative if they attract.
How do F21 and
F12 compare?


Unit Charge


etc.

E

qn
k 2
rn

Then add ‘em up as vectors
Three point charges have equal magnitudes, two being positive and one
negative. These charges are fixed to the corners of an equilateral triangle, as
the drawing shows. The magnitude of each of the charges is 5.0 mC, and the
lengths of the sides of the triangle are 3.0 cm. Calculate the magnitude and
direction of the Electric Field on charge C. (diagram)
And then there was Gauss
How much flux leaves the sphere??
A None
B q
q
C
0
D q 0
E Depends on the shape.
q
 TOTAL FLUX 


LEAVING
ANY

  Total 
CLOSED VOLUME 

i 
Enclosed Charge
0
Gauss’s Law
    E ( A )
  E  A  EA  E (4 R )

i
i
2
i

q
4 0 R 2
4 R 2 
q
0
Two spherical shells have a common center. +q
charge is spread uniformly over the inner shell,
which has a radius of 0.050 m. A + 8q charge is
added to the outer shell, which has a radius of 0.15
m. Find the magnitude and direction of the
electric field at the following distances (measured
from the common center).
(a) 0.20 m
(b) 0.10 m
(c) 0.025 m
q
Potential Energy