Download Physics Lecture #25

Tue. Feb. 3 – Physics Lecture #25
Gauss’s Law I: Field Lines and Flux
1. Electric Field Vectors and Electric Field Lines
2. Electric Field and Electric Flux
Think about This:
Discuss with neighbors
(based on 24.21) Consider the field
lines shown. If identical charged
particles are placed at points as
shown at the points 1, 2, and 3 in the
electric field lines, which will
experience the greatest electric
force?
1
2
3
The figure shows a cube of side s in a uniform electric field E. What is the flux
through each of the cube faces a, b, and c with the cube oriented as in (i)?
What about the other faces? What is the net flux through the cube? Repeat for
the orientation in (ii), with the cube rotated 60o.
E
E
b
a
(i)
b
c
a
c
(ii)
A spherical surface surrounds an isolated positive charge, as shown (in crosssection). If a second (positive) charge is placed outside the surface:
a) What happens to the electric field on the surface a the point P between the
charges?
b) What happens to the total electric flux through the surface?
+
+
P
+
c) Return to just the single positive charge. Calculate the flux through the
spherical surface.