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PHY 2049C – General Physics B
Fields, Circuits, Waves, Light
Today:
1) Gauss' Law
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View Full Document Question 1
Imagine a sphere in a region of uniform electric
field. The net electric flux through the sphere is
(A) zero
(B) positive
(C) negative
(D) undetermined
Gauss' Law
A closed surface around charges is crossed by
as many field lines as the
net charge
inside it.
Left : 0
(count field lines leaving +, entering )
Right: +8
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View Full Document Gauss' Law
The
net flux
through any closed surface equals
4
π
k
times the
net charge inside
the surface.
with
This is the first of Maxwell's 4 equations.
It holds for any shape or form of closed surface and
any distribution of charges inside.
It works wonders in “symmetric” situations.
0
4
inside
net
N
inside
S
Q
EdA
kQ
π
ε
Φ=
=
=
∫∫
12
2
2
0
1
8.85 10
/
4
CN
m
k
−
==
×
Electric Flux
How do we measure the
number of “Field Lines”
crossing a surface ?
Quantitative:
“Electric Flux”
If E crosses A “head on”
If E crosses A at angle:
(surface normal vector
)
E
N
is field component normal to
surface A
&
n
EA
Φ=
cos
N
EA
E
A
θ
=
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View Full DocumentProblem Solving with Gauss' Law
Gauss law was made for symmetries !
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This note was uploaded on 06/29/2010 for the course PHY2049C PHY2049C taught by Professor Duke during the Summer '10 term at FSU.
 Summer '10
 DUKE

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