Classical Physics II
PHY132
Lecture 26
Li
ht R
di ti
d Q
t
Ph
i
Light, Radiation, and Quantum Physics
Lecture 26
1
04/09/2010

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Maxwell’s Equations
F
ti
t
th
l t l
d
ib ll th
t
i l
d
Four equations together completely
describe all the material covered
so far (i.e. all of electromagnetism);
they are called Maxwell’s Equations:
on the direct sources of E and B:
–
Gauss’ Law for
E
:
(our workhorse for the
E
-field)
–
Gauss’ Law for
B
:
(no magnetic monopoles)
encl
0
d
Q
E
A
0
d
B
A
on the deep connections
between
E
and
B
:
–
Ampere’s Law:
(with Maxwell’s
i
D
)
–
Faraday’s Law:
(with Lenz’ Law)
0
Charge
0
encl.
E
d
i
d
dt
B
l
d
d
dt
E
l
E
Faraday s Law:
(with Lenz Law)
•
note: symmetry would be perfect if magnetic
mono
poles and currents of monopoles existed …
Maxwell showed that these 4 laws predict the existence of ELECTRO-
MAGNETIC waves propagating through vacuum
B
MAGNETIC waves, propagating through vacuum,
at the speed of light
c=
1/
√
(
ε
0
μ
0
)
–
This was revolutionary at the time:
waves
were only thought to
t
i
MEDIUM
Lecture 26
2
propagate
in a MEDIUM
…
–
Maxwell postulated the AETHER as the medium for EM waves…
with
very weird properties …
04/09/2010