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Energy Stored in Electric Fields
Energy is stored in the
capacitor:
A
C 0
and V  Ed
d
1
2
U  C  V 
2
V
+
E
1  0 A 
2
U 
  Ed 
2 d 
1
U    0 Ad  E 2
2
The “volume of the capacitor” is Volume=Ad
-
+Q
d
-Q
area A
Energy stored per unit volume (u):
V
+
1
 0 Ad  E 2 1 2
u 2
 0 E
Ad
2
The energy is “stored” in the electric
field!
-
E
+Q
d
-Q
area A
“The energy in electromagnetic phenomena is the same as mechanical
energy. The only question is, ‘Where does it reside?’ In the old theories, it
resides in electrified bodies. In our theory, it resides in the electromagnetic
field, in the space surrounding the electrified bodies.”—James Maxwell
1
u  0 E 2
2
This is on page 2 of your OSE
sheet. Do not use until later!
(Unless you really know what
you are doing.)
This is not a new “kind” of energy. It’s the
electric potential energy resulting from the
coulomb force between charged particles.
Or you can think of it as the electric energy
due to the field created by the charges.
Same thing.
V
+
-
E
+Q
f
-Q
area A