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Lesson 13: Voltage in a Uniform Field
Most of the time if we are doing experiments with electric fields, we use parallel plates to ensure that
the field is uniform (the same everywhere).
●
This carries over to our study of voltage. If we use parallel plates, then we also get a uniform
change in potential difference.
○
If a charged particle is released between the plates, it will move on its own from an area of
high potential, to an area of low potential.
○
If the charge is moved a distance, d, the change in
electric potential energy
can be found
with…
W = Fd
=> which is the same as =>
ΔE
p
= Fd
Combine that with
V
=
E
q
to get.
..
V
=
E
q
=
Fd
q
=
F
q
d
...and we know that
E
=
F
e
q
so.
..
V
=
E d
Although you can certainly use the formula this way, we see it on the data sheet as.
..
∣
E
∣=
V
d
∣
E
∣
= electric field (N/C)
ΔV = voltage (V)
Δd = distance between locations (m)
This formula is typically applied to situations where parallel plates are being used, since this is the
easiest way to have a uniform electric field.
●
The direction for the field is still determined by the direction a
positive
test charge would move.
●
Also, notice that because of this formula, we can show that the electric field can also be
measured in V/m, not just N/C.
○
Try to prove that the units for V/m are equivalent to N/C .
.. my hint is that you should try to
break all the derived units down to base units.
Example 1
: We have two parallel plates that are 16.0mm apart.
a) If we want a uniform field of 800 N/C between these plates,
determine
the voltage we must
apply to the plates.
∣
E
∣=
V
d
V
=∣
E
∣
d
V
=
800
0.0160
V
=
12.8
V
10/12/2011
© studyphysics.ca
Page 1 of 5 / Section 11.2 & 11.3
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View Full Document b)
Determine
how much work is done if an alpha particle (
info on your data sheet
) moves from
the positive plate to the negative plate.
V
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.
 Fall '08
 Staff
 Electric Fields

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