Download Quiz 1 Solutions

Quiz 1: Electric Fields Lab
Solutions
1/19/2006
10pts
1. (5pts) Derive the electric field strength E in terms of electric potential difference V,
and distance d, using that:
W
V =
(1)
q
We define work as the force required to move a charge a certain distance d
v r
W = F ⋅ d (2)
Where W is work, F is force and d is distance. Substituting Eq. (2) into Eq. (1) we get:
Fd
V =
(3)
q
The force exerted on a particle in an electric field is given by,
F = Eq
(4)
Substituting Eq. (4) into Eq. (3) we find the electric field strength in terms of V and d.
V
E=
(5)
d
2. (5pts) What are the standard units for electric field strength? In what units will we be
measuring electric field strength? Show that the two are equivalent. (Hint: A volts is J/C)
i.
ii.
iii.
N (newtons )
C (Coulomb)
V (volts )
V (volts)
or
In the experiment we measure in
m(meter ) cm(centimeter )
V
J
N ⋅m N
J
=
=
=
where V =
and J = N ⋅ m
m C ⋅m C ⋅m C
C
The standard SI units of electric field are