Physics 212
Midterm 2
Form A
1.
A wire contains a steady current of 2 A. The charge that passes a cross section in 2 s is:
A.
3.2 × 10
-19
C
B.
6.4 × 10
-19
C
C.
1 C
D.
2 C
E.
4 C
2.
In a Physics 212 lab, Jane measures the current versus voltage characteristics for two nichrome
wires and makes the graph shown. The wires are of the
same diameter
but have
different
lengths
. Which of the following statements is correct?
3.
The current density across a cylindrical conductor of radius
R
varies according to the equation
J
=
J
0
(
r
/
R
), where
r
is the distance from the central axis. Thus, the current density is zero at the axis (
r
= 0) and increases linearly to
J
0
at the surface (
r
=
R
). Calculate the current in terms of
J
0
and
R
.
A.
i
= (
π
R
2
J
0
)/2
B.
i
= (2
π
R
2
J
0
)/3
C.
i
= (
π
R
2
J
0
)/6
D.
i
= (
π
R
3
J
0
)/3
E.
i
= (
π
R
3
J
0
)/6
4.
A wire is 1 m long and 1 × 10
-6
m
2
in cross-sectional area. When connected to a potential
difference of 2 V, a current of 4 A exists in the wire. The
resistivity
of the wire material is:
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