
26-6 Electrical Variables
where
ρ
i
s
t
he
r
esistivity
i
n
Ω m
V i
s
t
he
v
oltage
m
easured
b
y
t
he
v
oltmeter
i
n
V
w
i
s
t
he
w
idth
o
f
t
he
s
ample
b
ar
m
easured
i
n
m
h i
s
t
he
h
eight
o
f
t
he
s
ample
b
ar
m
easured
i
n
m
I
is the current the ammeter measures owing through the sample in A
lʹ is the distance between the two points where the voltmeter wires make contact to the bar, measured in m
Note
th
at
th
e
tot
al
le
ngth
l of th
e
ba
r
is no
t
us
ed
to ca
lculate
th
e
fo
ur-point
re
sistivity:
th
e
le
ngth
lʹ
be
tween
t
he
t
wo
i
nner
c
ontacts
i
s
u
sed
.
26.3.3 Common Experimental Errors
ere are many experimental pitfalls to avoid when making resistivity measurements. e most com-