PASCO EM-8812 Resistance Apparatus - Manual (Page 16)

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R e s i s ta n c e A p p a r a t u s T e a c h e r s ’ N o t e s a n d T y p i c a l D a ta
16
Part D
This table shows data for wires of other materials with =24 cm.
Experiment 2: Resistance versus Length
This graph shows V versus I for the largest brass
wire (A = 0.0127 cm
2
) with = 24 cm, 20 cm,
16 cm, 12 cm, 8 cm, and 4 cm. The slope of
each line equals R.
This graph shows R versus for the largest brass
wire (where R was taken from the slopes in the
first graph). The slope equals
ρ/A; thus,
ρ = 7.11 µΩ·cm.
The table below shows ρ determined in this way for all wires. For the four brass samples, the average value of ρ
is 7.21
µΩ·cm with a standard deviation of about 0.1 µΩ·cm (1.4%).
D (cm) V (mV) I (A) R (m
Ω) ρ (µΩ·cm)
Copper 0.10 5.19 0.997 5.21 1.76
Aluminum 0.10 14.5 0.994 14.6 4.93
Brass 0.10 21.3 0.990 21.5 7.27
Nichrome 0.10 161 0.504 319 108
Stainless Steel 0.10 232 0.994 233 78.8
A (cm
2
) slope =
ρ/A (mΩ/cm) ρ (µΩ·cm)
Brass
0.0127 0.561 7.11
0.00811 0.886 7.18
0.00519 1.39 7.21
0.00203 3.62 7.34
Copper 0.00811 0.222 1.80
Aluminum 0.00811 0.595 4.82
Nichrome 0.00811 13.2 107
Stainless Steel 0.00811 9.70 78.6