A lead rod with a circular cross section has a length of 37.5 cm and a resistance of 4.35 μΩ. The data provided in the table may be useful.
Conductivity (σ), resistivity (ρ), and temperature coefficient of resistivity (α) at 20°C for select materials.
material
conductors
σ (1/(Ω·m))
ρ (Ω·m)
α (C⁻¹)
silver
6.29 × 10⁷
1.59 × 10⁻⁸
3.8 × 10⁻³
copper
5.95 × 10⁷
1.68 × 10⁻⁸
3.9 × 10⁻³
gold
4.10 × 10⁷
2.44 × 10⁻⁸
3.4 × 10⁻³
aluminum
3.77 × 10⁷
2.65 × 10⁻⁸
3.9 × 10⁻³
tungsten
1.79 × 10⁷
5.60 × 10⁻⁸
4.5 × 10⁻³
iron
1.03 × 10⁷
9.71 × 10⁻⁸
6.5 × 10⁻³
lead
0.45 × 10⁷
22.0 × 10⁻⁸
constantan
0.20 × 10⁷
49.0 × 10⁻⁸
0.03 × 10⁻³
mercury
0.10 × 10⁷
98.0 × 10⁻⁸
0.9 × 10⁻³
nichrome
0.10 × 10⁷
100. × 10⁻⁸
0.4 × 10⁻³
semiconductors
(Values for semiconductors depend strongly on type and amount of impurities.)
carbon (pure)
2.86 × 10⁻⁶
3.50 × 10⁻⁵
-0.5 × 10⁻³
germanium (pure)
0.60
-0.048
silicon (pure)
2300
-0.075
What is the radius, in centimeters, of the rod?
r = ____ cm