The temperature coefficient of resistivity of iron is 5.0 10-3 / ...

[Destiiny22]

The temperature coefficient of resistivity of iron is 5.0  10-3 / C; that of carbon is -0.50  10-3 / C. When an iron wire and a carbon rod, each having the same 10 W resistance at 20C, are cooled from that temperature to -80C, the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature is
 a. -0.10.
  b. +1.9.
  c. +2.1.
  d. -10.
  e. +10.

Question 2

If a mile of 24-gauge copper wire has a resistance of 0.14 kW and the resistivity of copper is 1.7  10-8 W  m, what is the diameter of the wire? (1 mile = 1.6 km)
 a. 0.40 mm
  b. 0.50 mm
  c. 0.63 mm
  d. 0.80 mm
  e. 0.25 mm

[juicepod]

Answer to Question 1

C

Answer to Question 2

B