2.2.4 Resistivity

Question 1

How does resistivity vary with temperature in semiconductors?

Answer 1

Resistivity decreases with increasing temperature as a result of:
1. Increase in electron-ion collision frequency -> increased resistivity
2. More electrons break free of atoms + increase number of electrons available for conductivity - decreasing resistivity.
2nd effect dominates

Question 2

Describe a Fuse and explain how it works.

Answer 2

Made from copper wire and ceramic casing.
Copper has low resistivity but thinness makes it higher, allowing high enough currents to melt it and break the circuit.
Fuses should be rated above max current so device will never blow

Question 3

How does resistivity vary with temp in a metal?

Answer 3

Resistivity increases with increasing temp because increased vibrations of metal ions result in the increase of frequency of collisions.