Electrical/thermal properties

Question 1

Ohm’s law

Answer 1

V=IR

Question 2

Relationship between resistivity and conductivity

Answer 2

O’ = 1/P

O’ = conductivity
P = resistivity

Question 3

Range of conductivity between materials (Ohm-m)^-1

Answer 3

Conductors: 1-6.8x10^7
Semiconductors: 10^-6 -> 4x10^-4
Insulators: 10^-17 -> 10^-9

Question 4

In terms of electron band structure, discuss reasons for difference in conductivity among metals, semicons, insulators.

Answer 4

Metals: -partially filled bands
-overlapping empty bands
Insulators : -wide band gap (>2eV)
-few electrons excited across band gap
Semicons: -narrow band gap (<2eV)
-more electrons excited

Question 5

Describe drift velocity/ mobility of a free electron

Answer 5

Drift velocity: avg V in the direction of F app imposed on the app field
Electron mobility: how easily electrons can move in response to an electric field

Question 6

Factors that influence resistivity

Answer 6

• temperatures (increase atomic separation)
  -imperfections (scatter electrons so they take a less direct path)

Question 7

Why are semiconductors useful, list examples

Answer 7

• unique intrinsic, extrinsic properties allows the development of diodes and transistors in replacement of vacuum tubes, miniturizing circuits

Question 8

Compare intrinsic/ extrinsic semicons, list examples for each

Answer 8

Intrinsic: electrical properties of the pure material (not controlled by impurities)
- silicon/germanium
Extrinsic: elec properts determined by impurities which introduce excess electrons/holes
-SiP, SiB

Question 9

Expression for conductivity of intrinsic semicons

Answer 9

o’= n|e|ųe + p|e|ųh
o’ = conductivity
n, ųe = electron side
p, ųh = hole side
e = Coulomb’s constant

Question 10

Expression for extrinsic semicons:

Answer 10

o’ ~ n|e|ųe (n-type)
o’ ~ p|e|ųh (p-type)

Question 11

Compare n-type and p-type

Answer 11

n-type : more electrons than holes
p-type: more holes than electrons

Question 12

What is heat capacity, Cp and Cv

Answer 12

-Ability of material to absorb heat
-HC at constant pressure
-HC at constant volume

Question 13

what is linear coef of thermal expansion/ volume coef of thermal expansion

Answer 13

Al = delta (L)/ Li (Tf-Ti)
Av = delta (V)/ Vi (delta T)

Question 14

How do atoms influence thermal expansion

Answer 14

As atoms move more, they bump into each other and push each other away -> results in thermal expansion