Chapter 18 & 19 Themal and electrical properties

Question 1

what are the formulas for the current density

Answer 1

J =  E =  (V/

Question 2

what does this formula do V=IR

Answer 2

v = voltage
I = current
R = Resistance

Question 3

what does the variable P stand for ?

Answer 3

Resistivity - A Material property

Question 4

what does this formula Do p= (R A )/ I

Answer 4

p= Resistivity
R= Resistance
A= Area
I = length

Question 5

what does the Variable J equal?

Answer 5

current density = f E = f (V/f )

electric field potential = V/l

Question 6

what magnitude ( 10 ^ n )is the conductivity
of metals ?

Answer 6

10 ^ 7

Question 7

what happens to atoms electrons when the atoms become close together

Answer 7

They form energy bands, where each atom has a discrete energy with a very small difference between adjacent atoms.

Question 8

The arrangement of what band directly influences the arrangement of a Solid material ?

Answer 8

The outer most electron band.

Question 9

what is a partially filled band?

Answer 9

A Band that is layered from bottom to top filled band, partially filled band, band gap, empty band.

Question 10

What is the difference between a Overlapping band and a partially filled band?

Answer 10

Overlapping bands do not have a band gap, and the filled states Overlapp with the empty band,

Question 11

Why are metals in 2A and 3B of the periodic table high conductors?

Answer 11

Because they have overlapping in their P and s band, and the 3 p and 3s band. This permits electrons to be excited into the unoccupied energy levels.

Question 12

What makes an insulator?

Answer 12

A wide band gap (> 2eV )

Question 13

what makes a semi conductor?

Answer 13

A narrow band gap (< 2eV )

Question 14

What is drift velocity?

Answer 14

average velocity in the direction of the forces imposed on the applied field

Question 15

what does this formula do 𝜐𝑑 =𝜇𝑒 f

Answer 15

𝜐𝑑 = average velocity in the direction of
the force imposed by the applied field.
𝜇𝑒= electron mobility; indicative of the
scattering events (m2/Vs)
f = electric field potencial

Question 16

what is the symbol for conductivity?

Answer 16

𝜎 (sigma)

Question 17

What does this formula do? 𝜎 =𝑛|𝑒|𝜇𝑒

Answer 17

𝜎: electrical conductivity
n: number of free electrons
|e|: electron charge
𝜇e: electron mobility

Question 18

what are the four things that increase metal resistivity?

Answer 18

Presence of imperfections, temperature, impurities, and cold working.

Question 19

what is the difference between electrical properties of intrinsic and extrinsic semiconductors?

Answer 19

intrinsic: Same as pure material
Extrinsic: dictated by imparity atoms

Question 20

What are the two types of electronic charge carriers?

Answer 20

a free electron (negative charge)
a hole (positive charge)

Question 21

what is this formula 𝜎 =𝑛|𝑒|𝜇𝑒 + p|𝑒|𝜇h

Answer 21

𝜎 = conductivity
𝑛 = number of free electrons
𝑒 = electrical charge
𝜇𝑒 = electron mobility
p = number of holes
𝜇h = hole mobility

Question 22

in an intrinsic semiconductor the number of electrons = ?

Answer 22

the number of holes

Question 23

in an extrinsic semiconductor does the number of holes equal the amount of free electrons?

Answer 23

NO

Question 24

does a p or a n type extrinsic semiconductor have more holes or free electrons?

Answer 24

n-type has more electrons!

Question 25

in intrinsic semiconductors, does conductivity increase or decrease with temperature

Answer 25

increase

Question 26

When impurity atoms are added to extrinsic semiconductors does the conductivity increase or decrease?

Answer 26

increase as imperfection sites lower the
activation energy to produce mobile electrons

Question 27

what is the heat capacity

Answer 27

energy stored as atomic vibrations required to increase a mole of material by a unit T

Question 28

what is the coefficient of thermal expansion? which material has the highest values?

Answer 28

the size of a material changes with a change in temperature
* polymers have the largest values

Question 29

What is Thermal conductivity? Which material has the highest value?

Answer 29

the ability of a material to transport heat
* metals have the largest values

Question 30

what is this formula? C = ∆Q / ∆T

Answer 30

C = Heat capacity
∆Q = change in energy (energy input)
∆T = change in temperature

Question 31

what is the Debye temperature?

Answer 31

the temperature where energy is no longer stored as waves

Question 32

what does this formula do (lf - li) / li = αl * (Tf - Ti)

Answer 32

lf = length final
li = length initial
al = thermal expansion
Tf = temperature final
Ti = temperature inital

Question 33

what does this formula do q = -k ( ∆T / ∆x)

Answer 33

q = heat flux
∆T = change in temperature
∆x change in length
NOTE THAT ( ∆T / ∆x) is temperature gradient