Chapter 18 & 19 Themal and electrical properties Flashcards
what are the formulas for the current density
J = E = (V/
what does this formula do V=IR
v = voltage
I = current
R = Resistance
what does the variable P stand for ?
Resistivity - A Material property
what does this formula Do p= (R A )/ I
p= Resistivity
R= Resistance
A= Area
I = length
what does the Variable J equal?
current density = f E = f (V/f )
electric field potential = V/l
what magnitude ( 10 ^ n )is the conductivity
of metals ?
10 ^ 7
what happens to atoms electrons when the atoms become close together
They form energy bands, where each atom has a discrete energy with a very small difference between adjacent atoms.
The arrangement of what band directly influences the arrangement of a Solid material ?
The outer most electron band.
what is a partially filled band?
A Band that is layered from bottom to top filled band, partially filled band, band gap, empty band.
What is the difference between a Overlapping band and a partially filled band?
Overlapping bands do not have a band gap, and the filled states Overlapp with the empty band,
Why are metals in 2A and 3B of the periodic table high conductors?
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.
What makes an insulator?
A wide band gap (> 2eV )
what makes a semi conductor?
A narrow band gap (< 2eV )
What is drift velocity?
average velocity in the direction of the forces imposed on the applied field
what does this formula do 𝜐𝑑 =𝜇𝑒 f
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
what is the symbol for conductivity?
𝜎 (sigma)
What does this formula do? 𝜎 =𝑛|𝑒|𝜇𝑒
𝜎: electrical conductivity
n: number of free electrons
|e|: electron charge
𝜇e: electron mobility
what are the four things that increase metal resistivity?
Presence of imperfections, temperature, impurities, and cold working.
what is the difference between electrical properties of intrinsic and extrinsic semiconductors?
intrinsic: Same as pure material
Extrinsic: dictated by imparity atoms
What are the two types of electronic charge carriers?
a free electron (negative charge)
a hole (positive charge)
what is this formula 𝜎 =𝑛|𝑒|𝜇𝑒 + p|𝑒|𝜇h
𝜎 = conductivity
𝑛 = number of free electrons
𝑒 = electrical charge
𝜇𝑒 = electron mobility
p = number of holes
𝜇h = hole mobility
in an intrinsic semiconductor the number of electrons = ?
the number of holes
in an extrinsic semiconductor does the number of holes equal the amount of free electrons?
NO
does a p or a n type extrinsic semiconductor have more holes or free electrons?
n-type has more electrons!
in intrinsic semiconductors, does conductivity increase or decrease with temperature
increase
When impurity atoms are added to extrinsic semiconductors does the conductivity increase or decrease?
increase as imperfection sites lower the
activation energy to produce mobile electrons
what is the heat capacity
energy stored as atomic vibrations required to increase a mole of material by a unit T
what is the coefficient of thermal expansion? which material has the highest values?
the size of a material changes with a change in temperature
* polymers have the largest values
What is Thermal conductivity? Which material has the highest value?
the ability of a material to transport heat
* metals have the largest values
what is this formula? C = ∆Q / ∆T
C = Heat capacity
∆Q = change in energy (energy input)
∆T = change in temperature
what is the Debye temperature?
the temperature where energy is no longer stored as waves
what does this formula do (lf - li) / li = αl * (Tf - Ti)
lf = length final
li = length initial
al = thermal expansion
Tf = temperature final
Ti = temperature inital
what does this formula do q = -k ( ∆T / ∆x)
q = heat flux
∆T = change in temperature
∆x change in length
NOTE THAT ( ∆T / ∆x) is temperature gradient
