What is the electrical conductivity?
The mobility of conducters times amount of conducters times the amount of transferred charge.
How can the resistivity be calculated from the conductivity?
How can the electrical field be calculated from the resistivity?
How can the elect. resistance be calculated from the resistivity?
Give Ohms law.
U=RI <=> J=(sigma)*E
sigma stands for the conductivity
How can the resistivity be calculated using the average collision time?
Which components add to the resitivity in metals?
How is the change in resistivity with temperature calculated?
How is the resisitvity of impurities calculated?
What is the influence of the deformation of on the resistivity?
Deformed copper has 98% of the conductivity of undeformed copper.
What is the Franz-Wiedmann Law?
The relation between the thermal and electrical conductivity:
Which atomic bodies beside electrons can contribute to the conductivity?
Ions (eg. in Ceramics)
What are the best conductors?
Superconducters with no resistivity
Tc for the transition to superconductivity
How can the conductivity of polymers be increased?
addition of filler materials (eg. graphite)
How can conductivity in polymers be calculated?
Name 5 intrinsically conductive polymers.
Poly(p-pentylene
polyacetylene
polypyrole
polythiophene
polyaniline
How can the condcutivity of the intrinsically conductive polymers be reversibly controlled?
Doping with electrically active impurities.
How can the electrical properties in this bar be calculated?
What is the four point technique and how can the resitiivity of it be calculated?
What are the main errors in resistivity measurement?
unclean contacts
surface layer
ageing of contacts
applied volatage can cause heating
(voltmeter input resistance higher than 10^5)
ohms law not always obeyed
What describes the dielectric constant?
The polarisability of a material <=> the permitivity of electric force lines
Which materials have generally speaking which dieelectric constant?
low: vacuum, dry air, helium
medium: distilled water, glass, ceramics
high: metal oxides
How is the dipol moment defined?
How is Polarization defined?
µ=dipole moment
How is capacity calculated? How is capacity calculated for a plate condenser?
How is the susceptibility defined?
The ability to polarize under an external Electric field.
For condensators:
What are linear dielectrics?
Materials with a linear relation between polarization and applied electric field.
What are non linear dielectric materials? What are the subcatigories?
Materials with a spontainous polarization in the absence of a field
piezoelctrics
pyroelectrics
ferroelectrics
What is piezoelctrism?
Change in polarisation <=> increase in voltage due to a applied deformation
What is pyroelectrims?
Change in polarisation <=> increase in voltage due to temperature change
needs to be piezoelectric
What is ferroelectrism?
Change in polarisation <=> change in voltage due to applied voltage
needs to be piezoelectric and pyroelectric
On what depends the dielectric strength of a material?
specimen thickness
electrode shape
rate of applied voltage change
medium sourrounding the sample
What is understood under a dielelectric breakdown?
if Voltage/E-field becomes too great material will begin to conduct current
Name some everyday examples of dielectric breakdown.
Lightning
plasma TV
How is the current composed in an alternating dielectric effected circuit?
c=charging current
l=loss current
How is can the current be calculated in an alternating dielectric effected circuit?
How does one come from the first to the second equation?
How is the angle of the complex dieelectric vector calculated?
D=dissipation factor (dielectric loss)
How is the conductance in a variable load conuctor calculated?
How is the work loss calculated?
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