Resistivity and Conductivity Flashcards
When length doubles, what happens to resistance?
It doubles.
When cross-sectional area doubles, what happens to conductance?
It doubles.
What sort of properties are resistance and conductance?
Extensive.
What do extensive properties depend on?
- Length.
- Cross-sectional area.
- Material.
Resistance is proportional to…, so it is inversely proportional to…
Length. R=L
Cross sectional area. R = 1/A
Conductance is proportional to…. and inversely proportional to….
Cross sectional area. G = A
Length. G= 1/L
Metals have a high c…..e and a low r……e.
Conductance, resistance.
For the formulae of resistance and conductance, what constant is needed?
A bulk constant - an intensive property which depends on the materials.
What is the formula for resistance using resistivity?
R = pL/A (p = pho - ohms m )
What is the formula for conductance using conductivity?
G = ōA/L (ō is signal, S m^-1 )
To measure the conductivity, an experiment is needed. G = ōA/L. Therefore, the length, area, voltage, and current all need to be measured. How could uncertainty/systematic error arise, how could it be reduced, and what effect would this have?
Errors:
- Uncertainty in measuring thickness/height/width.
- Systematic error in the temperature which affects resistance.
- Resolution in the voltmeter or ammeter.
- Uncertainty in the resistance calculated.
Reduce:
- Use a micrometer to measure thickness.
- Use a vernier calliper to measure height/width.
- Maintain constant temperature.
- Repeat the measurements to ensure that the sensitivity is constant and reliable.
- Calculate averages for the resistance.
Effect :
- Reduces % uncertainty in results.
- More precision +- 1mm for the height/width or +-0.1mm for the thickness.
- Resistance is not affected by external factors - more repeatable.
How does resistance work in a circuit?
Forwards push of charges is balanced by obstructing effect of atoms in conductor.
What is resistance also considered to be?
Volts needed for one ampere. VA^-1
What is conductance also considered to be?
Amperes needed per volt AV^-1
What’s Ohm’s Law?
Resistance is constant for materials at constant temperature. voltage increases proportional to current.
