Circuit Laws And Resistivity Flashcards
(17 cards)
What’s the formula for resistivity?
R= pL/A
What are the units for resistivity?
Ohm m
How will increasing the length of a wire affect its potential difference?
For a given current or rate of flow of electrons, increasing the length will increase the potential difference across it as the electrons will have to do more work to travel the increased length
How will increasing the CSA of wire affect the resistance?
When the CSA of wire increases, resistance decreases
for a given pd, doubling the CSA will double current or rate of flow of electrons.
What’s the relationship between resistance a length of a wire?
R is directly proportional to L
What’s the relationship between resistance and CSA of a wire?
R is inversely proportional to CSA
What are the formulas for total current, voltage & resistance in a series circuit?
I = I1 = I2 = I3
V = V1 + V2 + V3
R = R1 + R2 + R3
What are the formulas for total current, voltage & resistance in a parallel circuit?
I = I1 + I2 + I3
V = V1 = V2 = V3
1/R = 1/R1 + 1/R2 + 1/R3
State kirchoff’s first law
The total current entering a junction = the total current leaving it
What is conserved in kirchoff’s 1st?
Charge
State kirchoff’s second law
The total EMF around a series circuit is equal to the sum of the potential differences across each component
What is conserved in kirchoff’s second law?
Energy
Define election number density, include unit
The number of free electrons per unit volume in m^-3
How is electron number density related to the material’s resistivity & conductivity?
The greater the n of a material, the lower the material’s resistivity & the greater the material’s conductivity
how does temp affect resistivity in a metal wire and why?
as temp increases, so does resisitivity, this is because higher temperatures cause greater vibrations of the metal ions meaning its harder for current to pass through, so resistance and resistivity both increase
define a semiconductor
a material that has a conductivity between that of conductors and insulators
how does temp affect resistivity in a semiconductor?
as temp increases, resistivity decreases because at higher temps more conduction electrons become available, this means greater current can flow for a given potential difference so resistance and resistivity both decrease
