Chapter 25 Flashcards
Current, Resistance and Voltage
Drift velocity equation
Vd = (qETau) / m
2 key assumptions with drude model
- electron motion after collision is independent of motion before collision (random post-collision)
- Excess energy aquired by electrons in E is transferred to the lattice/ the positive nuclei in the conductor
Current eq
I = dQ/dt I = nqA (Vdrift) (derive from introducing "n")
n
Charges per unit volume
Current density J , a vector
J = I / A J = nq (Vdrift)
J direction relative
J // E // Vdrift
Resistivity (1/σ)
ρ = E / J
sub in to get:
ρ = m / (nq^2Tau)
Resistance eq
R = V/R
sub in to get:
R = (ρL) / A (via V and J subbing in)
What does resistance depend on?
R = (ρL) / A
- size
- shape
- properties of material (rho)
conventional current urrent definition
- the flow of positive charge carriers
- flows in the direction of E
Electric current I
the rate at which charge crosses a surface defines the current through that surface
What does J depend on
How much E you apply to the conductor
Ohmic material
Resistance remains constant at a fixed temperature
Electromotive force definition
The WORK done per unit charge (by the battery)
The potential difference across the battery
*emf is not actually a force or a V its just = to them
EMF for a real battery
Va = Emf - Ir
