8. Charge and Current (4.1) Flashcards
What was the Milikan Experiment?
| just a brief overview
- charged oil drops poured into a uniform electric field between plates separated by distance (d) with p.d (V)
- aim of experiment was to determine charge of each oil drop
Q = (mgd)/V
What is the conductive band?
The energy level of electrons in which they have enough energy to escape the atom/ion and carry the charge
Conductive band in conductors vs Semiconductiors:
Conductors:
- conductive band is almost full thus valence electrons can easily + readily carry charge
Semiconductors:
- conductive band is almost empty, electrons barely available to carry charge
What two things constitute a higher current?
- electrons moving faster
- more electrons moving past a point per second
What is Kirchoff’s first law?
For any point in a circuit, the sum of the current into that point is equal to the sum of the current out of that point.
Σin = Σout
What is number density?
The number of free charge carriers per unit volume (usually in electrons per m^3)
What does a higher number density indicate?
That the material is a better conductor
Equation for current using number density:
I=Anev or I=AnQv
I = current (A)
A = cross-section area (m^2)
n = number density (m^3)
e = elementary charge (C) Q = charge of 1 charge carrier (C)
v = mean drift velocity (ms^-1)
What is the unit of charge?
The coulomb
How many coulombs is the elementary charge?
1.6 x 10^-19
In metals, what carries charge?
Electrons
In electrolytes, what carries current?
Ions
Is charge continuous or quantised?
Quantised
What is the direction of conventional current?
Positive to negative
What is the direction of electron flow?
Negative to positive
arrange conductors, insulators, semiconductors in order of increasing number density:
- insulators
- semiconductors
- conductors
