P8 Flashcards
What is electric charge
Physical property of matter measured in coulombs - can have none aka neutral or some aka charge carrier
what is the elementary charge
1.6 x10^-19 C
Why is charge described as quantised
As net charge = +- ne, charge can only have certain values as it must be an integer multiple of e (as number of electrons must be an integer)
What defines an electric current
Flow of any charge carriers, e.g ions, electrons
How does current flow in metals
Delocalised electrons move to positive end and repelled from negative, though collide with vibrating positive ions
Conventional current vs electron flow
Conventional current - direction of all electric currents (not just e-) treated as positive to negative, while electron flow itself is negative to positive
Where and what resistance should an ammeter be
Place in series anywhere with minimal resistance so to not affect current
How does conservation of charge link with Kirchoff’s first law
Electric charge cannot be created or destroyed - constant. Similarly the law states the sum of current into a point must = the sum out
Equation linking charge current time
Q = It
Equation linking voltage current resistance
V = IR
what is number density
number of free charge carriers per unit volume
electrons per metre cubed
number density and conductivity correlation
high number density = conductor - x10^28
medium number density = semiconductor - x10^17 ish
low number density = insulator
What is mean drift velocity
Free electrons repeatedly collide with +ive metal ions
But overall superimposition drifted towards positive terminal
Rate of e- movement usually slow but seems instantaneous as everything starts moving almost at once
Equation for mean drift velocity
I = anev
or v = I/ane
Derivation of I = anev
I = Q/T
total charge of all electrons in given volume = neV
I = neV/T
Volume of charge carriers per second - V/t = Av
So I = anev
Effect of changing CSA
Less CSA means more velocity - change in radius causes factor 2 change as r^2
