Electricity Flashcards
(38 cards)
Electric current
Rate of flow of charge
The elementary charge
e = 1.6 x 10^-19 C
The net charge on a particle or an object is
Quantised and a multiple of e
Current
The movement of electrons in metal and movement of ions in electrolytes
Current (I) =
Charge (Q) / time (t)
Conventional current flows from
Positive to negative
Kirchhoff’ a first law
At any junction in a circuit the sum of the currents entering is equal to the sum of currents leaving - the conservation of charge
In series, the current
Is the same
In parallel, the current
Splits between branches
Mean drift velocity
The average displacement per unit time of charge carrier
Mean drift velocity equation
I = Anev
Typical n value for metal
10^28 m-3
N
Number density of charge carriers
Potential difference
The work done per unit charge by charge carriers as they move from one point to another in a circuit, transferring electrical energy to other forms
EMF and P.d. Units
JC^-1 or V
EMF/P.d. =
Work (j) / Charge (C)
Difference between EMF and P.d
EMF is work done by a battery, P.d is the work done by charge carriers
Kirchhoff second law
Around any loop in a circuit the sum of the EMFs is equal to the sum of the p.ds - conservation of energy
Work done (energy transferred) =
V x Q
EMF x Q
Energy transferred (eV) =
1/2 x mv^2
Resistance unit
Ohm
Resistance equation
R=V/I
Resistance
The potential difference per unit current
Ohms law
Potential difference is proportional to current for an ohmic conductor at constant temperature
