Electricity Definitions Flashcards
define: the coulomb
the charge that flows (past a point) in 1 second when the current is 1A
define: electric current
the charge that flows pasts a point in a circuit per unit time
define: conventional current
the direction in which positive ions/charges move OR the OPPOSITE direction to the electron flow
direction of conventional current
From positive to negative
direction of electron flow
From negative to positive (remember that electrons are negative) (opposite to conventional flow)
direction of electron flow within a cell
The electron flow continues in the same direction as the external circuit and so it flows from the positive terminal to the negative terminal (an exception to the norm)
what does Q=It stand for
charge=current x time. Charge is measures in coulombs (C). Current it measured in amps (A) and time in seconds (s).
what does I=nevA stand for
I=current n=number density e=elementary charge v=average drift velocity(of the electrons) A= cross sectional area
what does number density mean
the number of conduction electrons per unit volume (therefore measured in m^-3) for copper this value is 10^29
what does elementary charge mean
The charge on each electron. Is always 1.6 x 10^-19 C
define: Kirchhoff’s 1st law
sum of currents entering a junction = sum of currents leaving a junction. This law is an expression of the conservation of CHARGE
define: Kirchhoff’s 2nd law
For a CIRCUIT LOOP sum of e.m.f. s = sum p.d. s.
This law is an expression of the conservation of ENERGY
define: p.d.
Energy transferred from electrical energy to other forms per unit charge
define: e.m.f.
(essentially the opposite of p.d.) Energy transferred from other forms into electrical energy per unit charge
define: terminal p.d.
the potential difference across the terminals of a cell (N.B this may NOT be the same as the e.m.f. of the cell, due to internal resistance)
Define: internal resistance (of a chemical cell)
electrical resistance due to chemical processes within a cell i.e the resistance from an e.m.f. source
ohm’s law
the current is directly proportional to the p.d. (voltage) at a constant temperature
Define: the ohm
Is the resistance of a component when a potential difference of 1 volt is produced per amp
Ohmic
describes a component that obeys Ohm’s law
e.g a resistor
Non-ohmic
describes a component that does NOT obey Ohm’s law e.g. a filament bulb or a diode
define: electrical resistance
resistance = voltage/current
resistivity equation
ρ=RA/L where ρ=resistivity-measured in ohm metres R=resistance A=cross-sectional area L=length
define: kilowatt-hour
the energy transferred when a 1kW device operates for 1 hour
potential divider equation
V out = R2/ (R1+R2) x by V in
