Electricity Flashcards
a.c.
alternating current. The current from an a.c. supply constantly changes direction.
Alternator
an a.c. generator.
Capacitance`
the ratio of electric charge to potential difference between any two conductors separated by an insulating material. The capacitance of a system of conductors describes the ability of the system to store electric charge.
Capacitor
two (or more) conductors separated by an insulator that can be used to store charge
d.c.
direct current. The current from a d.c. supply always moves in the same direction around an electric circuit.
Depletion layer
the area surrounding the p-n junction of a diode where the electrons have combined with the holes leaving no free charges
the area surrounding the p-n junction of a diode where the electrons have combined with the holes leaving no free charges
a net flow of charged particles
Electromotive force (emf)
the electromotive force of a source is the electrical potential energy that is given to each unit of charge that passes through the source
Forward-biased
a diode connected in a circuit such that the p-type terminal is more positive than the n-type terminal
Intrinsic semiconductors
semiconductor material with no impurities
Junction voltage
the potential difference between the ends of the depletion layer inside a p-n junction diode
Leakage current
the tiny current in a reverse-biased diode
Load resistor
the resistor, or combination of resistors, that forms the external part of an electrical circuit
Lost volts
the potential difference that is used to drive a current through the internal resistance of a source. Lost volts is given by the expression Ir where r is the internal resistance of the source.
N-type semiconductor
semiconductor material that has an excess of free electrons
Ohm’s law
the current in a conductor at constant temperature is directly proportional to the potential difference across it
Open circuit
a circuit in which the current is zero. In the circuit there is a gap or an infinite resistance.
Photodiode
a type of p-n junction diode that responds to light intensity
Photovoltaic mode
the mode of operation of a photodiode where it can supply power to a load. This is the basis of a solar cell.
Potential difference
the potential difference between two points is a measure of the work done in moving one coulomb of charge between the two points
Potential divider
a circuit consisting of a number of resistors (often only two) in series, connected across a supply, that is used as a source of fixed or of variable p.d.
P-type semiconductor
semiconductor material that has an excess of free holes
Resistance
the opposition that a conductor offers to a current through it. Defined as the ratio of potential difference across the conductor to the current through it.
Reverse-biased
a diode connected in a circuit such that the p-type terminal is more negative than the n-type terminal
short-circuit
a circuit in which the current is at its maximum. In this type of circuit the resistance connected across the terminals of the source is 0 Ω. The only resistance in the circuit will be the internal resistance, r.
Short-circuit current
the maximum current that a source can supply. The current drawn from the supply when there is zero resistance in the external circuit (when the terminals of the source are joined together or ‘short-circuited’).
Terminal potential difference (t.p.d.)
the terminal potential difference is the potential difference that appears across the terminals of a source when the source is supplying a current to a circuit. It is the potential difference that appears across the external resistance, or load resistor, in the circuit.
Thermistor
a resistor in which the resistance depends on its temperature
