Even more higher physics electricity

Intrinsic semiconductor

Undoped group 4 semiconductor eg Silicon

Extrinsic semiconductor

A semiconducting group 4 material with impurities of group 3 or group 5 material

Doping

When very small amounts of impurities are added to the intrinsic semiconductor, this changes the properties of the material.

Diode

A component made of n-type and p-type material grown together to create (a device that allows current in one direction only)

junction

Where the n-type and p-type materials are joined, this allows electrons and holes to diffuse across the gap

Conductor

A solid material that has electrons in the conduction band

Insulator

A solid material with no electrons in the conduction band and a large energy gap between the valence and conduction bands

Valence band

The highest occupied band containing electrons. The band containing electrons with the highest energies and still be associated with a particular atom of a solid material.

Conduction band

The first unfilled band above the valence band, allowing the electron to dissociate from a particular atom and become a free charge carrier in the material.

a.c.

alternating current. The current from an a.c. supply constantly changes direction.

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

electric current

a net flow of charged particles

electromotive force

the electromotive force of a source is the electrical potential energy that is given to each unit of charge that passes through the source. For example an EMF of 1.5 V means 1.5 J of energy is supplied to each C of charge.

excited state

any atomic energy level higher than the ground state

Forward-biased

a diode connected in a circuit such that the p-type terminal is more positive than the n-type terminal

Frequency

the number of complete cycles of a wave passing a given point in a given time, usually per second. Frequency is measured in hertz (Hz) where 1 Hz = 1 wave per second.

fundamental unit of charge

e; the magnitude of charge carried by one electron or one proton. Equal to 1.60 x 10-19 coulombs.

ground state

the lowest energy level of an atom

Instantaneous

at one point in time or at one particular instant in time

internal resistance

the opposition to current in a source of electrical energy

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.

Monochromatic

one energy, one frequency, one wavelength, one colour

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.

Period

the time to make one complete wave. Period is measured in seconds.

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 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

wheatstone bridge circuit

a resistor network, consisting of a series/parallel combination that can be used to measure resistance when balanced. In the out-of-balance condition, a small p.d. that is proportional to the change in resistance is produced

valence shell

the atomic energy level that contains the outermost electrons of the atom. It is the electrons in this shell that determine the chemical reactions between elements.