Electricity

Question 1

a.c.

Answer 1

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

Question 2

Alternator

Answer 2

an a.c. generator.

Question 3

Capacitance`

Answer 3

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.

Question 4

Capacitor

Answer 4

two (or more) conductors separated by an insulator that can be used to store charge

Question 5

d.c.

Answer 5

direct current. The current from a d.c. supply always moves in the same direction around an electric circuit.

Question 6

Depletion layer

Answer 6

the area surrounding the p-n junction of a diode where the electrons have combined with the holes leaving no free charges

Question 7

the area surrounding the p-n junction of a diode where the electrons have combined with the holes leaving no free charges

Answer 7

a net flow of charged particles

Question 8

Electromotive force (emf)

Answer 8

the electromotive force of a source is the electrical potential energy that is given to each unit of charge that passes through the source

Question 9

Forward-biased

Answer 9

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

Question 10

Intrinsic semiconductors

Answer 10

semiconductor material with no impurities

Question 11

Junction voltage

Answer 11

the potential difference between the ends of the depletion layer inside a p-n junction diode

Question 12

Leakage current

Answer 12

the tiny current in a reverse-biased diode

Question 13

Load resistor

Answer 13

the resistor, or combination of resistors, that forms the external part of an electrical circuit

Question 14

Lost volts

Answer 14

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.

Question 15

N-type semiconductor

Answer 15

semiconductor material that has an excess of free electrons

Question 16

Ohm’s law

Answer 16

the current in a conductor at constant temperature is directly proportional to the potential difference across it

Question 17

Open circuit

Answer 17

a circuit in which the current is zero. In the circuit there is a gap or an infinite resistance.

Question 18

Photodiode

Answer 18

a type of p-n junction diode that responds to light intensity

Question 19

Photovoltaic mode

Answer 19

the mode of operation of a photodiode where it can supply power to a load. This is the basis of a solar cell.

Question 20

Potential difference

Answer 20

the potential difference between two points is a measure of the work done in moving one coulomb of charge between the two points

Question 21

Potential divider

Answer 21

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.

Question 22

P-type semiconductor

Answer 22

semiconductor material that has an excess of free holes

Question 23

Resistance

Answer 23

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.

Question 24

Reverse-biased

Answer 24

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

Question 25

short-circuit

Answer 25

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.

Question 26

Short-circuit current

Answer 26

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’).

Question 27

Terminal potential difference (t.p.d.)

Answer 27

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.

Question 28

Thermistor

Answer 28

a resistor in which the resistance depends on its temperature