Electricity - Definitions

Question 1

Direct Current (D.C)

Answer 1

When current flows in only one direction at all time

e.g. A battery

Question 2

Alternating Current ( A.C)

Answer 2

When current changes direction every fraction of a second

E.g. The mains is a A.C source

Question 3

Electromotive force (EMF)

Answer 3

The Maximum energy given to each coulomb of charge that passes through the cell when no current is flowing.

Question 4

tpd ( terminal potential difference)

Answer 4

This is the voltage measured across a battery (or cell) when it is doing work i.e. a current is flowing

Question 5

Lost volts

Answer 5

the energy “ lost” per coulomb (voltage) as the current passes through the battery (or cell). (Lost volts cause a battery to heat up when it is working too hard.)

Question 6

Capacitance

Answer 6

The capacitance of a capacitor is a measure of the amount of charge it can store for every volt across it.

Question 7

Conductor

Answer 7

A material which has many free electrons ( all metals,graphite)

Question 8

Insulator

Answer 8

A material which has very few free electrons ( plastic,glass,wood)

Question 9

SemiConductor

Answer 9

Very few free electrons when pure but can conduct when impurities are present and under certain conditions. (Silicon, germanium)

Question 10

Explain conductors in terms of the band gap theory

Answer 10

For metals we have the situation where one or more bands are partially filled.
Some metals have free electrons and partially filled valence bands, therefore they are highly conductive.
Some metals have overlapping valence and conduction bands. Each band is partially filled and therefore are conductive.

Question 11

Explain pure semiconductors in terms of the Band Gap theory

Answer 11

In a semiconductor, the gap between the valence band and conduction band is smaller and at room temperature there is sufficient energy available to move some electrons from the valence band into the conduction band allowing some conduction to take place. An increase in temperature increased the conductivity of a semiconductor.

Question 12

Explain insulators in terms of the Band Gap theory

Answer 12

In an insulator, the highest occupied band (called the valence band) is full. The first unfilled band above the valence band is the conduction band. For an insulator, the gap between the valence band an the conduction band is large and at room temperature there is not enough energy available to move electrons from the valence band into the conduction band where they would be able to contribute to conduction. There is no electrical conduction in an insulator.

Question 13

Doping

Answer 13

Adding an impurity to make an extrinsic semiconductor

basically adding an impurity to make it less resistant

Question 14

N-type semiconductor

Answer 14

The semiconductor is overall neutral.

The conduction happens through negatively charged electrons

Question 15

P-type semiconductor

Answer 15

Overall neutral

The majority charge carriers are positively charged holes.