08 Charge and Current

Question 1

electric current

Answer 1

the rate of flow of charge, measured in amps. Normally a flow of electrons in metals or of ions in electrolytes

Question 2

amperes

Answer 2

the base SI unit of electric current, defined as the current flowing in two parallel wires in a vacuum 1m apart such that there is an attractive force of 2.0x10^-7 N per metre length of wire between them

Question 3

positive (charge)

Answer 3

a type of electric charge - positively charged objects attract negatively charged ones and repel other positive charges

Question 4

negative (charge)

Answer 4

a type of electric charge: negatively charged objects attract positively charged ones, and repel other negative charges

Question 5

coulombs

Answer 5

the derived SI unit of electrical charge, 1 C of electric charge passes a point in 1s when there is an electric current of 1A (1C = 1As)

Question 6

electric charge

Answer 6

a physical property, either positive or negative, measured in coulombs, or as a relative charge

Question 7

ions

Answer 7

atoms that have either lost or gained electrons and so have a net charge

Question 8

relative charge

Answer 8

simplified measurement of the electric charge of a particle or object, measured as multiples of the elementary charge

Question 9

elementary charge

Answer 9

the electric charge equivalent to the charge on a proton

Question 10

free electrons

Answer 10

electrons in a metal that are not bound to an atom and are free to move - sometimes called delocalised electrons

Question 11

conventional current

Answer 11

current that flows from the positive terminal of a cell to the negative terminal

Question 12

electrolytes

Answer 12

liquids containing ions that are free to move and so to conduct electricity

Question 13

ionic solutions

Answer 13

an ionic compound dissolved in a liquid to form an electrolyte

Question 14

anions

Answer 14

negatively charged ions, ones which are attracted to an anode

Question 15

cations

Answer 15

positively charged ions, ones which are attracted to a cathode

Question 16

anode

Answer 16

a positively charged electrode

Question 17

cathode

Answer 17

a negatively charged electrode

Question 18

resistance

Answer 18

potential difference across a component divided by the current through it

Question 19

conservation of charge

Answer 19

law which states electric charge can be neither created nor destroyed - total charge in any interaction must be the same before and after the interaction

Question 20

Kirchhoff’s first law

Answer 20

total currents into a junction equals the total current out

Question 21

semiconductor

Answer 21

a material with a lower number density than a typical conductor, eg silicon

Question 22

mean drift velocity (of electrons in a wire)

Answer 22

average displacement travelled of the electrons along a wire per second (1/3 marks) where they move slowly in one direction through the metal lattice (2/3) and collide constantly with the lattice (3/3)

Question 23

value of n: conductors, semiconductors, insulators

Answer 23

conductors: very large
semiconductors: in between
insulators: close to zero

Question 24

quantised

Answer 24

describes a quality such as energy or charge that is only available in certain discrete values