Charge and current

Question 1

what is electrical current

Answer 1

the rate of flow of charge
can be any type of charge carrier not just electrons

Question 2

what is electrical current measured in

Answer 2

amperes

Question 3

what is the equation for electrical current

Answer 3

I=Q/t

Question 4

what is one ampere

Answer 4

one coulomb of charge passing a given point per second

Question 5

what is electrical charge

Answer 5

a physical property
a measure of chargedness e.g. some particles are charged like protons and electrons and others are not like neutrons

Question 6

what are the two types of charge

Answer 6

positive and negative

Question 7

how do the two types of charges interact

Answer 7

like charges repel
opposite charges attract

Question 8

what is electrical charge measured in

Answer 8

coulombs C

Question 9

what is one coulomb equivalent to

Answer 9

one ampere per second

Question 10

what is a particle with an electric charge

Answer 10

a charge carrier

Question 11

what is the elementary charge

Answer 11

1.6x10^-19
the charge on one proton (negative for the charge of one electron)

Question 12

what is the net charge

Answer 12

the charge on objects due to the ain or loss of electrons
electrons added - negatively charged
electrons removed - positive charge

Question 13

how do give the net charge of an object

Answer 13

Q=+-ne
Q is the net charge on the object in coulombs
n is the number of electrons
e is the elementary charge

Question 14

what is the charge of an object described as

Answer 14

being quantised

Question 15

why is the chare on an object described as being quantised

Answer 15

because charge can only have certain values
values must be integer multiples of e

Question 16

what do the charge carriers tend to be in liquids

Answer 16

ions

Question 17

what is the structure of metal

Answer 17

regular crystal structure/lattice of positive ions surrounded by an number of free electrons
positive ions are not free to move but vibrate around a fixed point - vibrate more as the temp of the metal increases

Question 18

how can you make electrons move in a metal wire

Answer 18

make one end of wire positive and the other end negative
electrons attracted towards the positive end
electrons will move through the wire as an electric current

Question 19

why might there be a larger current in a wire

Answer 19

a greater number of electrons moving past a given point each second e.g. a wire with a greater cross sectional area
the same number of electrons moving faster through the metal

Question 20

what is conventional current

Answer 20

a model used to describe electric current in a circuit - travels from positive to negative, the direction in which positive charge would travel

Question 21

what electric current do liquids carry

Answer 21

electrolytes - a flow of ions
molten ionic compounds or ionic solutions

Question 22

what do you use to measure electric current

Answer 22

ammeter
placed directly in series in the circuit at the point where you want to measure the current

Question 23

when an ammeter is placed in series what qualities should it have

Answer 23

the lowest possible resistance - to reduce the effect they have on the current, high resistance would decrease the current

Question 24

what is the conservation of charge

Answer 24

electric chare can neither be created or destroyed
total amount of electric charge in the universe is constant

Question 25

what is kirchhoffs first law

Answer 25

for any point in an electrical circuit the sum of current into that point is equal to the sum of currents out of that point sum if I in = sum of I out

Question 26

what is the number density

Answer 26

the number of free chare carriers per unit volume

Question 27

what does a higher number density mean

Answer 27

the greater number of free electrons per m^3 better electrical conductor

Question 28

what are the tree groups of materials according to their number denisty

Answer 28

conductors insulators semiconductors

Question 29

what are conductors

Answer 29

very high number density

Question 30

what are semiconductors

Answer 30

a material with a lower number density than a typical conductor

Question 31

what is an insulator

Answer 31

a material with a low number density

Question 32

how can a semiconductor carry the same current as a conductor

Answer 32

electrons in a semiconductor need to move much faster increases the temp of the semiconductor

Question 33

what is drift velocity

Answer 33

number of electrons passing a point in time will be given by the density of electrons multiplied by the volume taken up be these conduction electrons

Question 34

what is the equation for mean drift velocity

Answer 34

I=nAve I is the electric current in the conduction in amperes A is the cross sectional area of the conductor in m^2 e is the elementary charge n is the number density v is the mean drift velocity of the charge carriers is ms^-1

Question 35

how do you derive the equation of I=nAve

Answer 35

I=Q/t the number of electrons is given in volume V of the conductor is nV the total charge of the electrons in this volume of conductor is neV where e is the elementary charge give I=(neV)/t when there is an electric current in the conductor a certain volume of charge carries passes a given point each second. this volume depends on the cross sectional area A of the conductor and the mean drift velocity v of the chare carriers V/t=Av sub into previous equation I=nAve

Question 36

what effects the mean drift velocity of a metal

Answer 36

the cross sectional area

Question 37

how doe the cross sectional area affect the mean drift velocity

Answer 37

narrower the wire the greater the drift velocity in order for the current to be the same