electricity

Question 1

property of matter that causes electric field

Answer 1

charge

Question 2

charge scalar or vector

Answer 2

scalar

Question 3

value of fundamental charge

Answer 3

1.6x10^-19

Question 4

what is fundamental charge

Answer 4

smallest amount of charge that exists in ordinary matter - protons and electrons have this same charge but with opposite sign

Question 5

electric field

Answer 5

region of space where an electric force is experienced

Question 6

field strength (E)

Answer 6

the force experienced by a small + charge placed at a point in the field

Question 7

potential of a sphere

Answer 7

the amount of work done per unit charge to bring a small positive charge from infinity to the surface of the sphere

Question 8

units of potential

Answer 8

JC^-1 (same as volt)

Question 9

coulomb’s law

Answer 9

The force experienced by two point charges is directly proportional to the product of their charge and inversely proportional to the square of their separation

Question 10

law for the force between masses in a) an electric field and b) a gravitational field

Answer 10

a) Coulomb’s law

b) Newton’s law

Question 11

what makes smth a good conductor

Answer 11

allows a large current for a given pd

Question 12

ohm’s law

Answer 12

the current through an ohmic conductor is directly proportional to the pd across it provided that the temperature remains constant

Question 13

why does temperature affect resistance

Answer 13

because an increase in temperature means increased lattice vibrations resulting in more collisions between electrons and the lattice

Question 14

why does increasing the temperature of a semiconductor lead to lower resistance

Answer 14

liberates more electrons

Question 15

primary cell

Answer 15

cell that cannot be recharged

Question 16

emf of a cell layman’s and IB

Answer 16

• the energy provided by a cell or battery per coulomb of charge passing through
• the work done taking unit charge from one terminal to the other (low potential to high potential)

Question 17

how many kg in a tonne

Answer 17

1000

Question 18

electric potential energy for a sphere of charge

Answer 18

V =Qk/r^2

Question 19

how many electrons per second to produce 1 amp of current?

Answer 19

6.2x10^18

Question 20

internal resistance

Answer 20

the resistance of the components inside a battery.

Question 21

terminal potential difference what is it and relationship to emf

Answer 21

pd across the terminals of the battery

equal to emf, but if a current flows it will be less than emf

Question 22

what does emf stand for

Answer 22

electromotive force

Question 23

electrical power

Answer 23

the rate at which energy is changed from one form to another

Question 24

kirchhoff’s first law

Answer 24

current into junction = current out of junction

Question 25

kirchhoff's second law

Answer 25

around any closed circuit, the sum of the emfs = the sum of the pds

Question 26

ohm's law equation

Answer 26

V = IR

Question 27

ideal ammeter vs ideal voltmeter

Answer 27

Ideal voltmeter has infinite resistance | Ideal ammeter has zero resistance.

Question 28

field strength unit

Answer 28

NC^-1

Question 29

EPE (electric potential energy) equation

Answer 29

EPE = Vq

Question 30

conventional current flow vs electron flow

Answer 30

conventional current moves from high to low potential (ie +ve to -ve) however electrons flow the other way as attracted to +ve

Question 31

convert joules to electron volt (eV)

Answer 31

divide by fundamental charge

Question 32

what is an electronvolt

Answer 32

energy gained by an electron accelerated through a pd of 1V

Question 33

emf

Answer 33

energy converted from chemical to electrical per unit charge

Question 34

electrical power

Answer 34

the rate at which energy is changed from one form to another

Question 35

power delivered in a perfect battery

Answer 35

energy converted from chemical to electrical per unit time

Question 36

power dissipated in resistor

Answer 36

amount of electrical energy converted to heat per unit time

Question 37

electric kettle

Answer 37

transfers the heat produced when current flows through a wire element to the water inside the kettle

Question 38

magnetic flux density (B)

Answer 38

quantity used to measure how string magnetic field is

Question 39

definition of ampere

Answer 39

one ampere is defined as the current that would cause a force of 2x10^-7N/m between two long parallel conductors separated by 1m in a vacuum

Question 40

what does it mean if a lamp is labelled '3 volts, 0.6 watts'

Answer 40

This means that if the bulb is connected to 3V then 0.6W of power is dissipated

Question 41

electric cell

Answer 41

device that uses the energy stored in chemicals to arrange charges in such a way that a p.d. is created which can be used to cause a current to flow in a conductor

Question 42

how is chemical energy = electrical PE

Answer 42

chemical energy = energy associated with molecules | molecules = charged bodies arranged in such a way that they don't fly apart

Question 43

when is the pd across r (internal resistance) equal to the EMF

Answer 43

when resistance R of external circuit = 0

Question 44

when is the pd across the terminals of the cell equal to the emf?

Answer 44

``` When I is zero there will be no pd across r (internal resistance) , so V = E ```

Question 45

pd across a resistor

Answer 45

amount of electrical energy converted to heat per unit charge so if energy is conserved

Question 46

why might resistance be greater if power dissipated in the resistor is greater than recommended maximum

Answer 46

``` When current passes through the resistor heat is dissipated causing the temperature of the resistor to increase. Increased temperature will increase the resistance. ```

Question 47

the equation for k when you have a situation with charges not in a vacuum,

Answer 47

k= 1/4πε

Question 48

direction of movement of POSITIVE charge

Answer 48

Positive charge will always move from high to low potential

Question 49

resistivity

Answer 49

the resistance of 1 m3 of substance.

Question 50

why does the ideal voltmeter have high resistance

Answer 50

so it doesn't draw any current

Question 51

magnetic field lines direction

Answer 51

always north to south

Question 52

state, in terms of electrons, the difference between a conductor and an insulator

Answer 52

a conductor contains 'free' electrons and insulators do | not

Question 53

resistance mark scheme definition

Answer 53

the ratio of potential difference across a device/load/resistor to current in the device/load/resistor

Question 54

difference in thermal capacity gas heated at constant pressure vs gas heated at constant volume

Answer 54

the thermal capacity for gases at constant volume is less, because all the thermal energy supplied goes to increasing the internal energy, so the increase in temperature in the constant volume case is greater

Question 55

why must there be an electric field inside a conductor

Answer 55

Because in order to have a current, electrons must be moving along the wire -> so a force (electric force) must be acting on them

Question 56

what is the force on a free electron inside a conductor

Answer 56

electric field strength x elementary charge

Question 57

whats a test charge

Answer 57

point charge which has no effect on the field in which it is placed

Question 58

what do electric cells do

Answer 58

convert chemical energy into electrical potential energy

Question 59

what is a magnetic field

Answer 59

a region of space where a small magnetic dipole experiences a turning force

Question 60

why are magnetic poles called north-seeking and south-seeking

Answer 60

because they point in those directions if suspended

Question 61

unit of magnetic flux density (B)

Answer 61

tesla(T)

Question 62

charge x voltage

Answer 62

energy