P2 ELECTRICITY

Question 1

what can be said about the value of current at any point in a single closed loop?

Answer 1

current is the same at all points in a closed loops

Question 2

2 factors that current in a circuit depend on?

Answer 2

potential difference
resistance

Question 3

define electrical current

Answer 3

the rate of flow of electrical charge

Question 4

define an ohmic conductor?

Answer 4

a conductor where resistance remains constant as the current changes.

Question 5

name four non-ohmic conductors?

Answer 5

lamps , diodes , thermistor , LDRs

Question 6

name two ohmic conductors?

Answer 6

wires , fixed , resistors

Question 7

describe how the resistance of a filament lamp changes with temperature?

Answer 7

as temperature increases , the resistance increases.
ions in metals have more energy , so vibrate more often causing more collisons with electrons as they flow through the metal , creating greater resistance to current flow

Question 8

describe how a diode conducts electricity

Answer 8

it only conducts electricity in one direction as it has a very high pressure in the backwards direction

Question 9

describe how the resistance of a thermistor changes with temperature ?

Answer 9

as temperature increases , the resistance decreases.

Question 10

describe a use of thermistors

Answer 10

thermistors can be used in thermostat circuits to automatically turn the heating on when it gets too cold , or switch it off when its gets hot

Question 11

describe how the resistance of an LDR changes with light intensity

Answer 11

as light intensity increases , the resistances decreases.

Question 12

describe a use of LDRs

Answer 12

can be used in automatic lights , to turn on automatically when it gets dark ,and switch off automatically when it gets light

Question 13

which two things are needed for charge to flow through a circuit

Answer 13

the circuit must be closed and there must be a source of potential difference

Question 14

state the rule for current in a series circuit?

Answer 14

the current will be the same at all points in a series circuit.

Question 15

if the resistance of a component increases , what will happen to the current through that component?

Answer 15

it will decrease

Question 16

unit for potential difference

Answer 16

Volts (V)

Question 17

units for resistance

Answer 17

Ohms (Ω)

Question 18

describe how current is measured

Answer 18

with an ammeter connected in series

Question 19

describe how voltage is measured

Answer 19

with a voltmeter connected in parallel to the component you want to measure

Question 20

what are the two ways that a component can be connected in a circuit ?

Answer 20

series (same loop)
parallel (adjacent loop)

Question 21

give the rule for current in series current

Answer 21

the current is the same at all points in a series current

Question 22

give the rule for current in parallel current

Answer 22

the current in a parallel circuit is shared between the branches of the circuit .

Question 23

give the rule for resistance in a parallel circuit

Answer 23

when resistors are connected in parallel , the total resistance is less than the resistance of the smallest resistor.

Question 24

give the rule for resistance in a series circuit

Answer 24

the total resistance in a series circuit is the sum of all the individuals resistances

Question 25

give the rule for potential difference in a series circuit

Answer 25

potential difference is shared between the components in a series current

Question 26

give the rule for potential difference in a parallel circuit

Answer 26

potential difference is the same in each branch of a parallel circuit

Question 27

describe a series circuit

Answer 27

a circuit where all components are connected in one single loops

Question 28

describe a parallel circuit

Answer 28

a circuit where there are multiple paths and current could take

Question 29

describe the current in series circuit

Answer 29

the current is the same at all positions since the charge only has one path to flow through

Question 30

describe the current in series circuit

Answer 30

the current is shared between the different branches . when the charge reaches a junction it splits

Question 31

why is it advantageous to connect lamp in parallel

Answer 31

if one lamp blows the rest will be unaffected and can still receive current

Question 32

is mains electricity an a.c supply or d.c supply? what do these stand for?

Answer 32

mains electricty is an a.c supply a.c = alternating current d.c = direct current

Question 33

what is alternating current?

Answer 33

current that continously changes direction at a specific frequency.

Question 34

what is direct current?

Answer 34

one directional current flow

Question 35

what is the frequency and voltage of the UK mains electricity supply?

Answer 35

frequency = 50hz voltage = 230v

Question 36

how many wires are usually in the cables connecting electrical appliances to the main? name these wires

Answer 36

live wire neutral wire earth wire

Question 37

state the insulation colour used on the earth wire

Answer 37

green and yellow

Question 38

state the insulation colour used on the live wire

Answer 38

brown

Question 39

state the insulation colour uses on the neutral wire

Answer 39

blue

Question 40

explain when the earth wire does and doesn't carry a current

Answer 40

if there is a fault current will flow to the ground. under normal circumstances no current flows through the earth wire

Question 41

what potential is the neutral wire at

Answer 41

0 volts

Question 42

state the potential difference between the live wire and earth wires

Answer 42

230 volts

Question 43

purpose of neutral wire?

Answer 43

to complete the circuit by connecting main appliances back to the main supply

Question 44

for metal appliances where is the earth wire connected to?

Answer 44

earth wire is connected to the metal casing of the appliance. if live wire becomes loose and touches the casing, the current will flow through the earth wire , preventing electrocution

Question 45

what 2 main factors does the amount of energy transferred by an appliance depend on?

Answer 45

how long the appliance is being used for. the power of the appliance

Question 46

describe the energy transfers in a battery powered torch?

Answer 46

The battery converts chemical energy into electrical energy. bulb converts electrical energy into light as well as waste energy in the form of heating

Question 47

describe the energy transfer in a battery powered motor?

Answer 47

battery converts chemical energy into electrical energy. motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction

Question 48

3 things that determine the power of the circuit?

Answer 48

the p.d across the circuit. current given through the circuit amount of energy transferred in a given time

Question 49

purpose of national grid?

Answer 49

to link power stations to consumers so that they have access to a source of electricity

Question 50

two types of transformers in national grid?

Answer 50

step up step down

Question 51

where are step up transformers found? and what do they do?

Answer 51

used when connecting power stations to transmission cables. increase potential difference

Question 52

where are step up transformers found? and what do they do?

Answer 52

used when connecting power stations to transmission cables. increase potential difference

Question 53

where are step down transformers found? and what do they do?

Answer 53

used connecting transmission cables to domestic buildings decrease potential difference

Question 54

why do transmission lines transfer electricity at high potentials?

Answer 54

high potential , results in a low current lower the current the less energy is wasted that is wasted as heat therefore is more efficient

Question 55

why do transmission lines transfer electricity at high potentials?

Answer 55

high potential , results in a low current lower the current the less energy is wasted that is wasted as heat therefore is more efficient

Question 56

why does the potential need to be decreased between transmission lines and houses

Answer 56

lower potentials are safer for domestic use and reduce the likelihood of severe electrocution appliances are designed for 230v