electricity

Question 1

what is electric current

Answer 1

the flow of electrical charge

Question 2

state the equation linking charge, current and time

Answer 2

Q = it

Question 3

state the units for charge for Q=IT

Answer 3

charge
current
time

Question 4

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

Answer 4

current is the same at all points in a closed loop

Question 5

what 2 factors does the current in a circuit depend on

Answer 5

1. potential difference
2. resistance

Question 6

what is an ohmic conductor

Answer 6

a conductor for which current and potential difference are directly proportional
resistance remains constant as current changes

Question 7

what is a condition required for a ohmic conductor

Answer 7

temp must be constant

Question 8

list 4 components for which resistance is not constant as current changes

Answer 8

1. lamps
2. diodes
3. thermistors
4. light dependent resistors

Question 9

what happens to the resistance of a filament lamp as temp increases

Answer 9

resistance increases
ions in metal have more energy so vibrate more causing more collisions with electrons as they flow through metal creating greater resistance to current flow

Question 10

what is different about current flow through a diode

Answer 10

the current only flows in one direction
resistance is very high in the other direction, preventing current flow

Question 11

state what happens to the resistance of a thermistor as temp increases

Answer 11

the thermistors resistance decreases

Question 12

give 2 examples of when a thermistor may be used

Answer 12

1. in a thermostat to turn a heater on below a certain temp
2. in a freezer to turn on a cooler when the temp becomes to high

Question 13

state what happens to the resistance of a LDR as light intensity increases

Answer 13

the LDR’s resistance increases

Question 14

give an application for a LDR

Answer 14

street lights often use LDR’s
when light levels become too low, the light gains sufficient current to turn on

Question 15

what are the 2 ways that a component can be connected in a circuit

Answer 15

1. series
2. parallel

Question 16

how does the potential difference across components vary when connected in series and parallel

Answer 16

series: total P.D is shared between each component
parallel: P.D across each component is the same

Question 17

if 2 resistors are connected in parallel, what can be said about their combined total resistance

Answer 17

their total resistance is less than the smallest of the two individuals

Question 18

if 2 resistors are connected in series, what can be said about their total resistance

Answer 18

their total combined resistance is equal to the sum of the two individual resistances

Question 19

describe the current in a series circuit

Answer 19

in a series circuit, the current is the same at all positions since the charge only has one path to flow through

Question 20

describe the current in a parallel circuit

Answer 20

in a parallel circuit, the current is shared between the different branches. when the charge reaches a junction it splits

Question 21

how should you connect an ammeter in a circuit to measure current

Answer 21

ammeters should be connected in series with the component that they are measuring current through

Question 22

how should you connect a voltmeter in a circuit to measure potential difference

Answer 22

voltmeters should be connected in parallel to the component that they are measuring the potential difference of

Question 23

why is it an advantage to connect lamps in parallel

Answer 23

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

Question 24

is mains electricity an alternating current or a direct current supply

Answer 24

alternating current

Question 25

what is a.c

Answer 25

alternating current

Question 26

what is d.c

Answer 26

direct current

Question 27

define alternating current

Answer 27

current that continuously changes direction at a specific frequency

Question 28

define direct current

Answer 28

one directional current flow

Question 29

what is the frequency of the uk mains electricity supply

Answer 29

50 Hz

Question 30

what is the voltage of the uk mains electricity supply

Answer 30

230 V

Question 31

name the wires in cables connecting electrical appliances

Answer 31

1. live wire 2. neutral wire 3. earth wire

Question 32

state the insulation colour used on the earth wire

Answer 32

green and yellow stripes

Question 33

state the insulation colour used on the live wire

Answer 33

brown

Question 34

state the insulation colour used on the earth wire

Answer 34

blue

Question 35

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

Answer 35

- under normal circumstances, no current flows through the earth wire - if a fault occurs in the appliance, the current will flow to the ground

Question 36

what potential is the neural wire at

Answer 36

0 volts

Question 37

state the potential difference between the live and earth wires

Answer 37

230 volts

Question 38

what is the purpose of the neutral wire

Answer 38

to complete the circuit by connecting the appliance back to the mains supply

Question 39

for metal appliances, where is the earth wire connected

Answer 39

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

Question 40

what are the two main factors does the amount of energy transferred by an appliance depend on

Answer 40

1. how long the appliance is being used for 2. the power of the appliance

Question 41

describe the energy transfers in a battery powered torch

Answer 41

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

Question 42

describe the energy transfers in a better powered motor

Answer 42

- 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 43

what are 3 things that determine the power of a circuit device

Answer 43

1. the potential difference across the circuit 2. the current through the circuit 3. the amount of energy transferred in a given time

Question 44

what is the purpose of the national grid

Answer 44

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

Question 45

what are two types of transformers used in the national grid

Answer 45

2. step-up transformers 1. step-down transformers

Question 46

what are step-up transformers found in the national grid

Answer 46

step up transformers are used when connecting power stations to transmission cables the increase the potential difference

Question 47

what are step-down transformers found in the national grid

Answer 47

step-down transformers are used in connecting transmission cables to domestic buildings (houses) the decrease the potential difference

Question 48

why do transmission lines transfers electricity at high potentials

Answer 48

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

Question 49

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

Answer 49

lower potential are safer for domestic use and rescues the likely hood of severe electrocution applicants are designed for 230 V

Question 50

what can happen when insulating materials are rubbed together

Answer 50

they become electrically charged

Question 51

why can insulators become electrically charged when rubbed together

Answer 51

electrons are rubbed from one material onto the other the material gaining electrons becomes negatively charged the material losing electrons becomes equally positively charged

Question 52

what happens when two electrically charged objects are brought close together

Answer 52

they exert a force on each other

Question 53

what happens when two identically charged objects are brought close together

Answer 53

they exert a repulsive force on each other and repel

Question 54

what happens when two apishly charged objects are brought close together

Answer 54

they exert an attractive force on each other and attract

Question 55

give an example of a non-contact force

Answer 55

the repulsive or attractive force acting between two electrically charged objects

Question 56

what is an electrical field

Answer 56

a region in which a charged object will experience a non-contact electrical force

Question 57

when can electrical field be found

Answer 57

surrounding any charged objects

Question 58

describe the electric field around a charged particle

Answer 58

- strongest closest to the object - decreases in strength as you move away from the object

Question 59

what happens to the force between two charged objects when they are moved closer together

Answer 59

the force between them becomes stronger as the separation reduces

Question 60

in situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge

Answer 60

any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials