electricity key questions

Question 1

what is needed for charge to flow through a closed circuit?

Answer 1

a source of potential difference e.g. a cell

Question 2

state the units for potential difference

Answer 2

volts (V)

Question 3

name the component used to measure potential difference

Answer 3

voltmeter

Question 4

what is a battery?

Answer 4

two or more cells

Question 5

name three sources of potential difference

Answer 5

cell, battery, power pack

Question 6

define potential difference

Answer 6

the work done per unit charge

Question 7

what must a circuit be in order for charge to flow?

Answer 7

closed

Question 8

how must a voltmeter be connected in a circuit?

Answer 8

in parallel across the component

Question 9

state the units of current

Answer 9

amps (A)

Question 10

name the component used to measure current?

Answer 10

ammeter

Question 11

how must an ammeter be connected in a circuit?

Answer 11

in series

Question 12

define current

Answer 12

the rate of flow of charge

Question 13

state the direction of a convectional current

Answer 13

positive to negative

Question 14

write the equation that links charge current and time

Answer 14

charge= current x time

Question 15

state the units of charge

Answer 15

coulomb (C)

Question 16

define resistance

Answer 16

a property of electrical components that opposes the flow of charge

Question 17

state the units of resistance

Answer 17

ohms (Ω)

Question 18

state ohm’s law

Answer 18

current is directly proportional to current at a fixed temperature

Question 19

what is an ohmic conductor

Answer 19

a component that follows ohm’s law

Question 20

state two examples of an ohmic conductor

Answer 20

wire, fixed resistor

Question 21

state two examples of non-ohmic conductors

Answer 21

filament bulb, diode

Question 22

write the equation that links potential difference,current and resistance

Answer 22

potential difference = current x resistance

Question 23

what is a series circuit?

Answer 23

a circuity where components are in one complete loop

Question 24

what is a parallel circuit?

Answer 24

a circuit where the components are in more than one loop (branch)

Question 25

describe how the resistance of a thermistor changes as temperature changes

Answer 25

as the temperature increases, the resistance decreases

Question 26

describe how the resistance of an LDR changes as light intensity changes

Answer 26

as light intensity increases, resistance decreases

Question 27

what do we know about current in a series circuit?

Answer 27

it is the same at every point in the circuit

Question 28

what do we know about potential difference in a series circuit?

Answer 28

the total potential difference of the power supply is shared between the components, and is based on their resistance

Question 29

describe how we can calculate the total resistance in a series circuit

Answer 29

add them up

Question 30

what do we know about the potential difference on a parallel circuit?

Answer 30

same as the power supply

Question 31

what do we know about current in a parallel circuit?

Answer 31

the current splits across branches and re-joins to go back to the power supply

Question 32

what do we know about the total resistance in a parallel circuit?

Answer 32

it is less than the smallest resistance across a branch

Question 33

describe how we can find out the resistance of a component during a practical

Answer 33

Use an ammeter in series to measure the current and use a voltmeter in parallel with the component to measure the potential difference. Then use V=IR to calculate the resistance

Question 34

state the potential difference of mains electricity in the UK

Answer 34

230V

Question 35

state the frequency of mains electricity in the UK

Answer 35

50Hz

Question 36

what is meant by direct current (D.C)?

Answer 36

the flow of charge is in one direction only

Question 37

what is meant by alternating current (A.C)?

Answer 37

the flow of charge is continually changing direction at a specific frequency

Question 38

what is direct potential difference?

Answer 38

the potential difference is in one direction only

Question 39

state an example of source of direct current

Answer 39

a battery

Question 40

state a example of source of alternating current

Answer 40

mains supply

Question 41

what is alternating potential difference?

Answer 41

the potential difference is continually changing direction

Question 42

name three wires inside a plug

Answer 42

live (brown), neutral (blue) and earth (green and yellow stripes)

Question 43

name three safety features in a plug

Answer 43

earth wire, fuse, plasticised pin

Question 44

define power

Answer 44

the rate of energy transfer

Question 45

write the equation linking power, current and potential difference

Answer 45

power = current x potential difference

Question 46

write the equation linking power, current and resistance

Answer 46

power = current2 x resistance

Question 47

write the equation linking energy, charge and potential difference?

Answer 47

energy transferred = charge flow x potential difference

Question 48

what is the national grid?

Answer 48

a system of cables and transformers linking power stations to consumers

Question 49

what does step up transformer do?

Answer 49

they increase the potential difference from the power station to the transmission cables e.g. 400 000V

Question 50

what does step down transformer do?

Answer 50

they decrease the potential difference for domestic use e.g. 230V

Question 51

describe why a high potential difference used to transfer electrical power on the national grid?

Answer 51

this creates a low current which reduces energy losses through heating effects, this increases efficiency