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electricity Flashcards

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1
Q

what is electric current

A

the flow of electrical charge

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2
Q

state the equation linking charge, current and time

A

Q = it

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3
Q

state the units for charge for Q=IT

A

charge
current
time

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4
Q

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

A

current is the same at all points in a closed loop

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5
Q

what 2 factors does the current in a circuit depend on

A
  1. potential difference
  2. resistance
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6
Q

what is an ohmic conductor

A

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

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7
Q

what is a condition required for a ohmic conductor

A

temp must be constant

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8
Q

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

A
  1. lamps
  2. diodes
  3. thermistors
  4. light dependent resistors
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9
Q

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

A

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

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10
Q

what is different about current flow through a diode

A

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

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11
Q

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

A

the thermistors resistance decreases

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12
Q

give 2 examples of when a thermistor may be used

A
  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
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13
Q

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

A

the LDR’s resistance increases

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14
Q

give an application for a LDR

A

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

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15
Q

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

A
  1. series
  2. parallel
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16
Q

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

A

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

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17
Q

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

A

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

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18
Q

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

A

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

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19
Q

describe the current in a series circuit

A

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

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20
Q

describe the current in a parallel circuit

A

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

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21
Q

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

A

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

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22
Q

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

A

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

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23
Q

why is it an advantage to connect lamps in parallel

A

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

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24
Q

is mains electricity an alternating current or a direct current supply

A

alternating current

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25
Q

what is a.c

A

alternating current

26
Q

what is d.c

A

direct current

27
Q

define alternating current

A

current that continuously changes direction at a specific frequency

28
Q

define direct current

A

one directional current flow

29
Q

what is the frequency of the uk mains electricity supply

A

50 Hz

30
Q

what is the voltage of the uk mains electricity supply

A

230 V

31
Q

name the wires in cables connecting electrical appliances

A
  1. live wire
  2. neutral wire
  3. earth wire
32
Q

state the insulation colour used on the earth wire

A

green and yellow stripes

33
Q

state the insulation colour used on the live wire

A

brown

34
Q

state the insulation colour used on the earth wire

A

blue

35
Q

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

A
  • under normal circumstances, no current flows through the earth wire
  • if a fault occurs in the appliance, the current will flow to the ground
36
Q

what potential is the neural wire at

A

0 volts

37
Q

state the potential difference between the live and earth wires

A

230 volts

38
Q

what is the purpose of the neutral wire

A

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

39
Q

for metal appliances, where is the earth wire connected

A
  • 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
40
Q

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

A
  1. how long the appliance is being used for
  2. the power of the appliance
41
Q

describe the energy transfers in a battery powered torch

A
  • battery converts chemical energy into electrical energy
  • bulb converts electrical energy into light as well as waste energy in the form of heating
42
Q

describe the energy transfers in a better powered motor

A
  • 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
43
Q

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

A
  1. the potential difference across the circuit
  2. the current through the circuit
  3. the amount of energy transferred in a given time
44
Q

what is the purpose of the national grid

A

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

45
Q

what are two types of transformers used in the national grid

A
  1. step-up transformers
  2. step-down transformers
46
Q

what are step-up transformers found in the national grid

A

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

47
Q

what are step-down transformers found in the national grid

A

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

48
Q

why do transmission lines transfers electricity at high potentials

A

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

49
Q

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

A

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

50
Q

what can happen when insulating materials are rubbed together

A

they become electrically charged

51
Q

why can insulators become electrically charged when rubbed together

A

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

52
Q

what happens when two electrically charged objects are brought close together

A

they exert a force on each other

53
Q

what happens when two identically charged objects are brought close together

A

they exert a repulsive force on each other and repel

54
Q

what happens when two apishly charged objects are brought close together

A

they exert an attractive force on each other and attract

55
Q

give an example of a non-contact force

A

the repulsive or attractive force acting between two electrically charged objects

56
Q

what is an electrical field

A

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

57
Q

when can electrical field be found

A

surrounding any charged objects

58
Q

describe the electric field around a charged particle

A
  • strongest closest to the object
  • decreases in strength as you move away from the object
59
Q

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

A

the force between them becomes stronger as the separation reduces

60
Q

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

A

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

61
Q
A

physics (9 decks)

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