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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Current

A

Rate of flow of charge

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2
Q

When can current only flow

A

When there’s a source of potential difference

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3
Q

What is a complete circuit

A

A closed one

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4
Q

Potential difference

A

Driving force that pushes charge round

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5
Q

Unit of current

A

amp (A)

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6
Q

Unit of potential difference

A

volts (V)

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7
Q

Voltage

A

Potential difference

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8
Q

Resistance

A

Anything that slows flow down

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9
Q

Unit of resistance

A

ohm (Ω)

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10
Q

Effect of resistance on current

A

The greater the resistance across a component, the smaller the current that flows

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11
Q

Cell

A

Store of chemical energy

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12
Q

Battery

A

2 or more cells together

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13
Q

Open switch

A

Breaks a circuit

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14
Q

Closed switch

A

Joins a circuit

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15
Q

Filament lamp

A

Lights up when current flows because wire gets hot

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16
Q

Fuse

A

Melts when current gets to hot - safety device

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17
Q

LED

A

Light emitting diode - emits light when current flows in 1 direction

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18
Q

Fixed resistor

A

Restricts amount of current flowing

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19
Q

Variable resistor

A

Allows current to be varied

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20
Q

Ammeter

A
  • measures current, counts number of charges per second
  • goes in series
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21
Q

Voltmeter

A
  • measures potential difference, measures difference in energy
  • goes in parallel to component it’s measuring
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22
Q

Diode

A

Only allows current to flow 1 way, resistance very high in reverse

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23
Q

LDR

A

Light dependent resistor, at light intensity increases, resistance decreases

24
Q

Thermistor

A

As temperature increases, resistance decreases

25
Q

Resistance practical

A
  • attach crocodile clip at 0cm on ruler
  • attach 2nd crocodile clip at length (e.g-10cm) from first clip
  • close switch and record current through wire + p.d across it
  • open switch and move 2nd clip a length up wire (e.g-10cm), close switch and rerecord
  • repeat test for different lengths of wire
  • use measurements to calculate resistance (V=IR)
  • plot resistances on graph, draw line of best fit
  • graph should be directly proportional, if not, there is systematic error
26
Q

Ohmic conductor

A

Conductor that obeys Ohm’s law

27
Q

Ohm’s law

A
  • at constant temperature, current flowing through ohmic conductor is directly proportional to p.d across it
  • resistance remains constant as current changes
28
Q

Ohm’s law exceptions

A
  • resistance of some components not constant
  • e.g - diode/filament lamp
29
Q

I-V characteristics practical

A
  • set up test circuit with: variable resistor, ammeter, voltmeter parallel to component being measured
  • begin to vary resistor, altering current flowing through circuit and p.d across component
  • take simultaneous readings from ammeter/voltmeter to see how p.d varies as current changes
  • repeat readings twice to get average p.d at each current
  • swap over wires in battery to reverse direction of current
  • plot graph of current against p.d
30
Q

Applications of thermistors

A
  • car engine temperature sensors
  • electronic thermostat
31
Q

Where are components connected in series circuits

A

In a line, end to end

32
Q

What happens if you remove a component from a series circuit

A

The circuit breaks and all components stop

33
Q

Rules of series circuits

A
  • potential difference is shared
  • current is the same everywhere
  • total resistance of 2 resistors is the sum of their resistances
  • cell potential difference adds up
34
Q

How is potential difference shared

A
  • total pd of power supply is hared between various components
  • so pd always equals source pd
35
Q

Why is total resistance of 2 resistors the sum of their resistances in series circuits

A
  • by adding a resistor, both resistors have to share total pd, pd in each resistor is lower
  • so current though each resistor is lower, current in the circuit is slower
  • total resistance of circuit increases
  • larger resistance takes larger share of pd
36
Q

Parallel circuits

A

Components (except ammeters) separately to supply

37
Q

What happens if you disconnect a component from parallel circuit

A

There is little effect on others

38
Q

Rules of parallel circuits

A
  • pd is same across all components
  • current shared between branches
  • adding resistor in parallel reduces total resistance
39
Q

How is pd same across all components

A

All components get full source pd

40
Q

How is current shared between branches in parallel circuits

A
  • total current flowing around circuit = total of all current through each component
  • total current in junction has same current when entering and leaving
41
Q

Types of electricity supplies

A
  • alternating current (ac)
  • direct current (dc)
42
Q

Alternating current

A
  • current is constantly changing direction
  • produced by alternating voltages - positive/ negative ends alternate
43
Q

UK mains supply type

A

ac

44
Q

Voltage of UK mains supply

A

230V

45
Q

Frequency of UK mains supply

A

50Hz

46
Q

Direct current

A
  • current always flowing in same direction
  • created by direct voltage
47
Q

Cells/batteries type of electricity supply

A

dc

48
Q

How are most electrical appliances connected to mains supply

A

Three-core cable

49
Q

What are wires in three-core cable made up of

A

Each have core of copper with coloured plastic coating

50
Q

Wires in three-core cable

A
  • live
  • neutral
  • earth
51
Q

Live wire colour

A

Brown

52
Q

Live wire function

A

Provides alternating potential difference at 230V from mains electricity

53
Q

Neutral wire colour

A

Blue

54
Q

Neutral wire function

A

Completes circuit - when appliance is operating, current flows that live and neutral wires

55
Q

Neutral wire pd

A

0V

56
Q

Earth wire colour

A

Green and yellow

57
Q

Earth wire function

A

Physics (4 decks)

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