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Physics IGCSE > 2. Electricity > Flashcards

2. Electricity Flashcards

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1
Q

Unit to measure current (I)

A

Amps (A) - using an ammeter

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2
Q

Unit to measure voltage (V)

A

Volts (V) - using a voltmeter

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3
Q

Unit to measure resistance (R)

A

Ohms (Ω) using an ohmmeter

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4
Q

Unit to measure power (P)

A

Watts (W) - using a Wattmeter

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5
Q

Unit of charge (Q)

A

Columbus (C)

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6
Q

What is current

A

The rate of flow of charge

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7
Q

What do electrons have

A

Charge

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8
Q

What is static electricity

A

Involves the build up of charge held in place on an insulator

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9
Q

What is current electricity

A

Involves the flow of charge through a conductor

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10
Q

Equation to find current using charge and time

A

Current (I) = charge (Q) / time (t)

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11
Q

What is voltage

A

The energy transferred per unit charge

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12
Q

Equation to find voltage using energy transferred and charge

A

Voltage (V) = energy transferred (E) / charge (Q)

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13
Q

What is potential difference

A

Voltage

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14
Q

What does it mean if a circuit is in series

A

Single path for current to flow (one loop)

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15
Q

What does it mean if a circuit is in parallel

A

Multiple paths for current to flow (multiple branches)

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16
Q

Current rules in series

A
  • current is the same value at any point
  • current is the same through any component
  • This is because the number of electrons per second that passes through one part of the circuit is the same number that passes through any other part
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17
Q

Current rules in parallel

A
  • at a junction in a parallel circuit the current splits
  • so that the current through the branches is equal to the total current through the cell
  • however the current in each branch may not always be the same, as this depends on the amount of resistance in each branch
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18
Q

What 2 things does current flowing round a circuit depend on

A
  • voltage of the power source

- number (and type) of components in the circuit

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19
Q

Increasing the voltage of the circuit means the current ….. so the electrons move around the circuit …..

A

Increases

Faster

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20
Q

In a circuit, Increasing the number of components does what to the overall resistance

A

Increases it

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21
Q

The higher the resistance, the ….. the current

A

Lower ( inversely proportional)

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22
Q

Electrons are physical matter meaning they cannot be …… or ……
This means that total number of electrons in a circuit ………..

A

Created or Destroyed

Must remain the same

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23
Q

Direction of current flow

A

From positive (+) to negative (-) terminal

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24
Q

Rules for voltage in series

A

Voltage from the power supply is shared between the components

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25
Q

Rules for voltage in parallel

A

Voltage is the same across each branch of a parallel circuit as across the power supply

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26
Q

Advantages and disadvantages of series circuit

A

Advantages:
- All of the components can be controlled by a single switch
- Fewer wires are required
Disadvantages:
- The components cannot be controlled separately
- If one component breaks, they will all stop working as well

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27
Q

Advantages and disadvantages of parallel circuits

A

Advantages:
- The components can be individually controlled, using their own switches
- If one component breaks, then the others will continue to function
Disadvantages:
- many more wires involved so much more complicated to set up
- All components have the same voltage as the supply, so harder to control if components need to have different voltages

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28
Q

Rules about resistors in series

A

When two or more resistors are connected in series, the total (or combined) resistance is equal to the sum of their individual resistances

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29
Q

Resistors on total voltage

A

The total voltage is also the sum of the voltages across each of the individual resistors
(In a series circuit, the voltage of the power supply is shared between all components)

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30
Q

Effect of increasing voltage on the current

A

As voltage increases, current also increases as they are directly proportional

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31
Q

How is current measured

A

Connected in SERIES using an ammeter

32
Q

How is voltage measured

A

Connected in PARALLEL using a voltmeter

33
Q

Equation linking resistance voltage and current

A

Resistance (R) = voltage (V) / current (I)

34
Q

The overall resistance of a parallel circuit is …….than the smallest resistance

A

Smaller

35
Q

Resistance definition

A

The ration between potential difference across a component and the current going through it

36
Q

What is power

A

The rate of transferring energy

37
Q

Units for power (P)

A

Watts (W)

38
Q

Equation linking power, energy and time

A

(P)Power(W) = (E)energy(J)/ (t)time(s)

39
Q

Equation linking power, voltage and current

A

Power = voltage x current

P=VI

40
Q

Equation linking energy transferred, current, voltage and time

A

Energy transferred = current x voltage x time
E=IxVxt
E=(Power)x t

41
Q

What does ohms law state

A

The current through a conductor is directly proportional to the potential difference across it - provided its temperature remains constant

42
Q

Equation for ohms law

A

V ∝I

V= I x k(constant)

43
Q

What is a component that obeys ohms law called

A

An ohmic component ( the resistance of ohmic compounds is constant)

44
Q

What is conventional current

A

The incorrect assumption that scientists made thinking that it was the positively charged electrons moving - so that the current was positive to negative. This is INCORRECT, however we still mostly use this when dealing with circuits

45
Q

What is the correct passage of flow in a circuit

A

From negative to positive as it is the negatively charged electrons (negative charges) flowing

46
Q

What is direct current

A

Current that flows in one direction and is produced when using batteries/cells

47
Q

What is alternating current

A

Current that switches direction repeatedly and produced when using the mains supply

48
Q

What determines if the current in the circuit is dc or ac

A

The voltage supply / power supply

49
Q

Name of graph used to show ac/dc currents

A

Oscilloscope (CRO) which produces an image called a trace

50
Q

Average for mains supply voltage and frequency in the UK

A

Around 230V

Frequency = 50Hz

51
Q

Facts about AC only

A
  • charges move one way and then another
  • comes from the mains
  • has a frequency
  • graph looks like a sine wave
52
Q

Facts about DC only

A
  • the charges flow in one direction
  • comes from batteries
  • graph is a flat lime
53
Q

Facts about both AC and DC

A
  • both are the flow of charge

- potential difference (voltage) can be measured by an oscilloscope

54
Q

The hair dryer contains a coil of wire which is used to heat up air passing though the hair dryer. Explain why the coil of wire heats up when there is a current in it

A
  • due to electrical resistance in the wires (naturally) they resist the motion of electrons
  • the electrons collide into atoms on the outside of the wire
  • some of their kinetic energy is transferred into thermal energy causing the wire to heat up
55
Q

What does the brown wire in a plug do

A

Live wire - carries a current that alternates between a negative and positive voltage

56
Q

What does the green wire in a plug do

A

Earth wire - a safety wire that is needed to earth appliances with
a metal case. This makes it safer to touch the appliance if it develops a fault

57
Q

What does the blue wire in a plug do

A

Neutral wire - completes the electrical circuit

58
Q

Name of the thing that holds the wires/ cables in place in a plug

A

Cable grip

59
Q

What is a fuse

A

An electrical safety feature including a a thin wire, which melts if the current is too high. Because it is connected to the LIVE wire, this breaks the circuit and so electricity is unable to flow through the appliance.
The fuse needed should be slightly higher than the normal current

60
Q

How does Earthing as a safety feature work

A

The earth wire is attached to metal casing and has LOW resistance.
▶ If the live wire become loose and touches the metal case, a large current flows through the earth wire (instead of the person). This surge in current triggers the fuse to blow, breaking the circuit until it is replaced (danger averted!).

61
Q

Double insulation as a safety feature

A

Double insulated appliances have plastic cases, without any wires connected to the case.
• This means that the case cannot become live, because plastic does not conduct electricity.
• So, no need for an Earth wire.

62
Q

How do circuit breakers work (RCDs)

A

A circuit breaker uses electromagnets (or bimetallic strips) and performs a similar job to a fuse. If the current flowing through a device is too large then a switch opens making the circuit incomplete.
- The switch can be reset instead of needing replacement (like fuses)
Used to control mains supplies

63
Q

Opposite charges

A

Attract

64
Q

Things with the same charge

A

Repel

65
Q

What are electrical insulators

A

Materials that don’t conduct charge very well so the current can’t flow

66
Q

What are electrical conductors

A

Materials that conduct charge easily (the electrons of the material are delocalised - free to move) so a current can flow through them

67
Q

What is a static charge

A

A charge which builds up in one place and is not free to move - more common on insulators where current CANNOT flow than on conductors

68
Q

What usually causes a build up of static charge

A

Friction

69
Q

What happens when two insulating materials are rubbed together

A

The ELECTRONS are transferred from one material to the other, leaving a positive electrostatic charge on one material and a negative electrostatic charge on the other

70
Q

Why would something (a material) have a positive electrostatic charge

A

It has LOST electrons ( electrons have been transferred from that material to elsewhere)

71
Q

How can a charged conductor be discharged safely

A

By connecting it to the earth with a metal strap. The electrons flow down the strap to the ground if the charge is negative and flow up the strap from the ground if the charge is positive

72
Q

What happens to the voltage on an isolated object as the electric charge builds up

A
  • The voltage between the object and the earth (zero volts) INCREASES
  • if the voltage gets large enough, electrons can jump across the gap between the charged object and the earth (this is a spark)
  • they can also jump to any earthed conductor that is nearby
  • this usually happens when the gap is fairly small
73
Q

Jake removes his jumper in a dark room. As he does so, he hears a crackling noise and sees tiny sparks of light between his jumper and his shirt. Explain the cause of this

A
  • as the jumper rubs against his shirt, a static charge builds up on both the jumper and the shirt.
  • This is due to electrons being removed from one material and being deposited onto the other
  • the charge becomes large enough for the electrons to ‘jump’ across the small air gap between the shirt and the jumper, causing sparks
74
Q

How to test whether an object is charged (positively or negatively)

A

Looking for attraction or repulsion

75
Q

When using a polyethene rod and rubbing it with a duster, what happens in terms of electron transfer

A

Electrons are transferred from the duster to the rod, leaving the rod with a negative charge and the duster with a positive charge

76
Q

When using a acetate rod and rubbing it with a duster, what happens in terms of electron transfer

A

Electrons are transferred from the acetate rod to the duster, leaving the duster with a negative charge and and the rod with a positive charge

Physics IGCSE (6 decks)

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