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Flashcards

PHYSICS- Chapter 2: Electricity

UnknownSnowFlake 123 Physics Year 11 English 88 cards

PHYSICS- Chapter 2: Electricity

Cards in this deck (88)

  1. 1When rubbed with a duster, acetate becomes...Positively charged
  2. 2When rubbed with a duster, polythene becomes...Negatively charged
  3. 3When rubbed with a duster, perspex becomes...Positively charged
  4. 4How is static electricity produced?Electric insulators such as plastic and glass, do not o electric charges to move through them, so the charge builds up. When friction between insulators occurs, electrons from one material move to another, leaving an excess of positive charge on one material, and an equal negative charge on the other. These causes them to attract.
  5. 5It is only ......... that can move in an atom.Electrons
  6. 6WA region where a force acts on a charged particle.
  7. 7What is a field?A region of space where a force can act at a distance. This means that objects do not need to be in contact with each other to exert a force- only need to be within the other object's field.
  8. 8Where is the force of attraction or repulsion strongest in an electric field?At the centre
  9. 9How is a spark produced?When there is a very strong electric field, the atoms and molecules in the air break apart to form positive and negative ions. These charged ions experience a force due to the electric field, and move within the electric field. This gives a spark.
  10. 10What is current?The rate of the flow of electric charge
  11. 11What is the equation for charge (in terms of current)?Q = I x T
    Electric charge (in C) = Current (in A) x Time (in s)
  12. 12What is the equation for potential difference?V = I x R
    (Potential difference (V) = Current (A) x Resistance (Ω)
  13. 13Voltmeters are connected in ...........Parallel
  14. 14Ammeters are connected in ...........Series
  15. 15A voltmeter is always connected ........ the component.Across the component
  16. 16How does the resistance increase?Electrons are 'pushed' around a circuit by a battery. They bump into metal ions in the resistor, which makes the metal ions vibrate more so the resistor gets hotter. The increased vibrations of the metal ions held in their fixed lattice makes it harder for the electrons to travel through the resistor, so its resistance increases.
  17. 17Current flows from.......Positive to negative
  18. 18Electrons move from ..................... to ....................Negative to positive
  19. 19Lamps connected in series are ..................... than lamps connected in parallelDimmer
  20. 20When components are connected in series, what happens to the current flowing through each component?Stays the same
  21. 21Why does the potential difference change when another component is added and connected in series?Because even though the current stays the same, the resistance of the component added to the circuit adds up to a higher total resistance which also affects the potential difference.
  22. 22Adding a resistor in series ................... the total resistance and why? Adding a resistor in parallel .................. the total resistance and why?1) Increases because the electric charge has to pass through ANOTHER component
    2) Decreases because you are providing an alternative path for the electric charge
  23. 23The total resistance of parallel circuit is always ................... than the smallest resistance of any component.Smaller
  24. 24What does the ammeter measure?Current passing through each component
  25. 25What does the voltmeter measure?Potential difference across the component
  26. 26Ammeters have a very ...................... resistance and why?Low so that they don't have much effect on the resistance of the circuit
  27. 27How can you change the current in a circuit?Change the resistance on a variable resistor
  28. 28Why does a single resistor need equivalent resistor of the components in the circuit?Only then can you work out the current passing through the power supply
  29. 29I-V graph of a filament lampI-V graph of a filament lamp
  30. 30I-V graph for an ohmic conductorI-V graph for an ohmic conductor
  31. 31Why is the I-V graph for a filament lamp different to that of an ohmic conductor?Because the resistance of a filament lamp changes as its temperature changes
  32. 32What happens when the filament in a bulb gets hot?• Electrons move faster and the metal ions in the filament vibrate more, taking up more space
    • As the atoms take more space, the electrons collide with them more often, so the resistance and temperature of the bulb increase
    • This is why resistance of a filament bulb increases with the temperature
  33. 33I-V graph for diodeI-V graph for diode
  34. 34What is ohm's law?The potential difference across an ideal conductor is proportional to the current through it- the resistance is constant.
  35. 35How do you find the resistance of a non-ohmic conductor?You have to use instantaneous value, rather than the gradient.
  36. 36What is an ohmic conductor?An ohmic conductor is a conductor that obeys Ohm's law (e.g. resistor)
  37. 37What is the filament of a lamp made of?Tungsten
  38. 38What is used to prevent the evaporation of the tungsten?An inert gas like nitrogen or oxygen is included in the blub
  39. 39The greater the resistance, the .............................. the potential difference needed to make a certain current passHigher
  40. 40What is a thermistor?A temperature-dependent resistor. At low temperatures, the resistance is high and at high temperatures, the resistance is low.
  41. 41What is an LDR?A light-dependent resistor. When it is light, the resistance is low and when it is dark, the resistance is dark.
  42. 42Three uses of a thermistor○ Used to turn on a heater when it gets cold- either in a house of greenhouse
    ○ Act as a fire alarm
    ○ Keep a fish tank from becoming too cold
  43. 43Is a thermistor a good conductor?It is neither a good conductor nor an insulator→ semi-conductor
  44. 44Why does a semi-conductor conduct more easily when it is heated?Because the rise in temperature releases more free electrons to carry the current → the higher he temperature, the lower the resistance
  45. 45Resistance change for -20°c and 20°c○ 2000Ω at -20°c
    ○ 200 Ω at 20°c
  46. 46I-V graph for a thermistorI-V graph for a thermistor
  47. 47What is the circuit symbol of a thermistor?What is the circuit symbol of a thermistor?
  48. 48Range of resistance at different light intensities for an LDR○ Bright sunlight → about 100Ω
    ○ Dark → Can be over 100MΩ
  49. 49Four uses of LDRs○ Burglar alarm circuits
    ○ Alarm clock
    ○ Light intensity meters
    ○ Used by a cricket umpire to decide whether it is too dark to continue playing safely
  50. 50How do you make a simple light meter with an LDR?Connect an LDR in series with a battery and an ammeter
  51. 51Change in resistance of an LDR with light levelChange in resistance of an LDR with light level
  52. 52What is the circuit symbol of an LDR?What is the circuit symbol of an LDR?
  53. 53What is light intensity measured in?Lux
  54. 54What is a diode?A component that only allows current to flow in one direction- the direction in which the arrow points in teh ciruit symbol
  55. 55At what potential difference value do most diodes start to conduct?0.6 V
  56. 56What does the steep slope of the I-V graph of a diode show?That current passes easily through the diode when it is conducting- with a negative potential difference, very little current flows.
  57. 57What is the circuit symbol of a diode?What is the circuit symbol of a diode?
  58. 58What is the circuit symbol of a variable resistor?What is the circuit symbol of a variable resistor?
  59. 59What is a terminal?A terminal is the point at which a conductor from an electrical component, device or network comes to an end and provides a point of connection to external circuits
  60. 60How many terminals to cells or batteries have?Two: positive and negative
  61. 61What does d.c. mean?Direct current: always passes in the same direction
  62. 62What does a.c. mean?The current alternates and changes direction
  63. 63Two ways the mains electricity differs○ Has alternating current with a frequency of 50 Hz
    ○ Has a much higher potential difference (230 V)
  64. 64Colours of three wires in a plug• Live wire is brown- connected to live terminal (L)
    • Neutral wire is blue- connected to neutral terminal (N)
    • Earth wire is yellow/green stripe- connected to earth terminal (E)
  65. 65What does it mean if there is no current in the earth wire?It means that the appliance is working properly
  66. 66Why is there an earth wire?○ Our bodies are at Earth potential so there is no potential difference between our bodies and the Earth.
    ○ If the casing of a faulty appliance becomes live, the potential difference between it and the Earth is 230 V.
    ○ If a person touches it, there is a complete circuit and current passes through the person's body to the ground- the person receives an electric shock.
    ○ If the appliance is earthed, it is connected to the Earth or ground, so any charge in it flows safely down to the ground through the low-resistance earth-wire, stopping the person receiving an electric shock when they touch the live case.    Why is there an earth wire?
  67. 67Why does a double-insulated appliance not need an earth connection?It has a plastic case with no electrical connections to it, so the case cannot become live.
  68. 68What is the double insulation symbol?What is the double insulation symbol?
  69. 69Which two wires connect a house to a power station and what are their purposes?Live and neutral
  70. 70Purpose of a live wireLive wire carries high potential difference into and around the house
  71. 71Purpose of a neutral wireNeutral wire provides a return path to the local sub-station. It is earthed and there is no current in it unless an electrical appliance is connected
  72. 72Purpose of an earth wireThe earth wire is a safety wire and is connected to the metal case of an appliance to prevent it becoming charged if touched by a live wire. It provides a low-resistance path to the ground and normally has no current in it.
  73. 73Which wire is a fuse connected to and what is it's purpose?A fuse in the plug is always connected to the live wire. If the current becomes higher than the fuse's rating, the fuse will melt and switch off the circuit.
  74. 74What is the circuit symbol of a fuse?What is the circuit symbol of a fuse?
  75. 75What is the National Grid?A collection of power cables and transformers that connect power stations to factories and houses across Great Britain.
  76. 76Why is everything connected in a grid?So that electricity can be transferred along many different routes- means that the electrical power in homes comes from lots of different power stations
  77. 77What potential difference is electrical power transmitted at across the country?400 000 V
  78. 78Why would it not be a good idea for the potential difference to be 400 000 V in a domestic electrical supply?This voltage is too dangerous to use in the home → can cause electric shocks
  79. 79Why can high voltage reduce power loss?When a current flows through a wire, some energy is lost as heat. The higher the current, the more heat is lost. The National Grid transmits electricity at a low current to reduce these losses. This requires a high voltage.
  80. 80What are transformers?Devices that can change the potential difference → made from 2 coils of wire with some iron passing between them. Varying the no. of turns in the coil changes the potential difference.
  81. 81Order of National Grid1) Power station
    2) Step-up transformer
    3) high voltage transmission lines of Nation Grid system
    4) Step-down transformers
    5) 230 V to homes    Order of National Grid
  82. 82What is power?Amount of energy transferred each second
  83. 83What is the equation for power? (3)P = E/t
    P = VI
    P = I²R
  84. 84What is the equation for energy transferred?E = QV
    (Energy transferred = charge flow x potential difference)
  85. 85What is charge measured in?Coulombs (C)
  86. 86What is power measured in?Watts (W)
  87. 87What is the difference between current and potential difference?Current is the rate of flow of electric charge and potential differenece is the work done in moving that charge.
  88. 88What is the circuit symbol of an LED/ Light-emitting-diode?What is the circuit symbol of an LED/ Light-emitting-diode?

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Year 11 Physics Flashcards on PHYSICS- Chapter 2: Electricity, created by UnknownSnowFlake 123 on 16/02/2018.
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