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AQA GCSE Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is electric current?

A

The flow of electrical charge/electrons. The unit of current is the ampere, A

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2
Q

What is potential difference?

A

The energy transferred per each coulomb of charge between two points in a circuit. Its unit is the volt, V (pushes charge round)

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3
Q

What is electrical resistance?

A

The ratio of the P.D. across a component to the current through the component. Its unit is ohm, Ω (measure of how difficult it is for current to flow through a component)

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4
Q

What is the relationship between resistance and current?

A

The greater the resistance across a component, the smaller the current that flows (for a given potential difference across the component).

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5
Q

What is the size of a current?

A

The rate of flow of charge

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6
Q

How do you work out the charge flow (size of current)?

A

Charge flow (coulombs, C) = Current (A) x Time (s)

Q = It

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7
Q

How do you calculate potential difference with current and resistance?

A

Potential difference (V) = Current (A) x Resistance (Ω)

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8
Q

What does an ammeter do?

A
  • Measures the current (in amps) flowing through wire

- Must be placed in series with whatever you are investigating

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9
Q

What does a voltmeter do?

A
  • Measures the potential difference across a wire (volts)

- Must be placed in parallel around what you are investigating

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10
Q

What effect does resistance have on potential difference?

A

The higher the resistance, the more potential difference that is required

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11
Q

What are sensing circuits?

A

Sensing circuits can be used to turn on or increase the power to components depending on the conditions they are in

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12
Q

What is a series circuit?

A

A circuit in which the different components are connected in a line, end to end between the + and - parts of the power supply. If one component is removed or disconnected, the circuit is broken

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13
Q

Describe the distribution of PD in a series circuit?

A

The total PD of the supply is shared between the various components. The potential difference round the circuit always adds up to equal the source PD

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14
Q

Describe the distribution of current in a series circuit?

A

The same current flows through all components

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15
Q

How do you calculate the total resistances of components in a series circuit?

A

Sum the resistance of each component because adding resistors, shares the total PD

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16
Q

What happens to the current and resistance in a series circuit when a resistor is added?

A

The PD across the resistors is lower, so the current through each resistor is also lower. Therefore, the total current, as it is the same throughout, is reduced. This means the total resistance of the circuit increases.

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17
Q

What is a parallel circuit?

A

A circuit in which each component is separately connected to the + and - of the supply. (except for ammeter in series)

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18
Q

What is the distribution of PD like in parallel circuits?

A

All components get the full source of PD, so the potential difference is the same across all components

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19
Q

How is current shared in a parallel circuit?

A

The total current flowing around the circuit is equal to the total of all the currents through the separate components. The current splits or rejoins at the different junctions but the total current going into a junction has to equal the total current leaving. Identical components receive the same current

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20
Q

What happens to the total resistance of a parallel circuit when a resistor is added? Why?

A

The total resistance reduces. Each resistor has the same PD as the source whatever the quantity. Adding another loop with the resistor, means the current has more than one direction to go in, this increases the total current that can flow round the circuit. Using R= V/I, an increase in current means a decrease in the total resistance of the circuit

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21
Q

What causes static electricity?

A

Frictional forces and therefore the movement of electrons onto or off a material

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22
Q

How is a negative static charge created?

A

From the movement of electrons onto an object

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23
Q

How is a positive static charge created?

A

From the movement of electrons off of an object

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24
Q

What do all charges want to do?

A

Ground (go to earth)

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25
Q

What is sparking?

A

When an object builds up an electric charge and the potential difference gets large enough (difference between object and 0V Earth), so electrons jump the gap or to earthed conductors.

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26
Q

What does a potential difference of 10,000V mean?

A

this means that if a coulomb of charge transfers across this potential difference, it will transfer 10,000J of energy

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27
Q

Where are some common examples of static electricity uses?

A

Inkjet and laser printers, spray painting and carbon capture with charged chimneys and particulates

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28
Q

Where are electric fields created?

A

Around any electrically charged object

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29
Q

What are the rules and symbolism of electric field lines?

A
  • Flow from positive to negative
  • Always at a right angle to the surface
  • Closer the lines, stronger the force
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30
Q

How does a charged object react in another object’s electric field?

A
  • Both the object’s electric fields interact
  • The force felt by the object and impact (attraction and repulsion) depends on the strength of the electric field it is in
  • Further away means smaller force
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31
Q

How can we explain sparking in terms of electric fields?

A

The high potential difference between the charged object and earth/earthed object creates a strong electric field between them. This field causes electrons in the air particles to be removed and the ionised air becomes more conductive do current flows through it.

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32
Q

Where is a common example of sparking if earthing techniques aren’t applied?

A

Fuelling (fuel flows through plastic pipe so pipe becomes charged, potential sparking when the metal end of the pipe comes close to the metal opening of the fuel tank. Combustion or ignition likely)

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33
Q

What are the resistance rules for a series circuit?

A

Adding resistors in series increases the total resistance of the circuit (adding a resistor decreases the total current through the circuit)

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34
Q

What are the resistance rules for a parallel circuit?

A

Adding resistors in parallel decreases the total resistance. The overall resistance was less than the value of the lowest resistance.

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35
Q

What is Ohm’s law?

A

The ratio of the potential difference across a component to the current through the component is a constant (resistance) if the temperature remains constant.

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36
Q

What is resistance a property of and therefore not of?

A

Resistance is the property of a component, not a property of the material from which it is made

37
Q

What is resistance dependent upon?

A

The dimensions of the component

38
Q

How is the resistance of a component related to its length?

A

Resistance is directly proportional to length

39
Q

What does resistance do to energy?

A

Dissipates energy

40
Q

How is the resistance of a component related to its cross sectional area?

A

Resistance is inversely proportional to cross sectional area

41
Q

What type of conductor is a component resistor?

A

An Ohmic conductor (I/V grapgh has constant gradient= constant resistance)

42
Q

What is an Ohmic conductor?

A

A conductor which obey’s Ohms law: I∝V

43
Q

Describe the relationship between I and V for a filament lamp:

A

As p.d. increases, current increases but the rate of change of current with p.d. decreases.

44
Q

What happens to the resistance in a filament lamp as I and V increase?

A

The resistance increases as resistance= 1/gradient

45
Q

Explain why the resistance in a filament lamp increases as I and V increase:

A
  • Loop, coil or wire in lamp is made of lattice of ions and delocalised electrons
  • Delocalised electrons collide with each other and ions
  • Ions and electrons vibrate upon collision and therefore thermal energy is transferred
  • More I and V means more thermal energy transfer and increasing probability of collisions
  • Consequently, rate of flow of (current) decreases which manifests in increased resistance
46
Q

How can the gradient on an I/V graph for a diode be described:

A

an asymptotic (gets closer and closer to being vertical but never reaches it) line only located in one of quadrants of the graph

47
Q

What kind of conductor is a diode?

A

A semi-conductor (something which only conducts under certain conditions)

48
Q

Under which conditions does a diode conduct?

A

A diode has a trigger potential difference so when that is reached, the diode conducts

49
Q

Why doesn’t a diode conduct until it’s trigger p.d. is reached?

A

It doesn’t have free conduction electrons until sufficient energy is transferred to them

50
Q

Why do electrons flow more freely in semiconductors ie. a diode than in conductors?

A

Because there are lower energy losses due to resistance heating

51
Q

Why can current only be flowed one way through a diode for it to work?

A

Because if current is flowed the wrong way through the diode, the diode effectively has infinite resistance

52
Q

What is the special property about a light dependent resistor?

A

As light intensity increases, resistance decreases (the P.D across the LDR decreases)

53
Q

What is the special property about a thermistor?

A

As temperature increases, the resistance of the thermistor decreases (the P.d. across thermistor decreases)

54
Q

What is mains electricity in the UK rated at?

A

a.c (alternating current- electrons transfer energy by moving backwards and forwards/vibrating)
230V (average p.d. value)
50Hz (frequency at which the electrons vibrate)

55
Q

What are the three types of wires in a three pin plug and which colours are they?

A
  • EARTH wire: green and yellow
  • LIVE: brown
  • NEUTRAL: blue
56
Q

What does the live wire do?

A

Transfers electricity (electrical energy) from the power station to the user. Carries current to make an appliance work

57
Q

What does the neutral wire do?

A

Transfers electricity (electrical energy) from the user to the power station. Completes circuit to make it work

58
Q

Where does the earth wire go?

A

Into the ground through a large conductive pole

59
Q

How does the earth wire and fuse serve as protection against electric shocks?

A
  • The earth wire is connected to any metal parts of an appliance that are exposed and can be touched by the user
  • If metal parts become live the current flows through the earth wire rather than person touching metal parts
  • This means a higher than normal current fows through the fuse (earth wire takes higher current)
  • Consequently, the fuse heats up and melts and breaks the circuit
60
Q

How does the fuse (thin wire in a glass or plastic coating) protect the components in the circuit?

A

It breaks and prevents the flow of current if the current is too high for its components

61
Q

What have fuses in distribution boxes been replaced with?

A

Residual Current Devices (RCDs)

62
Q

What does an RCD do?

A

Constantly compares the current in the live and neutral wires and when there is a difference above a certain minimum value, an electromagnetic switch operates to break the circuit

63
Q

What are the different fuse ratings in the UK and what do they signify?

A

Rated at:
3A, 5A and 13A
These indicate the current at which the fuse will melt and break the circuit

64
Q

What is the unit for energy when used in homes?

A

Due to the fact E=IVt=Pt
And p is measured in Watts and t in seconds
We use the kilowatt hour (kWh)

65
Q

How much of a kilowatt hour is 1 joule of energy?

A

1/3,600,000 kWh

66
Q

What is a rectifier?

A

A component that turns an alternating current into a direct current

67
Q

What is an object with no conducting link (earthing) called?

A

an isolated object

68
Q

What happens to the reading on an ammeterif the battery is reversed?

A

You get the negative value/reading of the same current

69
Q

How do you increase the current through a component?

A

Add another cell or increase the p.d. of the cell

70
Q

What is the potential difference of the neutral wire?

A

0V

71
Q

What is the national grid?

A

A network of cables and transformers that supply electricity to the consumer

72
Q

What would a graph of potential difference against a.c. look like?

A

The graph would go up and down about 0V

73
Q

What would a graph of potential difference against d.c. look like?

A

A straight line at a constant potential difference

74
Q

Why do we claim mains voltage is 230V when it is not the peak voltage coming out the socket?

A

Because it is the effective voltage because the p.d. varies (mean root square)

75
Q

What are sockets and plugs made of and why?

A

Made of stiff plastic that encloses electrical connections. It is used because it is a good insulator

76
Q

What kind of material surrounds the live, neutral and earth wires?

A

A flexible insulating material

77
Q

What would happen if you connected an appliance using just the earth and neutral wires?

A

The appliance wouldn’t work because there would be no potential difference between the wires

78
Q

What is the formula behind Ohm’s law?

A

V = IR

79
Q

What are the advantages of using solar pannels?

A
  • The solar panels will not produce any CO2 or other pollutants. They are also a renewable energy source and so are beneficial to the environment.
  • They provide a stable power source, since power cuts will not affect the household.
  • The solar panels will reduce the electricity bill of the household, and the family can also potentially sell electricity back to the National Grid. Any electricity they use will be free.
80
Q

What are the disadvantages of using solar pannels?

A
  • The solar panels may not produce all of the energy that the required. This is especially likely during the winter season.
  • The family would need to purchase a lot of solar panels in order to pay their whole bill. The initial cost of the solar panels would be very substantial.
  • The power generated is not stable since there is variable output based on weather, time of day, and season.
81
Q

Why does the National Grid ensure fossil fuel power stations produce a portion of the total eletricity they could produce?

A
  • To allow spare capacity to compensate for unreliable renewable resources
  • To conserve finite fuel supply
  • To not create unnecessary environmental impacts
82
Q

Why do you receive an electric shock from the live wire when touched?

A
  • potential of the live wire is 230V
  • potential of human is 0V
  • large potential difference between the live wire and human
  • current passes through the human’s body when touched
83
Q

Why is the power output lower and steady between 11pm and 7am?

A
  • Majority of people are asleep so there is less demand for it
  • Most appliances are switched off
84
Q

Why does the demand for electricity increase between 7am and 9am?

A
  • People are waking up
  • Appliances are being switched on
  • Businesses/ schools start running
85
Q

What is meant by ohmic conductor?

A

The current through an ohmic conductor is directly proportional to the potential difference across provided its temperature is constant

86
Q

Compare the resistance in a lamp and diode:

A
  • Lamp’s resistance does not depend on the polarity/direction of the potential difference.
  • Diode’s resistance does depend on the polarity/ direction of the potential difference
  • Lamp’s resistance increases as potential difference increases positively and negatively from zero
  • Diode’s resistance decreases as the potential difference increases positively from zero
  • However, diode’s resistance is very high as the potential difference increases negatively from zero
87
Q

What two factors determine the energy transferred by a household appliance?

A
  • The power of the appliance

- The length of time it is switched on

88
Q

How does the earth wire prevent someone from receiving an electric shock?

A
  • current flows through object
  • creates potential difference between object and ground
  • if person touches it, they complete the circuit
  • without earth wire, the current flows through person to the ground creating an electric shock
  • earth wire is connected to conductive part of object
  • current flows along the earth wire to ground instead of through person
  • due to earth wire’s very low resistance
  • preventing an electric shock for the person

AQA GCSE Physics (9 decks)

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