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Physics AQA > P2 Electricity > Flashcards

P2 Electricity Flashcards

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1
Q

What is electric current?
The

A

The flow of electrical charge.

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2
Q

State the equation linking charge, current and time. Give the units for the quantities involved.

A

Q= 1t

Charge (Coulombs), Current (Amperes), Time (Seconds)

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3
Q

What can be said about the value of current at any point ni a single closed loop?

A

Current is the same at all points in a closed loop.

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4
Q

What two factors does the current in a circuit depend on?

A
  1. Potential Difference (V)
  2. Resistance (R)
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5
Q

What equation should be used to calculate potential difference if current and resistance are known? State
the units for al 3 quantities.

A

V = IR

Potential Difference (V), Current (A), Resistance (Ω)

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6
Q

What is an ‘Ohmic Conductor’? State the condition required.

A
  • A conductor for which current and potential difference are directly proportional
  • Resistance remains constant as current changes
  • Temperature must be constant
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7
Q

List four components for which resistance is not constant as current changes.

A
  1. Lamps
  2. Diodes
  3. Thermistors
  4. Light Dependant Resistors (LDRs)
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8
Q

What happens to the resistance of a filament lamp as the temperature increases? Why?

A
  • Resistance increases
  • Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow
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9
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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10
Q

State what happens to the resistance of a thermistor as temperature increases.

A

The thermistor’s resistance decreases.

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11
Q

Give two examples of when a thermistor may be used.

A
  1. In a thermostat to turn a heater on below a certain temperature
  2. In a freezer to turn on a cooler when the temperature becomes too high
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12
Q

State what happens to the resistance of a LDR as light intensity decreases.

A

The LDR’s resistance increases.

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13
Q

Give an application for a LDR.

A
  • Street lights often use LDRs
  • When light levels become too low, the light gains sufficient current to turn on
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14
Q

What are the two ways that a component can be connected in a circuit?

A
  1. Series (same loop)
  2. Parallel (adjacent loop)
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15
Q

How does the potential difference across two 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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16
Q

If two 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 individual resistances.

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17
Q

If two 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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18
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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19
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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20
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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21
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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22
Q

Why is it advantageous to connect lamps in parallel?

A

If one lamp blows, the rest will be unaffected and can still receive current (i.e. the circuit is still complete).

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23
Q

Is mains electricity an a.c supply or a d.c supply? What do each of these stand for?

A

Mains electricity is an a.c supply

a.c. : Alternating Current
d.c. : Direct Current

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24
Q

Define alternating current and direct current.

A
  • Alternating current: Current that continuously changes direction at a specific frequency
  • Direct current: One directional current flow
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25
Q

What is the frequency and voltage of the UK mains electricity supply?

A
  • Frequency: 50 Hz
  • Voltage: 230V
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26
Q

How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires.

A
  1. Live wire
  2. Neutral wire
  3. Earth wire
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27
Q

State the insulation colour used on the Earth wire.

A

Green and Yellow Stripes

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28
Q

State the insulation colour used on the live wire.

A

Brown

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29
Q

State the insulation colour used on the Earth wire.

A

Blue

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30
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 (such as a surge or the casing becoming live), current will flow to the ground
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31
Q

What potential is the neutral wire at?

A

0 Volts

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32
Q

State the potential difference between the live and earth wires.

A

230 Volts

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33
Q

What is the purpose of the neutral wire?

A

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

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34
Q

For metal appliances, where is the Earth wire connected to? Why?

A
  • Earth wire is connected to the metal casing
    of the appliance
  • If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution
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35
Q

State two equations for the power of a circuit. Give appropriate units.

A

P = IV P = I2 R

Power (Watts), Current (Amperes)
Potential Difference (Volts), Resistance (Ohms)

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36
Q

State an equation linking energy transferred, power and time. Give appropriate units.

A

E = Pt
Energy (Joules), Power (Watts), Time (Seconds)

37
Q

State an equation linking energy transferred, power and time. Give appropriate units.

A

E= QV
Energy (Joules), Charge (Coulombs), Potential Difference (Volts)

38
Q

What 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
39
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
40
Q

Describe the energy transfers in a battery 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
41
Q

What three things 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
41
Q

What are the two types of transformers used in the National Grid?

A
  1. Step-Up Transformers
  2. Step-Down Transformers
42
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.

43
Q

Where are step-up transformers found in the National Grid? What do they do?

A
  • Step-Up Transformers are used when connecting power stations to transmission cables
  • They increase the potential difference
44
Q

Where are step-down transformers found in the National Grid? What do they do?

A
  • Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)
  • They decrease the potential difference
45
Q

Why do transmission lines transfer electricity at high potentials?

A
  • A high potential, results in a low current
  • The lower the current, the less energy that is wasted as heat
  • Therefore it is more efficient
46
Q

What happens when two electrically charged objects are brought close together?

A

They exert a force on each other.

46
Q

What can happen when insulating materials are rubbed together?

A

They can become (statically) electrically charged.

47
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
47
Q

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

A
  • Lower potentials are safer for domestic use and reduces the likelihood of
    severe electrocution
  • Appliances are designed for 230V
48
Q

What happens when two identically charged objects are brought close together?

A

They exert a repulsive force on each other and repel.

49
Q

What happens when two oppositely charged objects are brought close together?

A

They exert an attractive force on each other and attract.

50
Q

Give an example of a non-contact force.

A

The repulsive or attractive force acting between two electrically charged objects.

51
Q

What is an electric field?

A

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

52
Q

Where can electric fields be found?

A

Surrounding any charged object.

53
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
54
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.

55
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.

56
Q

Alternating Potential Difference:​

A

A continually oscillating current flow, which results in the potential difference across two points continually oscillating between a positive and negative value.

57
Q

Amperes (Amps):

A

​The unit of current.

58
Q

Attraction:

A

A force pulling two opposite charges together, when they are brought near each other.

59
Q

Coulomb:

A

The unit of charge.

60
Q

Diode:​

A

A component that only allows current to flow through in the forward direction. They have very large resistances in the reverse direction.

61
Q

Direct Potential Difference:

A

​A one-directional current flow.

62
Q

Earth Wire:

A

The green and yellow striped safety wire that prevents an appliance
from becoming live.

63
Q

Electrical Current:

A

The rate of flow of electrical charge. Its value is the same at any position in a single closed loop.

64
Q

Electrical Work:​

A

When charge flows in a circuit, electrical work is said to be done.

65
Q

Filament Lamp:

A

​A light emitting component consisting of an enclosed metal filament. Its resistance increases as the filament’s temperature increases.

66
Q

Insulation:​

A

The coating around power cables that prevents electrocution and is colour coded to allow for easy identification.

67
Q

Light Dependent Resistor (LDR):​

A

A light sensitive component whose resistance increases as its temperature decreases.

68
Q

Live Wire:​

A

The brown coloured wire that carries the alternating current from the supply in a mains power supply.

69
Q

Neutral Wire:

A

The blue coloured wire that completes the circuit in a mains power supply.

70
Q

Mains Electricity:​

A

An a.c supply, which in the UK has a frequency of 50Hz a value of 230V.

71
Q

Non-Contact Force:​

A

A force experienced between two separated objects. Examples include gravity, and magnetic and electric forces.

72
Q

Ohmic Conductor:​

A

A conductor whose current flow is directly proportional to the potential difference across it, when held at a constant temperature.

72
Q

Ohms:

A

The unit of resistance.

73
Q

Parallel:

A

Components connected in parallel have the same potential difference across each component. The total current is equal to the sum of the currents flowing through each component.

74
Q

Potential Difference:

A

The product of a component’s resistance and the magnitude of current flow through it.

75
Q

Repulsion:

A

​Caused when two like-charges are brought near each other.

76
Q

Resistance:

A

​A measure of the opposition to current flow.

77
Q

Resistors in Parallel:​

A

The total resistance is equal to the inverse of the sum of the inverses of the resistance of the parallel components. The total resistance of two parallel resistors is always less than the lowest individual resistor value.

78
Q

Resistors in Series:​

A

The total resistance is equal to the sum of the resistances of the individual components.

79
Q

Series:

A

Components connected in series have the same current passing through

80
Q

Step-Down Transformers:​

A

Devices found between the transmission cables and the consumer that lower the potential difference of the power so it is at safe, usable levels.

81
Q

Step-Up Transformers:

A

Devices that increase the potential difference generated by a power station, so that the electrical power transmitted along the transmission cables is at a higher potential.

82
Q

The National Grid:​

A

The network of power stations, transformers and cables that connect consumers to power stations.

83
Q

Thermistor:

A

A temperature dependent component, whose resistance increases as its temperature decreases.

84
Q

Volt:​

A

The unit of potential difference.

Physics AQA (4 decks)

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