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Physics Paper 1 > P2 - Electricity > Flashcards

P2 - Electricity Flashcards

1
Q

What is electric current?

A

The rate of flow of electrical charge.

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2
Q

In most circuits, what is the charge that flows to carry the current.

A

Electrons.

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3
Q

What is the word equation for flow of charge?

A

charge flow = current x time

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4
Q

What is the symbol equation for flow of charge?

A

Q = I t

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5
Q

At any point in a single closed loop, the current…

A

is the same.

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6
Q

The current through any component depends on…

A

the resistance (R) of the component and the potential difference (V) across it.

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7
Q

What is the definition of resistance?

A

The amount that a component or circuit opposed the flow of current.

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8
Q

What is the unit of resistance?

A

Ohms, Ω

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9
Q

What is the alternative term for potential difference, that means the same thing?

A

Voltage

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10
Q

What is voltage?

A

the pressure from an electrical circuit’s power source that pushes charged electrons (current)

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11
Q

What is the word equation for potential differnce?

A

potential difference = current x resistance

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12
Q

What is a series circuit?

A

A circuit where all the components are connected in one loop.

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13
Q

In a series circuit, what can be said about the current, potential difference and resistance?

A

The current is the same through each component. The total potential difference of the power supply is shared between the components. The total resistance is the sum of the individual resistances.

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14
Q

Why does adding resistors in parallel decrease the total resistance?

A

There are more routes for electrons to take between the branches, so it is easier for current to flow.

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15
Q

What is DC?

A

Direct Current (DC) is when current always flows in one direction. It is the current found in circuits powered by a cell or battery.

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16
Q

What is AC?

A

Alternating Current (AC) is when the direction of current flow rapidly changes, giving an alternating potential difference. It is how mains electricity is supplied in the UK.

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17
Q

What two word equations relate power, potential difference, current and resistance?

A

power = potential difference x current
power = (current)2 x resistance

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18
Q

What does the amount of energy an appliance transfers depend on?

A

The power of the appliance and how long it is switched on for.

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19
Q

What does work have to do with electric circuits?

A

Work is done when charge flows in a circuit.

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20
Q

What is the National Grid?

A

The National Grid is a system of cables and transformers linking power stations to consumers.

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21
Q

What is a transformer?

A

A device which alters the potential difference and current of electricity in the cables.

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22
Q

In the branches of a parallel circuit, what can be said about the current, potential difference?

A

The total current splits between the “branches” of the parallel circuit. The potential difference across each branch is the same.

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23
Q

Describe the current in a series circuit?

A

In a series circuit the current is the same as it only has one path to flow through.

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24
Q

How does potential difference vary across two components when connected in series and parallel?

A

In series the PD is shared between each component.
In parallel the PD across each branch is the same.

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25
Q

If two resistors are connected in parallel what can be said about their total resistance?

A

Their total resistance is less than the smallest of the two individual resistances.

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26
Q

How should you connect an ammeter in a circuit to measure current?

A

Ammeters should be connected in series with the component they are measuring the current of.

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27
Q

How should you connect a voltmeter in a circuit to measure PD?

A

Voltmeters should be connected in parallel to the component they are measuring PD of.

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28
Q

Why is it advantageous to connect lamps in parallel?

A

If one lamp blows the other ones will still be able to receive current.

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29
Q

What can happen when insulating materials are rubbed together?

A

They can become electrically charged.

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30
Q

What is the equation for voltage?

A

V = IR

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31
Q

What is different about current flow through a diode?

A

Current only flows in one direction because resistance is very high in the other direction so prevents current flow.

32
Q

Why can two insulating materials be electrically charged when rubbed together?

A

Electrons are transferred.
Material gaining electrons becomes negatively charged.
Material losing electrons becomes positively charged.

33
Q

What is a non-contact force?

A

The repulsive or attractive force acting between two charged objects.

34
Q

What is an electrical field?

A

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

35
Q

Describe the electrical field around a charged particle.

A

Strongest closest to the object.
Decreases in strength as you move further away.

36
Q

In situations where sparks are unwanted, what precautions must take place to prevent build up of static charge?

A

Any materials that are rubbing together must be earthed to allow the charge to flow off the materials.

37
Q

State two equations for the power of a circuit.

A

P = IV
P = I^2 R

38
Q

Give the equation for energy transferred. (power)

A

E = power x time

39
Q

What two main factors does the energy transferred by an appliance depend on?

A

Power of the appliance.
How long it is used for.

40
Q

What three things determine the power of a circuit?

A
  • Amount of energy that was transferred in a given time.
  • The current running through it.
  • The voltage across the circuit.
41
Q

What is the purpose of the National Grid?

A

To link power stations to consumers so they have access to a source of electricity.

42
Q

Two types of transformers used in the National Grid.

A

Step-up and step-down.

43
Q

What do step-up transformers do?

A

Increase the voltage so the current can decrease meaning less energy is wasted as heat energy.

44
Q

What do step-down transformers do?

A

Increase the current by decreasing the voltage.
This means that it is safer for domestic use.

45
Q

Where are step-up transformers found?

A

Connecting power stations to transmission cables.

46
Q

Where are step-down transformers found?

A

Connecting transmission cables to domestic buildings.

47
Q

Define alternating current.

A

Current that continuously changes direction, giving an alternating voltage.

48
Q

Define direct current.

A

One directional current flow.

49
Q

What are the wires called that connect the electrical appliances to the mains?

A
  • live
  • neutral
  • earth
50
Q

What is the purpose of the earth wire?

A

In the case of a fault, current will flow to the ground.

51
Q

What voltage is the neutral wire at?

A

0 volts.

52
Q

State the voltage between the live and the earth wires.

A

230 V

53
Q

What is the purpose of the neutral wire?

A

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

54
Q

For metal appliances where is the earth wire connected to and why?

A

The metal casing of the appliance.
If the live wire becomes loose and touches the metal casing the current will flow through the earth wire, preventing electrocution.

55
Q

Explain how voltage works.

A

The voltage is the difference from the negative side of the battery, where there is an excess of electrons to the positive side of the battery, where there are less electrons.
It is the pressure from an electrical circuits power source that pushes current.

56
Q

What is the frequency of the AC mains supply in the UK?

A

50 Hz

57
Q

Equation that links energy transferred, charge flow and voltage.

A

Energy transferred = charge flow x voltage

58
Q

What is meant by a zero error on the display of an ammeter?

A

The ammeter displays a reading when not connected to the circuit.

59
Q

Define diode.

A

A diode is a device that allows current to flow in one direction but not in the reverse direction.

60
Q

Define voltage.

A

It is the pressure from an electrical circuits power source that pushes current.

61
Q

Where can you find DC?

A

Found in circuits powered by a cell or battery.

62
Q

Why do we use AC for the mains supply?

A

It’s better for transporting current over long-distances.

63
Q

What equation links energy transferred, charge and voltage?

A

Energy transferred = charge x voltage

64
Q

What does Ohms law state?

A

The voltage across a conductor is directly proportional to the current flowing through it, providing all physical conditions, such as temperature, remain constant.

65
Q

What is an ohmic conductor?

A

A conductor that obeys ohms law.

66
Q

How does resistance change in a filament lamp as voltage increases?

A

The current increases as the voltage increases, causing the temperature to increase, meaning the resistance increases.

67
Q

What does energy efficient mean?

A

A high proportion of the total energy / power input is usefully transferred.

68
Q

What happens to a LDR resistance as light-intensity increases?

A

The resistance decreases.

69
Q

What is a LDR?

A

Light dependent resistor, are used to detect light levels.

70
Q

For results to be precise, what do they need to be?

A

Close together in value.

71
Q

What is a thermistor?

A

Temperature sensors, their resistance decreases as temperature increases.

72
Q

Where are thermistors used?

A

Fire alarms - when high temperatures are detected, resistance decreases causing a sound to be generated.

73
Q

What is a diode?

A

A device that allows current to flow in one direction but not in the reverse direction.

74
Q

What is a variable resistor?

A

Moving the position of the slider on this resistor, changes the resistance.

75
Q

Where are variable resistors used?

A

Some dimmer switches and volume controls.

Physics Paper 1 (4 decks)

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