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Physics > Topic 10 - Circuits > Flashcards

Topic 10 - Circuits Flashcards

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1
Q

What does AC mean?

A

Alternating current

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2
Q

What does DC mean?

A

Direct current

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3
Q

Is mains electricity AC or DC?

A

AC

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4
Q

What is meant by the frequency of a supply?

A

The rate at which an AC current changes

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5
Q

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

A 
Frequency = 50Hz
Voltage = 230V
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6
Q

What type of current do batteries and cells supply?

A

Direct current (DC

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7
Q

What is the power rating of an appliance?

A

It shows how much energy a device converts per second

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8
Q

What wires does a typical domestic appliance have?

A

Live wire
Neutral wire
Earth wire

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9
Q

What colour is the live wire?

A

Brown

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10
Q

What colour is the neutral wire?

A

Blue

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11
Q

What colour is the earth wire?

A

Green and yellow (striped)

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12
Q

Explain when the earth wire does and doesn’t carry a current

A

Under normal circumstances, no current flows through the earth wire
Current flows when a fault occurs in the appliance (such as a surge or the casing becoming live)

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13
Q

What potential is the neutral wire at?

A

0 volts

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14
Q

State the potential difference between the live and earth wires

A

230 volts

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15
Q

What is the purpose of the neutral wire?

A

The complete the circuit by connecting the appliance back to the mains supply

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16
Q

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

A

The metal casing of the appliance

If the live wire becomes touching the casing, the current will flow through the earth wire, preventing electrocution

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17
Q

How does a fuse stop a device from getting damaged?

A

When the current becomes too high the fuse wire will melt and break, therefore stopping current from flowing to the appliance and preventing damage

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18
Q

Why is it important to connect a fuse or switch to the live wire?

A

When the switch is turned off, or when the fuse breaks, it will break the circuit and stop current running through the wire. This provides a method to stop current flowing into the appliance

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19
Q

Why is it dangerous to have a connection between the earth wire and the live wire?

A

It can result in a current surge, causing electrical shocks

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20
Q

What factors affect the energy transferred when charge flows through a component?

A

Amount of charge

The potential difference across the component

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21
Q

How do you work out energy?

A

Current x potential difference x time

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22
Q

Define potential difference in terms of charge

A

The work done per unit charge

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23
Q

How to work out energy transferred

A

Charge x potential difference

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24
Q

When an electrical current flows through a resistor why does it heat up?

A

There are collisions between the electrons and the ions in the resistor’s lattice. This causes a transfer of kinetic energy into thermal energy which is released into the surroundings

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25
Q

How do low resistance wires reduce unwanted energy transfers?

A

A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating

26
Q

What are some advantages of the heating effect in resistors?

A

It is useful for appliances such as toasters or electrical fires, where the heat is the desired product

27
Q

What are some disadvantages of the heating effect in resistors?

A

The loss of energy as it can make an appliance inefficient

If an appliance overheats it can catch fire or overhear, which could ruin the device or injure the user

28
Q

What are the units of power?

A

Watts (W)

29
Q

Define power

A

The rate of energy transfer or the rate at which work is done

30
Q

How do you work out power (in circuit)?

A 
Current x potential difference
OR
Current^2 x resistance
OR
Energy/time
31
Q

How does resistance affect current in a circuit?

A

As the total resistance of a circuit increases, the current flowing through the circuit decreases

32
Q

How can’t he current in a circuit be varied?

A

Using a variable resistor

33
Q

How do you calculate potential difference?

A

Current x resistance

Energy transferred/charge

34
Q

How is total resistance affected by two resistors in series?

A

The total resistance is equal to the sum of the two resistors

35
Q

How is total resistance affected by two resistors in parallel?

A

The total resistance decreases; it is less than the resistance of the resistor with the lowest resistance

36
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

37
Q

List 4 components for which resistance is not constant as current changes

A

Filament lamps
Diodes
Thermistors
Light dependant resistors

38
Q

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

A

Resistance increases
Metal ions have more kinetic energy so vibrate more, colliding more frequently with electrons as they flow through the metal
This created more resistance to current flow

39
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

40
Q

State what happens to the resistor of a thermistor as temperature increases?

A

It decreases

41
Q

Give two examples of when a thermistor may be used

A

In a thermostat to turn a heater on below a certain temperature
In a freezer to turn on a cooler when the temperature becomes too high

42
Q

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

A

It increases

43
Q

Give an application for a LDR

A

Street lamps or night lights

44
Q

How do diodes work?

A

It only allows current to flow in one direction. If current is flowing the right way, the resistance is large for small voltages, but then at higher voltages becomes very small

45
Q

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

A

Series or parallel

46
Q

What is voltage also know as?

A

Potential difference

47
Q

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

A

In a series circuit the total potential difference is shared between each component
In a parallel circuit the potential difference across each component is the same

48
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

49
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

50
Q

Where must a voltmeter be placed in a circuit?

A

In parallel with the component that is being measured

51
Q

How can a volt be described?

A

Joule per coulomb

52
Q

What is an electric current?

A

The rate of flow of charge

53
Q

How to work out charge

A

Current x time

54
Q

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

A

Current is the same in all points in a closed loop

55
Q

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

A

Potential difference

Resistance

56
Q

What is an ammeter and where must it be connected in a circuit?

A

An ammeter measures current . It is placed in series with the component it is required to measure

57
Q

What happens when current reaches a junction in a circuit?

A

Current is conserved; the total current remains the same and is split between the two branches

58
Q

What three subatomic components make up an atom?

A

Electrons
Protons
Neutrons

59
Q

How is current defined?

A

The rate of flow of charge (or electrons) around a circuit

60
Q

What are the units of charge?

A

Coulombs (C)

Physics (12 decks)

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