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CGP Physics > Section 2 - Electricity P1 (also have physical circuit flashcards) > Flashcards

Section 2 - Electricity P1 (also have physical circuit flashcards)

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1
Q

Define current:

A

Current is the rate of flow of charge round the circuit

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2
Q

What is the unit for current?

A

ampere (amp)

A

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3
Q

What carries the charge in a circuit?

A

Electrons usually carry the charge

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4
Q

Define voltage:

A

Voltage is what drives the current round the circuit.

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5
Q

What is another word for voltage?

A

Potential difference

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6
Q

What is the unit for volts?

A

volt

V

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7
Q

Define resistance:

A

Resistance is anything in the circuit which slows the flow down

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8
Q

What do components do to the resistance of a circuit?

A

The more components in a circuit the higher overall resistance there will be

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9
Q

What does current need to flow?

A

Current will only flow through a circuit if there is a voltage across it

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10
Q

What is the unit for resistance?

A

ohm

Ω

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11
Q

What is the relationship between current and voltage?

A

If you increase the voltage, then more current will flow

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12
Q

What is the relationship between current and resistance?

A

If you increase the resistance, then less current will flow

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13
Q

What is an ammeter? And where is it put in a circuit?

A

Ammeter measures current flowing through a component

Must be placed in series

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14
Q

What is an voltmeter? And where is it put in a circuit?

A

Voltmeter measures the voltage flowing through a component

Must be placed in parallel around a component, not around a variable resistor or battery

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15
Q

How would you set up apparatus for current-voltage graphs?

A
  • make a circuit with a component, ammeter and the variable resistor are all in series, with the voltmeter in parallel over the test component
  • as you vary the variable resistor. it varies the current
  • this allows you to take several pairs of readings
  • plot these values on a current(y)-voltage(x) graph
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16
Q

What is AC electricity supply? And what does AC mean?

A

AC (alternating current), is used for mains supply

AC - means the current is constantly changing direction

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17
Q

What is DC electricity supply? And what does DC mean?

A

DC (direct current) is used for battery supply

DC - means the current keeps flowing in the same directon

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18
Q

What is the UK mains electric supply in volts?

A

AC - 230 volts

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19
Q

What is the equation linking Current, Voltage and Resistance?

A

Voltage = Current x Resistance

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20
Q

Describe a graph of current against voltage for a circuit with a wire in:

A

The current through a wire (at a constant temperature) is proportional to voltage.

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21
Q

Describe a graph of current against voltage for a circuit with different resistors in:

A

The current through a resistor (at a constant temperature) is proportional to the voltage.
Different resistors have different resistances, hence they have different gradients of proportionality.

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22
Q

Describe a graph of current against voltage for a circuit with a metal filament lamp in:

A

As the temperature of the metal filament increases, the resistance increases (hence the elongated f shape)

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23
Q

Describe a graph of current against voltage for a circuit with a diode in:

A

Current will only flow through a diode in one direction.

So the graph will only increase in one quadrant

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24
Q

What does LED stand for?

A

Light-emitting diodes

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25
Q

What do Light-emitting diodes do?

A

They emit light when a current flows through them in the right direction

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26
Q

What are the practical applications of LEDs?

A
  • digital clocks
  • traffic lights
  • remote controls
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27
Q

What is the difference between an LED and a light bulb?

A

LEDs don’t have a filament that can burn out, light bulbs do

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28
Q

What is the general purpose of LEDs or light bulbs in a circuit?

A

They indicate the presence of of current in a circuit.

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29
Q

What is a LDR?

A

Light Dependent Resistor

-a resistor which changes its resistance depending on how much light falls on it

30
Q

In bright light what is the resistance like in a LDR?

A
  • the resistance is highest in bright light

- the resistance is lowest in darkness

31
Q

What are the uses of a Light Dependent Resistor?

A

Useful device for various electronic circuits

Burglar Detectors

32
Q

What is a thermistor?

A

a thermistor is a temperature dependant resistor

33
Q

In hot conditions what is the resistance like in a thermistor?

A
  • the resistance drops in hot conditions

- the resistance rises in cold conditions

34
Q

What are the uses of a thermistor?

A

Make useful temperature detectors

  • car engine temperature sensors
  • thermostats
  • fire alarms
35
Q

What is an example of a series circuit?

in use in life

A

Fairy lights

36
Q

What is a series circuit?

A

When all components are connected in one single loop between the +ve and -ve of the power supply (except for voltmeters)
-if you remove one component the whole circuit will stop working

37
Q

In a series circuit, what happens to the potential difference when you add more cells?
What are the rules about potential difference in a series circuit?

A

The potential difference (voltage) increases when you add more cells to a series circuit

  • potential difference is shared between all components
  • potential difference for each component depends on its resistance
38
Q

In a series circuit, what are the rules about current?

A
  • current is the same everywhere

- the size of the current depends on the total potential difference and the total resistance of the circuit (I=V÷R)

39
Q

In the series circuit, what are the rules about resistance?

A
  • the total resistance depends on the number and type of components present in the circuit
  • total resistance = the sum of the resistance of each component in the circuit
40
Q

What is a parallel circuit?

A

When each component is separately connected to the +ve and -ve of the power supply
-if you remove 1 component it will hardly effect the rest

41
Q

What is an example of a parallel circuit?

in use in life

A
  • most things connected in cars
  • household electrics
  • light switches in your house, each are on branches of a parallel circuit
42
Q

Are common everyday circuits parallel or series?

A

Normally contain a mixture of series and parallel parts

43
Q

In a parallel circuit, what are the rules for potential difference?

A

The potential difference is the same across all the branches

44
Q

In a parallel circuit, what are the rules for current?

A
  • current is shared between the branches
  • total current = total of all the currents through separate components
  • in parallel circuit junctions, the total current in = the total current out
  • the current through a branch depends on the resistance of the branch (higher resistance = lower current)
45
Q

In a parallel circuit, what are the rules for resistance?

A

-the total resistance of a circuit decreases if you add a second resistor in parallel

46
Q

What is the equation linking current, charge and time?

A

Q = I x t
Q - charge [unit = C (coulomb)]
I - current [unit = A]
t - time [unit = seconds]

47
Q

What is the relationship between charge and voltage?

A

The bigger the change in voltage, the more energy is transferred for a given amount of charge passing through the circuit.
-a battery with a bigger voltage will supply more energy per coulomb of charge which flows round
VOLTAGE IS THE ENERGY TRANSFERRED PER UNIT CHARGE PASSED

48
Q

One volt =

A

one joule per coulomb

49
Q

What is the equation linking voltage, energy transferred and charge?

A

energy transferred = charge x voltage

50
Q

What is the equation linking resistance, energy transferred, charge and current?

A

energy transferred = charge x current x resistance

51
Q

What are the three wires in a plug?

A

live
neutral
earth

52
Q

What wires are needed in a plug?

A

The live and neutral wires

-if something goes wrong,the earth wire there for safety

53
Q

What is the colour and features of the live wire?

A

colour: brown
- alternates between a high +ve and -ve voltage of about 230V
- electricity normally flows in through this wire

54
Q

What is the colour and features of the neutral wire?

A

colour: blue
- is always at 0V
- electricity normally flows out through the neutral wire

55
Q

What is the colour and features of the earth wire?

A

colour: green & yellow

- works with fuse or a circuit breaker for safety

56
Q

What is the safety precaution for appliances with a metal casing?

A
  • being ‘earthed’,to reduced the danger of electric shock

- the case must be attached to an earth wire, an earthed conductor can never become live

57
Q

What is the name for an appliance with a plastic casing? And why do appliances with plastic casings not need extra precautions?

A

double insulated

-plastic is an insulator so you can’t get a shock so an earth wire isn’t needed

58
Q

What does an earth wire and fuse or circuit breaker do if a fault develops in which the live wire touches a metal casing?

A
  • the case is earthed
  • a big current flows in through the live wire, through the case and out down the earth wire
  • the surge in current melts the fuse (or trips the circuit breaker), which cuts of the live supply
59
Q

What does the fuse melting or the circuit breaker tripping do?

A
  • it isolates the whole appliance, making it impossible to get an electric shock from the case
  • prevents the risk of fire by the heating effect of a large current
60
Q

What are circuit breakers?

A

An electrical safety device used in some circuits

-they protect the circuit from damage if too much current flows (like fuses)

61
Q

How do circuit breakers work?

A
  • they detect a surge in current of a circuit
  • they break the circuit by opening a switch
  • they can be reset by flicking a switch on the device
62
Q

What is the advantage of a circuit breaker over a fuse?

A

CIRCUIT BREAKER MORE CONVENIENT THAN FUSE
-circuit breakers need a switch flicked to reset them
-fuse needs to be replaced once it has melted
OPERATE MUCH FASTER THAN FUSES (SAFETY)
-circuit breakers break the circuit straight away
-fuse waste time, waiting to melt
RCCBs ARE BETTER @ PREVENTING ELECTROCUTION
-RCCBs work for small current changes
-the current might not be enough to melt a fuse

63
Q

What is a common type of circuit breaker?

A

Residual Current Circuit Breaker (RCCB)

64
Q

What does a RCCB do?

A

Normally the same current flows through live & neutral

  • if someone touches the live then this means the current will flow through them to earth, so the neutral wire carries less current than the live
  • RCCBs detect this difference in power and cuts of the power by opening a switch
65
Q

When there is an electric current in a resistor, what energy transfer is there?
And why does this occur?

A

an energy transfer which heats the resistor
-because the electrons collide with the ions in the lattice that makes up the resistor, this gives the ions energy which causes them to vibrate and heat up

66
Q

What can the heating effect of a resistor do?

A

Cause components in a circuit to break

  • causing circuits stop working or not work properly
  • fuses use this effect to melt and break the circuit
67
Q

What are the uses of a resistor?

A
  • for fuses to melt

- toaster (contain coils of high resistance wire, as the temperature increases it gives of infrared radiation)

68
Q

What is electrical power?

A

The rate at which an appliance transfers energy.

power (watts) = joules per second

69
Q

What is the equation linking electrical power, voltage and current?

A

P = I x V
P - Electrical power [unit = watts(W)]
I - Current
V - Voltage

70
Q

What is the equation linking current, time. energy transferred and voltage?

A

Energy transferred = current x voltage x time

CGP Physics (16 decks)

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