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Physics LV > Electrical Circuits COPY - mock revision list > Flashcards

Electrical Circuits COPY - mock revision list Flashcards

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1
Q

What is an electric current

A

An electric current is a flow of electric charge

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2
Q

What do cells and batteries supply

A

Cells and batteries supply direct current (DC)

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3
Q

What is Direct current (D.C)

A

Current that always passes in the same direction

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4
Q

What is alternating current (A.C)

A

Current that is constantly changing direction

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5
Q

What type of supply is mains electricity

A 
Alternating current (A.C)
In the UK it has a frequency of 50 cycles per second (50Hz) and is about 230V
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6
Q

What can a diode be used for

A

A diode may be used for half wave rectification of a.c

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7
Q

Most electrical appliances are connected to the mains using………

A

A cable and a three pin plug

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8
Q

What are the colours of the different wires in a cable

A

Neutral wire = bLue (goes Left)
Live wire= bRown (goes Right)
Earth wire = green and yellow sTripes (goes to the Top

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9
Q

What is the case, cable grip and cable insulation of a three pin plug made of and why

A

The case is made of tough plastic or rubber, because these materials are good electrical insulators, and flexible too

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10
Q

What are the three pins from a three pin plug made from and why

A

The three pins are made from copper or brass, which are very good conductors of electricity

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11
Q

What happens if an electrical fault causes too great a current to flow

A

If an electrical fault causes to great a current to flow, the circuit is disconnected by a fuse or a circuit breaker in the live wire

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12
Q

What happens when the current in a fuse wire exceeds the rating of the fuse

A

It will melt, breaking the circuit

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13
Q

The thicker the wire in the fuse, …………

A

The higher the fuse’s rating .
This is because the thinner wire cannot take such a big load as the thicker one can; the thinner one will just melt at the same voltage and current that the thicker one would be able to take

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14
Q

What are some circuits protected by

A

Residual current circuit breakers (RCCBs)

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15
Q

Which is faster, a fuse or RCCBs

A

RCCBs operate much faster than a fuse

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16
Q

How do RCCBs operate

A

RCCBs operate by detecting a difference in the current between the live wire and the neutral wires

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17
Q

Appliances with metal cases are usually …….

A

Earthed

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18
Q

In what case would there be no need for an earth wire connection

A

If the appliances are double insulated

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19
Q

The ……………. And the ………. Together protect the wiring of a circuit

A

The EARTH WIRE and FUSE together protect the wiring of a circuit

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20
Q

What substances can electrical charges move easily through

A

Metals

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21
Q

What is the relationship between current, charge and time

A

current = charge / time

I = Q / t

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22
Q

What is the relationship between potential difference, energy transferred and charge

A

potential difference (or voltage) = energy transferred / charge

V = E / Q

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23
Q

What is a thermistor

A

A thermistor is a temperature - dependent resistor

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24
Q

Where do we use thermistors and light-dependent resistors

A

In sensor circuits

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25
Q

Whats an example of a use of a LDR

A

An LDR is used in a sensor circuit that switches an electrical light on and off.
For example, switching lights on when it gets dark

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26
Q

Whats an example of a use of a thermistor

A

A thermistor may be used in a thermostat to control temperature

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27
Q

What causes the resistance of a thermistor to decrease

A

The resistance decreases if its temperature increases

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28
Q

What causes the resistance of a LDR to decrease

A

The resistance decreases if the light intensity on it increases

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29
Q

How can you find the resistance of a component

A

The resistance of a component can be found by measuring the current through and potential difference across, the component

30
Q

What does the current through a component depend on

A

The current through a component depends on its resistance

31
Q

The greater the resistance, the ………… the current for a given potential difference across the component

A

The greater the resistance, the SMALLER the current for a given potential difference across the component

32
Q

What is the relationship between potential difference, current and resistance

A

potential difference = current x resistance

V = I x R

33
Q

The current through a resistor (at a constant temperature) is ……………………………… to the potential difference across the resistor

A

The current through a resistor (at a constant temperature) is DIRECTLY PROPORTIONAL to the potential difference across the resistor

34
Q

What are current-potential difference graphs used to show

A

Current-potential difference graphs are used to show how the current through a component varies with the potential difference across it

35
Q

What is the relationship between the resistance if a filament bulb and the temperature of the filament

A

The resistance of a filament bulb increases as the temperature of the filament increases

36
Q

Explain change in resistance in terms of ions and electrons

A

When an electrical charge flows through a resistor, some of the electrical energy is transferred to heat energy and the resistor gets hot.
This heat energy causes the ions in the resistor to vibrate more. The increase in movement of the ions makes it more difficult for the charge-bearing electrons to get through the resistor - the current can’t flow as easily and the resistance increases

37
Q

Why does the current through a diode flow in one direction only

A

As the diode has a very high resistance in the reverse direction

38
Q

What is the potential difference provided by cells connected in series equal to

A

The potential difference provided by cells connected in series is the sum of the potential difference of each cell (depending on the direction in which they are connected)

39
Q

What three things are true for components connected in series

A
  • the total resistance is the sum of the resistance of each component
  • there is the same current through each component
  • the total potential difference of the supply is shared between the components
40
Q

What two things are true for components connected in parallel

A
  • the potential difference across each component is the same

- the total current through the whole circuit is the sum of the currents through the separate components

41
Q

When does an LED emit light

A

An LED emits light when a current flows through it in the forward direction

42
Q

Why is the use of LEDs for lighting increasing

A

The use of LEDs for lighting is increasing because they use a much smaller current than other forms of lighting

43
Q

What happens to a resistor when electrical charge flows through it

A

When electrical charge flows through a resistor, the resistor gets hot

44
Q

What type of bulbs waste a lot of energy

A

A lot of energy is wasted in filament bulbs by heating

45
Q

What type of bulbs waste less energy

A

Less energy is wasted in power saving lamps such as Compact Fluorescent Lamps (CFLs)

46
Q

How to determine the period of an AC supply from an oscilloscope trace

A

The period of an AC supply is the time taken for one complete oscillation.
You can find this by looking at the time between one peak and the next, between one trough and the next, or between any two identical places on adjacent oscillations. (a bit like wavelength)

47
Q

How to determine the frequency of an AC supply from an oscilloscope trace

A

The frequency of an AC supply is the number of oscillations per second.
You can find it from the period:
Frequency = 1 ÷ period
Always remember to put the period into seconds before performing the calculation

48
Q

How do you determine the potential difference of an AC supply from an oscilloscope trace

A

The vertical height of the AC trace at any point shows the input voltage at that point.
By measuring the height of the trace you can find out the potential difference of the AC supply

49
Q

How do you determine the potential difference of a DC supply from an oscilloscope trace

A

The voltage is the distance from the straight line trace to the centre line

50
Q

What is the power

A

The rate at which energy is transferred by an appliance

51
Q

What is the relationship between power, energy transferred and time

A 
Power = energy transferred / time
P = E / t
52
Q

What is the relationship between power, current and potential difference

A 
Power = current x potential difference
P = I x V
53
Q

What is resistance measured in

A

Ohms, Ω

54
Q

How should you determine the size of the fuse needed

A

The fuse should be rated at a slightly higher current than the device needs.
e.g If the device works at 3 A, use a 5 A fuse

55
Q

What is the relationship between energy transferred, potential difference and charge

A

Energy transferred = potential difference x charge

E = V x Q

56
Q

What are examples of electrical appliances that bring about energy transfers

A

Many electrical appliances used at home are lamps or heaters.
In a lamp, electrical energy is transferred as light and heat.
In a toaster, electrical energy is transferred as heat.
In a hair dryer, electrical energy is transferred to kinetic energy, heat energy, and sound energy

57
Q

What does the amount of energy an appliance transfers depend on

A

The amount of energy an appliance transfers depends on how long the appliance is switched on for and its power

58
Q

What is the relationship between energy transferred from the mains, power and time

A

Energy transferred from the mains = power x time

E = p x t

59
Q

What is a kilowatt-hour

A

A kilowatt-hour is the amount of electrical energy used buy a 1 kW appliance left on for 1 hour

60
Q

What is the no. of units (kWh) used equal to

A

No. of UNITS (kWh) used = POWER (in kW) x TIME (in hours)

61
Q

What is the cost (of electricity) equal to

A

COST = no. of UNITS x PRICE per unit

62
Q

Reading electricity meters

A

If you look at a domestic electricity bill for a 3 month period, you will see that there are two meter readings. One is the present reading and the other is the previous (last) reading.
Subtracting the previous reading from the present reading gives the number of units used in that 3 month period.
Electricity is priced in pence per unit.
Multiplying the number of units used by the price per unit
gives the cost of electricity for that period.

63
Q

What is electricity distributed from power stations to consumers along

A

Electricity is distributed from power stations to consumers along the National Grid

64
Q

What are the essential parts of the national grid

A

Power station –> Step-up transformer –> Step-down transformer –> Consumers

65
Q

For a given power, increasing the voltage …….. the current required

A

For a given power, increasing the voltage REDUCES the current required

66
Q

Why is it better to have a high voltage rather than a high current (in order to get the huge amount of power needed by consumers)

A

The problem with a high current is that you lose lots if energy through heat in the cables.
Keeping the current very low, means less wasted energy because the heating of the of the cables is reduced.
THIS REDUCES THE ENERGY LOSSES IN THE CABLES

67
Q

What is a transformer

A

A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply.

68
Q

What is a step-up transformer

A

A transformer that increases the voltage

69
Q

What is a step-down transformer

A

A transformer that decreases the voltage

70
Q

Why do we have transformers as part of the national grid

A

The transformers habe to step the voltage up at one end, for efficient transmission, and then bring it back down to safe, usable levels at the other end

Physics LV (11 decks)

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