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LSS > Electrical Systems > Flashcards

Electrical Systems Flashcards

1
Q

what is electricity

A

electricity is a form of energy that is caused by the flow of electric charges

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2
Q

what is needed for electricity to flow through a circuit

A

a source of electrical energy and a closed circuit

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3
Q

what is a short circuit and why do they happen

A

a short circuit is an unintentional bypass in the circuit, resulting in a very large current from the electrical source which can generate enough heat to start a fire. current flows through a path of minimal resistance instead hence no current flows through the light bulb

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4
Q

define electrical current (I)

A

an electrical current is the rate at which electric charge flows. it is a measure of the amount of charge passing any point per second.

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5
Q

what is the S.I. unit of electrical current and what is it written as?

A

ampere
A

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6
Q

define a conventional current

A

it is when current flows from the positive terminal to the negative terminal in a closed circuit

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7
Q

is the direction of convential current flow different from or the same as that of electron flow? why

A

different
electrons flow from the negative terminal to the positive terminal

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8
Q

what is used to measure electrical current. how is it connected to the circuit?

A

ammeter
it is connected in series with the positive terminal of the ammeter connected to the positive terminal of the cell

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9
Q

how should an ammeter be read?

A

to the nearest half of the smallest division (to 1dp)

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10
Q

define potential difference (v)

A

the potential difference between two points in an electric circuit is the amount of energy needed to move a unit charge from one point to another

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11
Q

what is the s.i. unit of potential difference? what is written as

A

volt
V

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12
Q

does the resistance in the circuit affect potential difference?

A

no. an electric cell establishes a fixed potential difference across its ends regardless of the resistance in the circuit. only the current drawn from the battery changes with resistance, not its potential difference.

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13
Q

what is used to measure potential difference? how should it be connected to the circuit?

A

voltmeter
it must be connected in parallel to the component for potential difference to be measured. the positive terminal of the voltmeter should be connected to the positive terminal of the cell.

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14
Q

what happens if a voltmeter is connected in series?

A

it would cause an open circuit as the voltmeter does not allow any electrical current to pass through it.

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15
Q

how should a voltmeter be read?

A

to the nearest half of the smallest division (2dp)

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16
Q

define resistance (R)

A

the electrical resistance of a component is a measure of how much the component opposes the flow of electric current

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17
Q

how are the resistance of a component (R), the potential difference across a component (V) and the current flowing through a component (I) related

A

V=IR

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18
Q

what is the s.i. unit of resistance? how is it written?

A

ohm
Ω

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19
Q

what are the factors affecting resistance?

A

the cross-sectional area of a wire (the wider the wire, the lesser the resistance to the flow of electrical charge)

the length of a wire (the longer the wire, the higher the frequency of collisions between the free moving electrons and atoms of the wire -> greater resistance)

the material of the wire (wires made of nichrome have a higher resistance than copper wires of the same length and cross-sectional area)

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20
Q

what is a resistor

A

it is a conductor in a circuit that is used to control the size of the current flowing in a circuit

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21
Q

what is the difference between a fixed resistor and a variable resistor (rheostat)

A

a fixed resistor has a resistance of fixed value, while a variable resistor (rheostat) has a resistance that can be varied, it is used to vary the amount of current flowing in a circuit.

22
Q

what happens when additional resistors are added in parallel to the circuit?

A

the total effective resistance in the circuit decreases and the total current drawn from the cell increases.

23
Q

if the resistors are replaced by lamps, how will their brightness be affected if more lamps are connected in parallel?

A

the brightness of the lamps will remain the same.
more current is drawn from the cell to make the additional lamp light up with the same brightness. total current increases but the current in each branch remains the same.

24
Q

explain the heating affect of an electric current

A

when electrical charges flow through a wire, they lose some of their energy to the particles in the wire. this causes the particles to vibrate more vigorously. hence, the wire becomes hotter.

25
Q

give an example of a material used in heatings appliances

A

nichrome as it has a high resistance

26
Q

explain the lightning effect of an electric current

A

sometimes, the heating effect of a current can lead to a lighting effect.

27
Q

give an example of the heating effect leading to the lighting effect

A

the coiled filament in a traditional light bulb. as current flows through the filament, it heats up and glows to give out light.

28
Q

what are the factors affecting the magnetic effect?

A

the number of turns of coil, the current through the coil (the number of cells) and inserting a soft iron coil into the coil.

29
Q

explain the chemical effect of an electric current (extraction of metals)

A

electricity can be used to break down compounds into its elements. electrolysis can be used to obtain reactive metals like sodium and aluminium.

30
Q

explain the chemical effect of an electric current (electroplating)

A

electroplating is the process of depositing a layer of metal on another substance using electrolysis.

31
Q

explain the chemical effect of an electrical circuit (charging batteries)

A

rechargeable batteries make use of the chemical effect of the electrical current during charging. the charging current causes the electrical energy to be converted into chemical potential energy which is stored in the battery. the chemical potential energy is converted back into electrical energy when the batteries are being used.

32
Q

define power

A

power is the amount of energy transferred or converted per unit time. it is the rate of energy transfer/conversion.

33
Q

what is the s.i. unit of power? what is it written as?

A

watt
W

34
Q

what is the relationship between power (W), energy transferred/converted (J) and time taken (S)?

A

J=WS

35
Q

what is the formula for calculating electrical energy consumption?

A

energy (kWh) = power (kW) x time (h)

36
Q

what is the importance of reducing energy waste?

A

to conserve natural resources, reduce power plante emissions which results in cleaner air and water quality, protect ecosystems from destruction, and contribute to a healthier and happier world

37
Q

what are some ways to conserve energy in households?

A

buy electrical appliances that have energy labels with three or more ticks, switch off the air conditioner after a short while and then switch to a fan, switch off the water neater after use, use a vacuum flask instead of an electric hot water dispenser, and switch off the power socket to reduce standby power.

38
Q

how are electrical fires created?

A

large currents can be drawn when electrical circuits are damaged, do not work properly, or are misused. the large current generates heat, which mah melt the insulation and even cause a fire.

39
Q

what other hazards (apart from electrical fires) can large currents cause?

A

large currents are dangerous when they pass through a person’s body. when this happens, he or she will experience an electric shock or electrocution which usually results in serious injury or death. this can happen in appliances with metal casing or metallic parts on the outside.

40
Q

what are the precautions that can be taken to prevent electrical hazards?

A
  • switch off and pull out the plug from the socket before cleaning electrical appliances
  • electrical appliances should be kept in dry places and handled with dry hands
  • call the electrician to repair damaged appliances or electrical cables as the wires inside may be exposed
  • never overload or insert any item into an electrical socket
41
Q

what are the safety features found in electrical circuits?

A

fuse and circuit breakers

42
Q

how does a fuse deal with large currents?

A

it makes use of the heating effect of an electric current to switch off the appliance in the event of large current flow.

43
Q

what is the current rating of a fuse?

A

it indicates the maximum amount of current that can flow through the fuse before the wire inside melts

44
Q

where can fuses be found?

A

they can be found in three pin plugs which are commonly used in household appliances

45
Q

what causes a fuse to blow?

A

any excessive current passing through the fuse can cause the wire inside it to melt. when this happens, we say that the fuse is “blown”

46
Q

what should one do with a “blown” fuse?

A

a “blown” fuse would need to be replaced after an electrical fault has been rectified

47
Q

how do circuit breakers deal with large currents?

A

when there is excessive current flow, the circuit breaker would turn off or “trip”

48
Q

where can circuit breakers be found?

A

consumer unit

49
Q

what happens when current flow is too large due to a faulty appliance?

A

the switch connected to the appliance trips and cuts off the current which prevents electrical shocks or fires

50
Q

what happens after a circuit breaker trips?

A

after the damaged appliance is fixed, the circuit can just be switched on again using the circuit breaker which does not need to be replaced

51
Q

what can happen if one does not have a circuit breaker ar home?

A

a surge of current can damage home appliances or even cause a fire

LSS (1 decks)

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