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physics > Electricty > Flashcards

Electricty Flashcards

1
Q

Describe the main four components of how mains electricity is set up in your home

A

underground cable, electric meter, fuse box, ring circuit

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2
Q

What are the three wires In a ring main circuit and their colours

A

Earth wire- green yellow
Neutral wire- blue
live wire- brown

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3
Q

Describe the functions of the live, neutral and earth wire

A

Live wire: provides a path for the electric current from the power station to travel through to the appliance
Neutral wire: completes the circuit by connecting it back to the power station
Earth wire: contains no current with low resistance in order to allow electric current to pass through to the earth in order to protect the user from an electric shock from a fault in the wire

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4
Q

What is the voltage of mains electricity supplied to homes in the UK

A

Between 220V to 240V

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5
Q

Why does current surge through the earth wire?

A

Because it has low resistance

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6
Q

What material are the pins in a plug made of and why

A

Metal brass because good insulator

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7
Q

In What two ways does a fuse help with safety

A

Prevents an electrical fire
Protects the user from an electric shock

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8
Q

Explain how a fuse prevents a user from an electric shock

A

1) contains a thing piece of metal wire with a low melting point
2) when the current exceeds a certain value the fuse becomes hot and melts so it “blows”
3) the circuit is now incomplete so current can not pass through it

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9
Q

What are the characteristics of a suitable fuse

A

1) should allow the current to pass through it
2) but should blow if the current gets slightly larger

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10
Q

Name three safety devices that can be present in a circuit apart form the earth wire

A

Fuse
Circuit breaker
Trip switch

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11
Q

Explain how the earth wire acts as a safety feature

A

When a person comes into contact with a faulty live wire, the live wire touches the metal casing
Where a large current surges through the low resistance path of the earth wire to the earth
This large current causes the fuse to blow which cuts the circuit off

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12
Q

What is double insulation, and how does it change the wires needed in a plug

A

When all electrical appliances are cased by an insulator so that they can not be touched by the user. The earth wire is not needed then

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13
Q

Which wire should the switch always be connected to and why

A

The live wire so that even if the circuit is open, electrical energy will not be able to pass through to the faulty appliance and the use will not get a shock

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14
Q

How are the wires in heating appliances such as a kettle designed

A

They have high resistance so that as current passes through them a large amount of heat energy is transferred to their surroundings

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15
Q

How does a filament bulb glow

A

A current is passed though the thin filament wire,
which has a high resistance,
So temperature increases (as a large amount of electrical energy is transferred into heat energy)
This heat is what causes it to glow

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16
Q

Definition of power

A

The rate at which electrical energy is transferred per second

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17
Q

Will a 50W bulb be dimmer or a 70W bulb be dimmer and explain why

A

50W will be dimmer as less electrical energy will be transferred per second

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18
Q

What is the equation for power

A

P= IV
Power= Current x Voltage
(Watts) = (Amps) x (Voltage)

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19
Q

What is another way that you can write the Energy/Power equation

A

E=PT
—) E=IVT

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20
Q

What is the equation for energy

A

E= PT
Energy= Power x Time
(Joules) = (Watts) x (Seconds)

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21
Q

What does A.C stand for

A

Alternating Current

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22
Q

Give an example of electricity using A.C and two examples for appliances giving D.C

A

A.C: Mains electricity
D.C: Batteries, Solar cells

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23
Q

How many electrons are in 1Coulomb?

A

6 x 10^18

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24
Q

What does it mean in terms of the movement of electrons if there is a net flow of charge

A

Electrons are moved from the negative terminal to the positive terminal

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25
Q

Describe the movement of electrons in a metal without any current or voltage supplied to it

A

The movement of electrons is random where an equal number of electrons are flowing in one direction that are flowing in the opposite direction

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26
Q

What is the equation for Charge

A

Q=IT
Charge= Current x Time
(Coulombs) = (Amps) x (Seconds)

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27
Q

Definition of current

A

The flow of electrical charge

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28
Q

Definition of voltage

A

The difference in electrical energy

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29
Q

If the voltage across a component is 6V, what is the energy it is supplying

A

6J per coulomb of charge

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30
Q

What is the equation for energy and charge

A

E = QV
Energy= Charge x Voltage
(Joules) = (Coulomb)(Volts)

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31
Q

Why are voltmeters not connected in series

A

Because they have a high resistance, so current would not be able to pass through and thus the voltage would not be able to be measured

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32
Q

Describe the resistance in a voltmeter and an ammeter

A

Voltmeter: high resistance
Ammeter: Low resistance

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33
Q

Describe what a voltmeter will measure if it is connected across a component, and then if it is connected across a cell or battery

A

If it is connected across a component, it will measure the electrical energy transferred to each coloumb of charge that PASSES through it, but if it is connected across a cell or battery it will measure the electrical energy transferred to EACH and EVERY coulomb of charge

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34
Q

Describe the current in a series circuit

A

The current is the same at all parts of the circuit

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35
Q

Describe the current in a parallel circuit

A

The current is divided by each branch, but the total current entering the cell is equal to the total current that leaves the circuit

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36
Q

Describe the potential difference in a series circuit

A

The potential difference is shared between each component

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37
Q

Describe the potential difference in a parralel circuit

A

The potential difference is the same across each branch and is equal to the total potential difference supplied by the cell

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38
Q

A 3V battery can supply a current of 5A for 20 mins before it need recharging.
State how much energy is transferred to battery per coloumb of charge and explain why

A

3J, because the voltage is equal to the energy transferred per coulomb of charge

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39
Q

What is the equation for calculating voltage(with resistance)

A

V=IR
(Voltage) = (Current)(Resistance)
volts= amps x ohms

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40
Q

On a graph plotted current (y axis) against voltage (x axis), if there is a steep gradient what does that mean

A

The resistance is low

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41
Q

Is a bulb an ohmic or non ohmic device

A

Non ohmic

42
Q

Describe what will happen to the appearance of a bulb when the resistance in the circuit is decreased

A

When resistance is decreased, current increases so the bulb will shine more brightly

43
Q

When a variable resistor is used in a circuit with a bulb in it, to change how much current passes through, what is the resistor acting as

A

As a dimmer switch

44
Q

What does a variable resistor do in a circuit containing an electric motor

A

Controls the speed of the motor

45
Q

Give two appliances that use LDRs

A

Cameras, burglar alarms

46
Q

Give two appliances that use a thermistor

A

Fridge, computer

47
Q

When is it important to use a thermistor

A

When the temperature needs to be maintained

48
Q

Describe how the resistance changes in a thermistor when the temperature is increased

A

When temperature increases, the resistance decreases (to allow current to flow to activate systems)

49
Q

Describe the changes in the resistance when the light intensity decreases in an LDR

A

Resistance increases when the light intensity increases

50
Q

What is the role of a diode

A

It allows current to flow through it in one direction

51
Q

Describe the name LED

A

They are diodes which glow when current passes through them

52
Q

Which circuits are diodes used in

A

Used in circuits with rectifier units(which convert alternating current into direct current)

53
Q

What happens when a diode is connected in the opposite direction to the flow of charge

A

The resistance increases so current is unable to flow through the circuit

54
Q

Explain why voltage is not directly proportional to current in a filament bulb

A

As voltage increases, energy provided to ATOMS IN THE FILAMENT BULB increases so they vibrate more
But as they vibrate more, the electrons carrying charges have more collisions with the atoms in the wire so the resistance increases
This makes it more difficult for the charges to flow thus current decreases

55
Q

Difference between static electricity and current

A

Static electricity is charge that has build up and does not move, but current is the flow of charge which does move

56
Q

Describe what the rubbing action of a rod to a cloth does in terms of charge

A

Negative electrons are TRANSFERRED from the rod onto the cloth
So the rod becomes positively charge and the rod becomes negatively charged

57
Q

what is earthing?

A

When a path is provided for charges to escape

58
Q

Describe how you could test if a metal nail was charged and then how you could test if a plastic rod was charged

A

Place the metal nail in a circuit with a bulb and if the bulb lights up then then it is charged

And then you can place the plastic rod near paper and if it attracts then it is charged

59
Q

Explain how a charged object like a balloon rubbed against a wall can attract to an object that is neutral

A

The charged object will be negatively charged
so when it is placed near the wall the negatively charged electrons form the wall will repel because like charges repel
So the wall becomes positively charged
And opposite charges attract

60
Q

What are induced charges

A

Charges that redistribute again once charged objects are moved away from them

61
Q

Explain how an inkjet projector works

A

Ink is fired from a nozzle and each drop of ink is negatively charged
the deflecting plates change the direction of the ink drop to change by electrostatic forces of attraction
The charges on the deflecting plates change hundreds of times until the ink drops are directed to where they need to be

62
Q

Suggest why a cable that has three wires might need to be thicker than a cable that has two wires

A

Because that cable might carry a higher current

63
Q

Suggest how you can keep the temperature of a wire constant during an experiment

A

Switch the circuit off during readings

64
Q

Why is a LED more efficient than a Filament bulb

A

Because it wastes less energy and it produces less heat

65
Q

What happens when you add more components to a series circuit

A

The resistance increases

66
Q

Two bulbs are connected in a parallel circuit. One bulb is unscrewed, what happens to the other bulb?

A

It’s brightness does not change

67
Q

The combined resistance of two resistors connected in series is 55 Ω. One of the series resistors is 30 Ω. What is the size of the second resistor?

A

25 ohms

68
Q

A parallel circuit has two identical resistors. A current of 4 A flows from the battery. What is the value of the current through each resistor?

A

2A

69
Q

A series circuit has two identical resistors. A current of 4 A flows from the battery. What is the value of the current through each resistor?

A

4A

70
Q

Two resistors are connected in parallel. The voltage across one of the resistors is 12 V. What is the voltage across the second resistor?

A

12V
(Resistors in a parralel circuit all have same voltage, but have different current because there is more paths for current to travel through)

71
Q

Outline a method that you can use to produce a graph of current against voltage

A

Set a variable resistor at a high value
Measure the current and voltage from the ammeter and voltmeter
Decrease the value on the variable resistor and decrease it each time in equal amounts for every value
Repeat the experiment to calculate an average

72
Q

What happens to the resistance in a parralel circuit when you add more resistors

A

The total resistance decreases because each branch provides more current to flow

73
Q

Why is the resistance of a longer wire greater than that of a shorter wire

A

Because electrons collide with more atoms

74
Q

What are two limitations of the experiment where you change the length of a wire to investigate the resistance and how can they be avoided or resolved?

A

1) Zero error,
Can subtract the zero error from final value
2)heating effects from resistance
Can be avoided by switching the circuit off between readings

75
Q

Suggest and of four safety hazards that can be present in a kitchen and what they can do

A

1) misusing equipment, like placing a metal fork in a toaster can cause an electric shock
2) water appliance coming into contact with an electrical appliance can cause an electric shock because water conducts electricity (like a washing machine)
3)overloading cables increases the current and can overheat and create a fire
4)Some heating appliances may reach very high temperatures and may cause burns

76
Q

What are three reasons to use a circuit breaker instead of a fuse

A

1) can be reused
2) work instantly
3) do not require an earth wire

77
Q

Explain how a photocopier works in terms of charges

A

1)paper is placed down and light reflects the light parts and the dark parts
2) the drum is positively charged by the corona wire
3)paper is on the drum so the light parts conduct electricity but the dark parts do not conduct electricity so they remain positively charged
4)the toner is negatively charged so it is attracted to the shadow
5)the fresh sheet of paper has more positive charge than the toner so it attracts the charges, so the paper picks up the pattern of the carbon powder
6)this is then fixed in place by a heater

78
Q

Why is water deflected when a charged rod is placed near it?

A

Because the water molecules and the charged rod have opposite charges so opposite charges attract

(Water is a polar molecule which means that one side is postively charged and the other negatively charged. A charged rod can attact one side of the water molecule. )

79
Q

Name three good conducting materials of electricity

A

1)Copper
2) Aluminum
3)Silver

80
Q

Why are many appliances fitted with a fuse

A

To prevent overheating

81
Q

Why are charges able to flow though Metals but not through plastic

A

Because Metals have a large amount of delocalized electrons (free charge carriers) but plastic does not

82
Q

If the current in a heater is 3A, calculate the charge that flows through it in 10minutes

A

(600 x 3)
1800C

83
Q

What is the difference between a complete circuit and an incomplete circuit

A

A Complete circuit has no gaps so charges can flow all the way around, but an incomplete circuit has gaps so charges can not flow all the way around

84
Q

Why would it not be a good idea to connect all the parts of an electric cooker in series

A

Because if one part of the electric cooker is turned on, all the other parts are also turned on

85
Q

Is the voltage directly proportional to the resistance

A

No
(Voltage is directly proportional to current assuming resistance stays the same because resistance is a physical property of a wire)

86
Q

Describe the relationship between current and voltage in a wire

A

The current is directly proportional to the voltage, provided that the temperature stays the same

87
Q

Explain the I-V graph for a piece of wire, a filament bulb, diode

A

Piece of wire: resistance remains constant because straight line through origin
Filament bulb: as current increases resistance also increases because gradient of line is becoming less steep
Diode: low in one direction when current is high, but resistance is high in the other direction when current is low

88
Q

What are 4 factors that affect resistance of a wire

A

1)length
2)thickness
3) material
4jtemperature

89
Q

What is another way that energy can be expressed?

A

In Joules per second

90
Q

Why does charge never build up on conducting materials?

A

-electrons are able to move freely so just move back onto the material when being rubbed

91
Q

explain why electrostatic charges can be dangerous when fuelling an aerorplane

A

A spark can build up which is transferred to the earth
And can create an explosion

92
Q

How can a fuse protect a circuit

A

It prevents it from overheating

93
Q

in which direction does current flow

A

from positive to negative terminal

94
Q

explain what happens in a filament lamp when the current increases

A

-When current increases, the _temperature also increases because more collisions of electrons with the atoms in the wire, producing more thermal energy
-when temperature increases, resistance increases because the atoms in the wire begin to vibrate faster so more difficult for electrons to pass, therefore less current is able to pass

95
Q

give an example of where variable resistors are used and explain how

A

used in dimmer switches
when resistance is low, current is high, so the light is brighter,
when resistance is high, current is low so light is dimmer

96
Q

where can lars be used and where can thermistors be used

A

LDRS used in burglar alarms
thermistors used in fire alarms

97
Q

give the advantages and disadvantages of both series and parallel circuits
t

A

series advantages; -all components can be controlled by a single switch
-few wires required
disadvantages; -if one component faulty, the rest also faulty
-if more components added brightness decreases bc more resistance
-if one component faulty, whole circuit stops
parallel advantages; -if more components added,brigthness not affected
-components can be indovually controlled
-if one faulty rest not affected
disadvantages;-all bulbs have same voltage as supply so can’t be controlled separately
-moe wires

98
Q

what is the total resistance in series circuit

A

total= v1+v2+v3

99
Q

as you add more components in parallel, what happens to the total resistance and explain why

A

total resistance decreases, because more components for current to pass through so overall current increases. current is inversely proportional to resistance when voltage is the same, so therefore total resistance decreases.

100
Q

describe the current and voltage in series and then parallel circuits

A

current in series, same across every component
voltage in series, shared across each component and adds up to total supplied
current in parrallel; shared between each branch but adds up to total supplied
voltage in parallel; same across each branch

physics (10 decks)

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