P2- Electricity Flashcards

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1
Q

Define current

A

The flow of charged particles

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2
Q

The _ the resistance across a component, the _ the current that flows

A

Greater

Smaller

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3
Q

What is the equation for total charge

A

Charge flow = Current X time

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4
Q

What is the equation for potential difference

A

Potential difference=Current X resistance

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5
Q

What do ohmic conductors have

A

Constant resistance

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6
Q

What does LDR stand for

A

Light dependent resistor

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7
Q

What does the resistance of a thermistor depend on

A

Temperature

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8
Q

What happens to the resistance of a thermistor in different temperatures

A

Hot goes up cold goes down

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9
Q

How can you use LDRs and thermistors

A

in sensing circuits

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10
Q

How can sensing circuits be used

A

To turn on or increase the components depending on the conditions they are in

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11
Q

How are components arranged in a series circuit

A

Around in a line

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12
Q

What is the equation for total potential difference in a series circuit

A

Vtotal=V1+V2+…

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13
Q

What is the equation for current in a series circuit

A

I1=I2…..

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14
Q

What is the equation for total resistance in a series circuit

A

Rtotal=R1+R2

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15
Q

What is the equation for potential difference in a parallel circuit

A

V1=V2

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16
Q

What is the equation for current in a parallel circuit

A

Itotal=I1+I2+…

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17
Q

What does adding a resistor do to the total resistance in a parallel circuit

A

Reduces the total resistance

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18
Q

What type of supply is the mains supply

A

AC

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19
Q

What type of battery supply is used

A

DC

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20
Q

What does AC current do

A

Constantly change direction

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21
Q

What does DC current do

A

Constantly flow in the same direction

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22
Q

How many wires do most cables have

A

3

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23
Q

What are the 3 different wires in most cables

A
  • Live wire
  • Neutral wire
  • Earth wire
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24
Q

What is the live wire

A

The wire provides the alternating potential difference from the main supply

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25
Q

What is the neutral wire

A

The neutral wire completes the circuit- when the appliance is operating normally, current flows through the live and neutral wires

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26
Q

What is the Earth wire

A

It’s protecting the wiring, and for safety - it stops the appliance casing from becoming live. It doesn’t usually carry a current- only when there is a fault

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27
Q

Can the live wire give you an electric shock

A

Yes

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28
Q

What is the equation for energy transferred

A

Energy transferred= Power(w) X Time(s)

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29
Q

What is the equation for energy transferred

A

E= Charge flow X potential difference

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30
Q

What is the equation for power including potential difference and current

A

P =VI

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31
Q

What is the equation for power including resistance and current ( this may be wrong)

A

P=I^2R

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32
Q

What is potential difference changed by

A

A Transformer

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33
Q

What does a build up of static electricity cause

A

Friction

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34
Q

When too much static electricity causes a spark what is there a lot of

A

Potential difference

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35
Q

Similar charges _ ,opposite charges _

A

Repel

Attract

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36
Q

What do electric charges create

A

Electric field

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37
Q

Where is an electric field created around

A

Electrically charged object

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38
Q

How can you show an electric field

A

Field lines

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39
Q

Charged objects in an electric field fell a _

A

Force

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40
Q

When are sparks caused

A

When there is a high enough potential difference between a charged object and the Earth

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41
Q

Define charge

A

Value of electricity flowing in a circut

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42
Q

Define current

A

Flow of electrons

43
Q

Define potential difference

A

Pushes current around

44
Q

Define define resistance

A

Anything that slows down the current

45
Q

Give two example of when a thermistor may be used

A
  1. In a thermistat to turn a heater on below a certain tempreture
  2. In a freezer to turn on a cooler when the temperature becomes too high
46
Q

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

A

The LDR’s resistance increases

47
Q

Give an application for an LDR

A

○ Street lights

○ When light levals become too low, the light gains sufficient current to turn on

48
Q

State the equation linking charge, current
and time. Give the units for the quantities
involved.

A

Q = I t
Charge (Coulombs), Current (Amperes),
Time (Seconds)

49
Q

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

A

Current is the same at all points in a

closed loop

50
Q

What two factors does the current in a

circuit depend on?

A
  1. Potential Difference (V)

2. Resistance (R)

51
Q

What equation should be used to
calculate potential difference if current
and resistance are known? State the
units for all 3 quantities.

A
V = I R
Potential Difference (V), Current (A),
Resistance (Ω)
52
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
53
Q

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

A
  1. Lamps
  2. Diodes
  3. Thermistors
  4. Light Dependant Resistors (LDRs)
54
Q

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

A

● Resistance increases
● Ions in metal have more energy, so vibrate
more, causing more collisions with
electrons as they flow through the metal,
creating greater resistance to current flow

55
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

56
Q

State what happens to the resistance of

a thermistor as temperature increases.

A

The thermistor’s resistance decreases.

57
Q

Give two examples of when a thermistor

may be used.

A
  1. In a thermostat to turn a heater on
    below a certain temperature
  2. In a freezer to turn on a cooler when
    the temperature becomes too high
58
Q

State what happens to the resistance of

a LDR as light intensity decreases.

A

The LDR’s resistance increases.

59
Q

Give an application for a LDR.

A

● Street lights often use LDRs
● When light levels become too low, the
light gains sufficient current to turn on

60
Q

What are the two ways that a component

can be connected in a circuit?

A
  1. Series (same loop)

2. Parallel (adjacent loop)

61
Q

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

A

● Series: Total P.D is shared between
each component
● Parallel: P.D across each component
is the same

62
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.

63
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

64
Q

Describe the current in a series circuit.

A

In a series circuit, the current is the same
at all positions since the charge only has
one path to flow through.

65
Q

Describe the current in a parallel circuit.

A

In a parallel circuit, the current is shared
between the different branches. When
the charge reaches a junction it splits.

66
Q

How should you connect an ammeter in a circuit to

measure current?

A

Ammeters should be connected in series
with the component that they are
measuring current through.

67
Q

How should you connect a voltmeter in a

circuit to measure potential difference?

A

Voltmeters should be connected in
parallel to the component that they are
measuring the potential difference of

68
Q

Why is it advantageous to connect lamps in parallel?

A

If one lamp blows, the rest will be
unaffected and can still receive current
(i.e. the circuit is still complete).

69
Q

Is mains electricity an a.c supply or a d.c
supply? What do each of these stand
for?

A

Mains electricity is an a.c supply

a. c. : Alternating Current
d. c. : Direct Current

70
Q

Define alternating current and direct current.

A
● Alternating current: Current that
continuously changes direction at a
specific frequency
● Direct current: One directional current
flow
71
Q

What is the frequency and voltage of the UK mains

electricity supply?

A

● Frequency: 50 Hz

● Voltage: 230V

72
Q

How many wires are usually in the cables connecting
electrical appliances to the mains? Name these
wires.

A
  1. Live wire
  2. Neutral wire
  3. Earth wire
73
Q

State the insulation colour used on the Earth wire.

A

Green and Yellow Stripes

74
Q

State the insulation colour used on the live wire

A

Brown

75
Q

State the insulation colour used on the Earth wire.

A

Blue

76
Q

Explain when the Earth wire does and doesn’t carry

a current.

A

● Under normal circumstances, no current
flows through the Earth wire
● If a fault occurs in the appliance (such as a
surge or the casing becoming live), current
will flow to the ground

77
Q

What potential is the neutral wire at?

A

0 Volts

78
Q

State the potential difference between the live and

earth wires.

A

230 Volts

79
Q

What is the purpose of the neutral wire?

A

To complete the circuit by connecting the

appliance back to the mains supply.

80
Q

For metal appliances, where is the Earth wire

connected to? Why?

A

● Earth wire is connected to the metal casing
of the appliance
● If live wire becomes loose and touches the
casing, the current will flow through the
Earth wire, preventing electrocution

81
Q

State two equations for the power of a circuit. Give

appropriate units.

A

P = I V P = I² R
Power (Watts), Current (Amperes)
Potential Difference (Volts), Resistance
(Ohms)

82
Q

State an equation linking energy transferred, power

and time. Give appropriate units.

A

E = P t
Energy (Joules), Power (Watts), Time
(Seconds)

83
Q

State an equation linking energy transferred, power

and time. Give appropriate units.

A
E= Q V
Energy (Joules), Charge (Coulombs),
Potential Difference (Volts)
84
Q

What two main factors does the amount of energy

transferred by an appliance depend on?

A
  1. How long the appliance is being used
    for
  2. The power of the appliance
85
Q

Describe the energy transfers in a battery powered

torch.

A
● Battery converts chemical energy into
electrical energy
● Bulb converts electrical energy into light
as well as waste energy in the form of
heating
86
Q

Describe the energy transfers in a battery powered

motor.

A
● Battery converts chemical energy into
electrical energy
● Motor converts electrical energy into
kinetic energy as well as waste energy
in the form of heating due to friction
87
Q

What three things determine the power of a circuit

device?

A
1. The potential difference across the
circuit
2. The current through the circuit
3. The amount of energy transferred in a
given time
88
Q

What is the purpose of the National Grid?

A

To link power stations to consumers so
that they have access to a source of
electricity.

89
Q

What are the two types of transformers used in the

National Grid?

A
  1. Step-Up Transformers

2. Step-Down Transformers

90
Q

Where are step-up transformers found in the

National Grid? What do they do?

A

● Step-Up Transformers are used when
connecting power stations to
transmission cables
● They increase the potential difference

91
Q

Where are step-down transformers found in the

National Grid? What do they do?

A

● Step-Down Transformers are used in
connecting transmission cables to
domestic buildings (like houses)
● They decrease the potential difference

92
Q

Why do transmission lines transfer electricity at high

potentials?

A

● A high potential, results in a low current
● The lower the current, the less energy
that is wasted as heat
● Therefore it is more efficient

93
Q

Why does the potential need to be decreased

between transmission lines and houses?

A

● Lower potentials are safer for domestic
use and reduces the likelihood of
severe electrocution
● Appliances are designed for 230V

94
Q

What can happen when insulating

materials are rubbed together?

A

They can become (statically) electrically

charged.

95
Q

Why can insulators become electrically charged

when rubbed together?

A

● Electrons are rubbed from one material onto the
other
● The material gaining electrons becomes
negatively charged
● The material losing electrons becomes equally
positively charged

96
Q

What happens when two electrically charged objects

are brought close together?

A

They exert a force on each other

97
Q

What happens when two identically charged objects

are brought close together?

A

They exert a repulsive force on each

other and repel.

98
Q

What happens when two oppositely charged objects

are brought close together?

A

They exert an attractive force on each

other and attract.

99
Q

Give an example of a non-contact force.

A

The repulsive or attractive force acting

between two electrically charged objects.

100
Q

What is an electric field?

A

A region in which a charged object will

experience a non-contact electrical force.

101
Q

Where can electric fields be found?

A

Surrounding any charged object.

102
Q

Describe the electric field around a

charged particle.

A

● Strongest closest to the object
● Decreases in strength as you move
away from the object

103
Q

What happens to the force between two charged

objects when they are moved closer together?

A

The force between them becomes

stronger as the separation reduces.

104
Q

In situations where sparks are unwanted,
what precaution must be taken to
prevent the build up of static charge?

A

Any surfaces that are rubbing against
each other should be earthed to allow
the charge to flow off the materials.