Electricity Flashcards
1
Q
What is the function of a cell or battery in a circuit?
A
Provides the circuit with a source of potential difference
A battery consists of two or more cells.
2
Q
What is a fixed resistor?
A
Limits the flow of current and has a resistance that cannot change.
3
Q
What is a variable resistor?
A
A resistor with a slider that can change its resistance, often used in dimmer switches and volume controls.
4
Q
How does the resistance of a thermistor change with temperature?
A
Resistance decreases as temperature increases.
5
Q
What is an LDR?
A
A light-dependent resistor whose resistance decreases as light intensity increases.
6
Q
What does a diode do?
A
Allows current to flow in one direction only.
7
Q
What is the purpose of an ammeter?
A
Used to measure the current in a circuit and is connected in series.
8
Q
What is the purpose of a voltmeter?
A
Used to measure potential difference and is connected in parallel with the component.
9
Q
What is the significance of a closed path in a circuit?
A
Electrons need to flow in a complete loop for current to flow.
10
Q
What must be true for a circuit to be connected?
A
The switch must be closed.
11
Q
What is the unit of potential difference?
A
Volts (V).
12
Q
What is electric current?
A
The flow of electrical charge measured in amperes (A).
13
Q
What is the direction of conventional current?
A
From the positive terminal of a cell to the negative terminal.
14
Q
What is resistance?
A
The opposition to current, measured in Ohms (Ω).
15
Q
How does resistance affect current?
A
Higher resistance results in lower current.
16
Q
What are the control variables in an experiment investigating the resistance of a wire?
A
- Potential difference of the power supply
- Temperature of the wire
17
Q
What shape should the graph of resistance against length of wire be?
A
A straight line through the origin with a positive correlation.
18
Q
What happens to resistance as the length of wire increases?
A
Resistance is directly proportional to the length of the wire.
19
Q
What is the method for measuring resistance in a wire?
A
Set up a circuit, measure potential difference and current, and calculate resistance using R = V/I.
20
Q
How does the current behave in a closed-loop circuit?
A
The current is the same at each point in a closed-loop.
21
Q
What is the aim of the experiment?
A
To investigate how combinations of resistors in series and parallel affect the total resistance in electrical circuits.
22
Q
What is the independent variable in the experiment?
A
Number of resistors.
23
Q
What is the dependent variable in the experiment?
A
Total resistance, R.
24
Q
What are the control variables in the experiment?
A
- Potential difference of the power supply
- Temperature of the resistors
25
In a series connection, how is the total resistance calculated?
The resistance of the combined resistors is equal to the sum of the two individual resistances.
26
In a parallel connection, how is the total resistance calculated?
The resistance of the combined resistors is less than the sum of the two individual resistances.
27
What systematic error should be avoided during measurements?
The first crocodile clip must start at 0 on the ruler to avoid zero error in measurements.
28
What is Ohm's Law?
The current through a conductor is directly proportional to the potential difference across it.
29
What is the equation for Ohm's Law?
V = IR.
30
What type of conductors obey Ohm's Law?
Ohmic conductors.
31
What is an example of a non-ohmic conductor?
Filament lamp.
32
How does temperature affect the resistance of a thermistor?
As the temperature increases, the resistance of a thermistor decreases.
33
What does an LDR do?
It changes resistance depending on the light intensity.
34
What is a diode?
A non-ohmic conductor that allows current to flow in one direction only.
35
What is the role of a variable resistor in an experiment?
To vary the voltage across the component.
36
What happens to the resistance in a filament lamp as temperature increases?
The resistance increases as the temperature of the filament increases.
37
What is the I-V graph of an ohmic conductor?
A straight line through the origin.
38
Fill in the blank: The resistance of a _______ changes depending on the light intensity.
[LDR]
39
Fill in the blank: A thermistor is a _______ conductor and a temperature-dependent resistor.
[non-ohmic]
40
What should be done between readings in experiments to prevent heating?
Switch off the circuit.
41
What type of components are linear?
* Fixed resistors
* Wires
* Heating elements
42
What type of components are non-linear?
* Filament lamps
* Diodes & LEDs
* LDRs
* Thermistors
43
What is the effect of increasing temperature on the resistance of a conductor?
An increase in temperature causes an increase in resistance.
44
What is the purpose of a thermistor in a thermostat?
To automatically regulate temperature or activate a device when the temperature reaches a certain point.
45
What safety considerations should be taken when dealing with high currents?
* Never touch the wire directly when the circuit is switched on
* Switch off the power supply if burning is smelled
* Keep liquids away from the equipment
46
What is the expected shape of the I-V graph for a filament lamp?
A curve, indicating it is a non-ohmic conductor.
47
How can you investigate the relationship between the resistance of a thermistor and temperature?
By recording voltmeter and ammeter readings as the temperature changes.
48
What should be included in the circuit diagrams for measuring resistance?
* Ammeter connected in series
* Voltmeter connected in parallel
* Component with appropriate circuit symbol
* Power supply with low voltage (below 15 V)
49
What are the two ways of joining electrical components?
In series and in parallel
50
What is a series circuit?
A string of two or more components connected end to end
51
What is a parallel circuit?
Two or more components attached along separate branches of the circuit
52
In a series circuit, how does current behave?
The current is the same at all points through each component
53
How is the total potential difference shared in a series circuit?
It is shared between the components
54
How do you calculate the total resistance in a series circuit?
The total resistance is the sum of the resistance of each component
55
In a parallel circuit, how is the total current calculated?
The total current is the sum of the currents through the separate components
56
What is the potential difference across each component in a parallel circuit?
The potential difference across each component is the same
57
How does adding resistors in series affect total resistance?
The total resistance increases
58
What happens to total resistance when resistors are connected in parallel?
The total resistance decreases
59
What is the equation for total resistance in series for two resistors R1 and R2?
R = R1 + R2
60
What is a direct current (d.c.)?
A current that is steady and constantly flowing in the same direction
61
What is an alternating current (a.c.)?
A current that continuously changes its direction
62
What is the frequency of mains electricity in the UK?
50 Hz
63
What potential difference does UK mains electricity provide?
Around 230 V
64
What are the three wires in a three-core cable?
* Live wire
* Neutral wire
* Earth wire
65
What color is the live wire in the UK?
Brown
66
What color is the neutral wire in the UK?
Blue
67
What color is the earth wire in the UK?
Green and yellow stripes
68
What is the purpose of the live wire?
Carries the alternating potential difference from the mains supply to a circuit
69
What is the purpose of the neutral wire?
Completes the circuit to the live wire
70
What is the purpose of the earth wire?
Acts as a safety wire to prevent electric shocks
71
What happens if a live wire touches the case of an appliance?
The case becomes electrified, posing a risk of electrocution
72
How does the earth wire enhance safety in electrical appliances?
Provides a low resistance path to the Earth, causing the fuse to melt and cut off the electricity supply
73
What is the voltage of the live wire?
Around 230 V
74
What is the voltage of the neutral wire?
Close to 0 V
75
What is the voltage of the earth wire?
0 V
76
True or False: The earth wire carries electricity during normal operation.
False
77
Fill in the blank: The total resistance in a parallel circuit is ______ than the resistance of the smallest individual resistor.
less
78
What happens when there is a potential difference between live and earth?
A large current can pass through them, providing a potentially lethal shock
## Footnote
This is a fundamental concept in electrical safety.
79
What do electricians do before working with electrical appliances?
Switch off the mains electricity supply to the whole house or section of a house
## Footnote
This is crucial to avoid contact with live wires.
80
Why do electricians need to switch off the mains electricity?
They will come into contact with live wires when they are working
## Footnote
This reduces the risk of electric shock.
81
What is the potential difference of the live wire?
230 V
## Footnote
This is the standard voltage for mains electricity in many regions.
82
What is the potential of the electrician when working on live wires?
0 V
## Footnote
This is considered the reference potential for safety.
83
What occurs due to the potential difference between the live wire and the electrician?
A current would pass through the electrician's body to reach the earth
## Footnote
This is the principle behind electric shock.
84
True or False: A device can cause an electric shock even if it is switched off.
True
## Footnote
If the mains supply is on, the live wire can still pose a risk.
85
Fill in the blank: The potential difference between the live wire and the electrician is large enough to cause a _______.
current to pass through
## Footnote
This is a critical safety concern in electrical work.
86
What is power defined as?
The rate of energy transfer or the amount of energy transferred per second.
87
What factors does the power of a device depend on?
* Voltage of the device
* Current of the device
88
What is the unit of power?
Watt (W), which is the same as a joule per second (J/s).
89
How is power calculated in terms of voltage and current?
P = VI
90
What is the formula for calculating power in terms of resistance?
P = I²R
91
True or False: The voltage across an electric device is independent of current and resistance.
False
92
What is the relationship between power and energy in appliances?
The amount of energy transferred depends on the time the appliance is switched on and the power of the appliance.
93
Fill in the blank: A 1 kW iron uses the same amount of energy in 1 hour as a _______ iron would use in 30 minutes.
2 kW
94
What does work done equal when charge flows through a circuit?
Energy transferred.
95
What is the formula for calculating energy transferred?
E = Pt
96
What does the equation E = IVt represent?
Energy transferred in terms of current, potential difference, and time.
97
What is the power rating of an appliance?
The amount of energy it transfers by electrical working every second.
98
What information is typically found on the label of a domestic electrical appliance?
* Potential difference required
* Frequency of the supply
* Power rating in Watts
99
What does the National Grid do?
Distributes electricity across the UK.
100
What are the two types of transformers used in the National Grid?
* Step-up transformers
* Step-down transformers
101
How does a step-up transformer increase efficiency?
It increases voltage and decreases current, reducing heating due to resistance.
102
How does a step-down transformer function?
It decreases the potential difference for domestic use.
103
What type of current is produced in power stations?
Alternating current (AC).
104
True or False: Transformers are used only to increase potential difference.
False
105
What is the equation that relates power, current, and voltage?
P = IV
106
Fill in the blank: The current generated by power stations is greater than that which is required for _______.
homes and other buildings
107
What is the significance of using high potential difference in power transmission?
It reduces the current and therefore less energy is dissipated as heat.
108
How does energy transfer occur in a circuit?
As charge flows, energy is transferred from the power source to the components.
109
What is the energy transferred when charge flows through a resistor?
It makes the resistor hot.
110
What is a mnemonic to remember the relationship between power, current, and resistance?
"Twinkle Twinkle Little Star, Power equals I squared R!"
111
What happens if an appliance is plugged into a mains supply with a much higher voltage than stated on its label?
It could fuse or set on fire and become damaged.
112
What are the three types of charge a particle can have?
Positive, Negative, Neutral
## Footnote
Electrons are negatively charged, protons are positive, and neutrons are neutral.
113
What happens to the overall charge of an atom when the number of electrons equals the number of protons?
The overall charge of the atom is zero.
114
How does an object become negatively charged?
An object becomes negatively charged when it gains electrons.
115
How does an object become positively charged?
An object becomes positively charged when it loses electrons.
116
What are the two types of forces that charged objects can exert on each other?
Attractive and Repulsive.
117
True or False: Opposite charges repel each other.
False.
118
What is charging by friction?
Charging by friction occurs when certain insulating materials are rubbed against each other, causing them to become electrically charged.
119
What is the result when an acetate rod is rubbed with a cloth?
The acetate rod becomes positively charged and the cloth becomes negatively charged.
120
What is static electricity?
Static electricity is caused by a build-up of stationary charge on a surface.
121
Give two examples of static electricity.
* Hair sticking up after combing * Rubbing a balloon and sticking it to a wall.
122
What causes sparking?
Sparking occurs when there is a large potential difference between two objects.
123
What is an earthed conductor?
An earthed conductor is a wire that allows a current to flow to the Earth.
124
What can cause a large spark in the air?
The breakdown of air due to a strong electric field.
125
How does lightning occur?
Lightning occurs from the build-up of charge in clouds, where ice crystals rub against each other, creating a potential difference.
126
What is the purpose of a bonding line when refuelling an airplane?
To connect the fuel tank to the Earth, allowing excess charge to dissipate.
127
What creates an electric field around a charged object?
A charged object creates an electric field around itself.
128
In which direction do electric field lines point?
Away from positive charges and towards negative charges.
129
What is the relationship between the strength of an electric field and distance from the charged object?
The field is strongest close to the charged object and becomes weaker further away.
130
What happens to objects in an electric field with the same charge?
They experience a repulsive force.
131
What happens to objects in an electric field with opposite charges?
They experience an attractive force.
132
What can happen if an electric field becomes strong enough?
It can force charges through insulators, creating a spark.
133
What is a uniform electric field?
A uniform electric field is represented by straight parallel lines from positive to negative.
134
What must be included when drawing electric field lines?
The direction with arrows pointing in the correct direction.
