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P2 – Electricity
Pupil Booklet - Foundation
Electricity
Name…………………………….
Teacher.....................................
Lab……………………………….
1
P2 – Electricity
Pupil Booklet - Foundation
Exam Information
Date of examination ……………………………………………………..
Percentage of GCSE ……………………………………………………
Style of examination ……………………………………………………..
Length of examination …………………………………………………..
UMS conversion chart
A*
45
90
A
40
80
B
35
70
C
30
60
D
25
50
E
20
40
F
15
30
G
10
20
My target grade is…………………….
400
380
360
340
320
300
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
Record of achievement
A*
A
GCSE exams
Module
UMS
B
PHY1A
C
D
PHY1B
E
PHY2
F
G
PHY3
Learning conversations
Date
To improve I must…………..
2
Grade
ISA
Assessment
Mark
Grade
P2 – Electricity
Pupil Booklet - Foundation
Electricity
Assess your knowledge and understanding at different times during this section of the module. Use
the following key
Describe how insulating materials can become charged using key terms charge and
friction
Use the golden rules for static electricity to explain how static electricity is used in
different situations
Describe how a photocopier works
Explain how the build up of charge can be dangerous in different situations
Describe how the build up of charge can be controlled or prevented
Explain how earthing using a conductor can discharge a charged object
Describe how the build up of charge can lead to a spark using key terms potential
difference, charge and electrons
Define electric current
Describe how current can be controlled in a circuit using the terms resistance and
potential difference
Use the equation energy transferred = potential difference x charge
State the units of potential difference, current, power, charge, energy , resistance and
frequency
Use the equation charge = current x time in seconds
Recognise the voltage-current graphs for a fixed resistor, filament bulb and diode
Use the equation potential difference = current x resistance
Interpret the gradient of a voltage-current graph in terms of resistance
Calculate resistance from a voltage-current graph
Recognise series and parallel circuits
State the rules for series and parallel circuits
Use the rules for series circuits to calculate potential difference, current and resistance
Use the rules for parallel circuits to calculate potential difference and current
Recognise all the common circuit symbols including those for the diode, thermistor, light
dependent resistor and fuse
Draw a voltmeter on a circuit to measure potential difference (in parallel)
Draw an ammeter on a circuit to measure current (in series)
Read off values of resistance from a graph of light intensity against resistance for a light
dependent resistor
Read off values of resistance from a graph of temperature against resistance for a
thermistor
Name and label the different parts of a 3-pin plug
State the function of the fuse and cable grip
Recognise mistakes in the wiring of a 3-pin plug
3
End
Outcome: I should be able to
Middle
no knowledge or understanding
some knowledge or understanding – needs more work
confident in knowledge or understanding
Start
Red:
Yellow:
Green:
P2 – Electricity
Pupil Booklet - Foundation
Recognise dangerous situations involving mains electricity
Use the equation power = current x voltage
Use the equation power = current x voltage to calculate normal working current of an
electrical device
State which fuse to install in an appliance based on normal working current
State the danger of installing a fuse of too high a rating
Explain how an earth wire protects the user from getting an electric shock if a fault
occurs
Explain why some devices don’t require an earth wire
State UK mains frequency and voltage
Mark the time period for one cycle on an oscilloscope trace
Calculate frequency using frequency = 1/time period
State the units of frequency
Describe the difference between alternating and direct current
Describe how the potential of the live and neutral terminals vary with respect to each
other
Calculate peak voltage from an oscilloscope trace
Convert values using prefixes such as kilo(k), mega (M), and milli(m). Other prefixes may
be used in questions but the examiner will tell you what the prefix means in standard
form on the paper
NOTE: Equation in bold will not be given, learn it! Frequency = 1/time period for one cycle
How Science works
Identify independent and dependent variables
State whether a variable is discrete, continuous, categoric or ordered
Identify control variables
Describe how to improve the reliability of results
State the range of a set of measurements
State the interval between measurements
Identify anomalous results and describe how to deal with them
Calculate the mean of a set of results
Assess the precision of a measuring device
Explain how to improve the precision of results
Identify directly proportional relationships
Identify directly proportional squared relationships
Select the correct way to represent results depending on the type of variables used in the
experiment – bar chart or line graph
Plot points on a graph
Draw a line or curve of best fit
Explain how to deal with zero errors
4
End
Outcome: I should be able to
Middle
Start
These HSW aspects are covered in this booklet. You will need to know more than just these for ISAs.
P2 – Electricity
Pupil Booklet - Foundation
Static Electricity
In this lesson, you will learn golden rules for static electricity and how
objects become charged. You will then use the golden rules to help explain
different phenomena with static electricity.
Atomic Structure
Understanding static electricity starts with atomic structure.
1. Label the diagram of the atom below.
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.
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2. Complete this table to show the charge and relative mass of each particle within an atom.
Particle
Charge
Relative mass
Proton
Neutron
Electron
3. Write your golden rules for static electricity here. Learn these rules and you will be able to apply
this knowledge in questions in the exam.
GOLDEN RULES
1. ……………………………………………………………………………………………………
2. ……………………………………………………………………………………………………
3. ……………………………………………………………………………………………………
4. ……………………………………………………………………………………………………
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P2 – Electricity
Pupil Booklet - Foundation
How objects become charged
4. When a glass rod is rubbed with a cloth, the glass rod becomes negatively charged.
a) Explain how the rod becomes negatively charged. Draw a diagram to help your description.
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b) What charge is left on the cloth? Explain your answer.
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5. Another rod is rubbed with a different cloth. This time the glass rod becomes positively charged.
a) Explain how the rod becomes positively charged. Draw a diagram to help your description.
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b) What charge is left on the cloth? Explain your answer.
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6. When a computer screen is polished with a cloth, it soon becomes covered in dust again.
a) Explain why the dust is attracted towards the computer screen.
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b) Does it matter if the screen becomes positively or negatively charged? Explain your answer.
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P2 – Electricity
Pupil Booklet - Foundation
7. If you put your hands on the dome of a Van der Graaff generator your hair stands on end. Explain
why.
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8. When you rub a balloon against your hair, your hair sticks to the balloon. Explain why. Assume
that the balloon becomes negatively charged.
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9. An insecticide spray gun forces insecticide out through a very fine nozzle. The insecticide
droplets become positively charged.
a) Explain how the droplets become charged.
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b) What charge will be on the nozzle of the spray gun and why?
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P2 – Electricity
Pupil Booklet - Foundation
Uses of static electricity
How to remove the dirt from smoke
Smoke from industrial chimneys such as those at coal fired power stations contains tiny bits of dirt.
This dirt falls on houses and gardens. If people breathe in the dirt, it can damage their lungs.
The diagram shows how the dirt can be removed from factory chimneys using a smoke precipitator.
Explain how the precipitator works.
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How to make a spray hit its target
Bicycle frames can be painted using an electrostatic paint spray. Each paint droplet leaves the spray
gun with a positive charge. The bicycle frame is given a negative charge.
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P2 – Electricity
Pupil Booklet - Foundation
Explain why the paint droplets are all given a positive charge
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Explain why the bicycle frame is given a negative charge
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How a photocopier works
There is little value in learning how a
photocopier works but the exam board still
insists on leaving it on the specification for
the course. There is no real application of
knowledge just a regurgitation of a certain
sequence. Learn the sequence of events in
case it comes up in the exam!
9
P2 – Electricity
Pupil Booklet - Foundation
Danger from sparks
The most obvious danger of an electrostatic spark is lightning but there
are many situations where the build up of charge needs to be either
prevented or controlled. You will learn about the measures taken and
the theory behind how they work.
Refueling petrol tankers and planes
1. What causes the build up of charge on a petrol tanker?
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2. What causes the build up of charge on a plane?
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3. When fuel is pumped either out of the tanker or into the
plane there are fumes that are highly flammable. What could
happen if there was a build up of charge on the bodywork?
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4. Describe and explain how the petrol tanker or plane is made safe before refueling takes place.
Highlight the key words in your answer
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P2 – Electricity
Pupil Booklet - Foundation
Preventing explosions at flour mills
I doubt you’ve ever walked into the kitchen, seen a bag of flour and been
afraid. However, flour can be very dangerous because it contains a lot of
energy. Flour contains complex carbohydrates that are the basis for the
energy supplying part of our diets.
1. How does charge build up on the pipe feeding the metal vat?
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2. Why could this be dangerous?
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3. Look at the diagram below. Describe and explain how charge is prevented from building up on
the pipe and vat.
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Why does Earthing work?
Look at the diagrams and complete the following sentences.
When a negatively charged, conducting
object is earthed, ______________ move
from the object to the earth.
When a positively charged object is earthed,
electrons move from the __________ to the
__________.
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P2 – Electricity
Pupil Booklet - Foundation
Making hospital operating theatres safe
In a hospital operating theatre, there are several potential dangers
A. The drug used to make the patient unconscious is explosive
B. There are open wounds
C. The air may be treated so that it has a higher than usual
oxygen content
1. Explain how the build up of charge could cause each of the potential dangers listed above to
become a major problem.
A.……………………………………………………………………………………………………………
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B.……………………………………………………………………………………………………………
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C.……………………………………………………………………………………………………………
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2. The operating theatre and the clothes used by hospital staff and patients are designed to reduce
risks. Explain each of the following designs for the theatre or clothing by referring to the potential
dangers listed above.
a) the patient and staff where low friction clothing
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b) the patient has a conducting wire attached to their clothing that is then earthed
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c) the floor is made from a conducting material
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P2 – Electricity
Pupil Booklet - Foundation
From static to current electricity
The amount of charge that has flowed in a circuit can be calculated using the equation
Charge
=
(in coulombs)
Current
(in amps)
x
time
(in seconds)
1. Draw the equipment used to demonstrate changing static electricity to current electricity.
2. What is an electric current? Use key words in your answer.
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3. A current of 1.5A flows through an electric toothbrush for 90 seconds. How much charge has
flowed through the toothbrush?
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4. 350 coulombs of charge flows through an iron in 70 seconds. What is the current flowing through
the iron?
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5. If a current of 2A flows through a bulb for 5 minutes, how much charge has passed through the
bulb?
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P2 – Electricity
Pupil Booklet - Foundation
6. How long would it take for 2000 coulombs of charge to flow through a motor if the current is 2.5A?
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7. A wind up radio uses two rechargeable cells, each capable of storing 1800 coulombs of charge.
a) For how long can the radio be used without recharging the cells if the radio uses 0.5A of
current?
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b) If the owner recharges the cells for 5 minutes, how much charge will be stored in the cells if
the total current flowing to the cells is 1.5A?
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8. Roberta and Eugene were trying to work out how much charge there was stored in different
electric toothbrush batteries. They measured the current flowing into toothbrush when it was
switched on and timed how long it took to run the batteries down. The toothbrush required two
batteries. They repeated their experiment twice. Here are their results.
Battery
Current flowing
Time taken (seconds)
(Amps)
1
2
3
Longalast
1.15
965
944
957
Durablast
1.25
888
900
768
Morelife
1.20
915
900
909
Charge flowed
Mean
(Coulombs)
a) Circle the anomalous result in the table.
b) Calculate the mean average for each brand of battery.
c) Calculate the amount of charge stored by each brand of battery.
d) How would you present the results of this experiment? Justify your answer.
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14
P2 – Electricity
Pupil Booklet - Foundation
Modeling Electrical Circuits 1 - Current
Modeling electrical circuits can help us to understand
the jobs of different components in a circuit and the
meanings of terms like current, potential, potential
difference, charge and resistance. It is vital that you
understand these terms if you are going to
understand electrical circuits.
1. In the coal truck model of electrical circuits (above), coal is taken from the coal mine to the
power station in trucks on railway lines. Each part of the model represents a part of an
electrical circuit. Which part of an electrical circuit is represented by:
a) The coal mine?
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b) The power station? …………………………………………………………………………......
c) The trucks?
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d) The coal?
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e) The tracks?
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2. How could you represent more current flowing using the power station model?
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3. What would happen at the power station if more current were to flow?
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4. How is this similar to an electrical circuit?
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5. Does the model show current getting used up or not? Explain your answer.
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15
P2 – Electricity
Pupil Booklet - Foundation
Modeling Electrical Circuits 2 – Potential Difference
The term potential difference sounds new but has a similar meaning to
a word you have used before, voltage. In this lesson you will learn
what the terms potential, voltage and potential difference mean.
And by the way, no eating the Smarties!
1. Draw a diagram of the circuit model you have used. State and explain what each part of the
model represents. Indicate where energy is transferred to and from the electrons.
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2. Use the model to explain what the term potential difference means and how it is slightly different
from voltage or potential.
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3. This model shows how the law of conservation of energy is obeyed in electrical circuits. Explain
how the law of conservation of energy is obeyed using this model.
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16
P2 – Electricity
Pupil Booklet - Foundation
Why do sparks fly?
1. Explain why a spark flies from the dome to the
ball using the key words charge, potential
difference and electrons.
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The energy transferred by the charge is measured in joules and can be calculated using the
equation:
Energy transferred
(in joules)
=
potential difference
x
(in volts)
charge
(in coulombs)
3. How much energy is transferred by 3000 coulombs of charge flowing through a bulb with a
potential difference of 12V across it?
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4. What is the potential difference across a motor if 100 coulombs of charge transfer 450J of
energy?
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5. How much charge needs to flow through a hairdryer to transfer 6.9MJ of energy if the potential
difference across the bulb is 230V?
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P2 – Electricity
Pupil Booklet - Foundation
6. Lightning is caused by the build up of charge within a thunder cloud.
a) Explain why a lightning bolt occurs. Use key words in your
answer.
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b) There is a potential difference of 6MV between the cloud and the ground. If a lightning bolt
strikes and transfers 12KJ of energy, how much charge has flowed during the strike?
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Controlling Current in Circuits
Draw the circuit diagram for the circuit you set up. Explain how you controlled the current in the
circuit.
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Resistance, potential difference and current are linked by this equation:
Potential difference
(in volts)
=
current
(in amps)
x
resistance
(in ohms,Ω)
18
P2 – Electricity
Pupil Booklet - Foundation
Circuit Symbols
Match the symbol to the component and its function.
Symbol
Component
Function
ammeter
Measures potential difference
battery
Resists the flow of current
cell
Lights when a current flows through
it
voltmeter
Measures the current flowing
filament lamp
Provides energy to the circuit
light dependent
resistor
Provides energy to the circuit
resistor
Varies the resistance of a circuit
variable resistor
Breaks the circuit if too much current
flows
fuse
Its resistance changes with
temperature
diode
Only allows current to flow through it
one direction
Its resistance changes with light
intensity
thermistor
19
P2 – Electricity
Pupil Booklet - Foundation
How does the length of wire affect the resistance of the wire?
In this investigation, you are going to increase the length of wire in a circuit and see how it affects
the resistance of the wire.
1. The independent variable is ……………………………………………………………………………….
2. This variable is categoric/continuous/discrete/ordered
3. The independent variable is ……………………………………………………………………………….
4. This variable is categoric/continuous/discrete/ordered.
5. State two control variables
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Results
Length of wire
Potential difference across
Current flowing through wire
Resistance
(cm)
the wire (volts)
(amps)
(Ω)
0.0
1
2
Mean
1
2
Mean
0.00
0.00
0.00
0.00
0.00
0.00
0.00
20.0
40.0
60.0
80.0
100.0
6. Circle any anomalies and calculate the mean results and resistances.
7. What is the relationship between the length of wire and the resistance of the wire?
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8. What range of lengths of wire did you use? Include the unit…………………………………………
9. What interval did you use for the lengths of wire? ……………………………………………………..
10. To what precision did you measure the length of wire? ……………………………………………….
11. Draw a line graph of your results. Stick your graph on the next page.
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P2 – Electricity
Pupil Booklet - Foundation
12. Use your graph to estimate the resistance of the wire when its length is 55cm ……………………
13. How much current would flow through a 55cm length of wire when a potential difference of 5V is
across the wire?
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14. Read the following passage and then explain why the resistance of the wire increases as the
length increases.
‘As free electrons flow through a wire they collide with ions in the metal lattice. This causes the
free electrons to transfer some energy to the wire as heat and the free electrons slow down.
These collisions are what cause resistance in a wire.’
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21
P2 – Electricity
Pupil Booklet - Foundation
Voltage-current graph for a fixed resistor
1. Draw the circuit diagram for this experiment
Potential Difference
(V)
1
2
Mean
Current (A)
1
2
Resistance
(Ω)
Mean
2. What can you say about the resistance as the potential difference across the resistor increases?
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3. Write a conclusion about the relationship between potential difference and current.
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4. You should draw a line graph of these results? Why?
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5. Plot a line graph of your results. Plot potential difference along the x axis and current along the yaxis.
6. Why is the potential difference plotted on the x-axis?
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7. Circle any anomalies on your graph.
8. To what precision was the potential difference measured? ……………………………………………
9. To what precision was the current measured? …………………………………………………………
10. What range of potential differences did you use? ………………………………………………………
22
P2 – Electricity
Pupil Booklet - Foundation
11. Stick your graph here.
12. Calculate the gradient of your line. Remember gradient = change in y axis ÷ change in x-axis.
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13. What does the gradient of the line represent? Look at what you have plotted on the axes and
how you calculated the gradient to help you.
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14. Draw the line you would expect to see for a resistor of twice the resistance of your resistor.
Label the line ‘twice the resistance’
15. Draw the line you would expect to see for a resistor of half the resistance of your resistor. Label
the line ‘half the resistance’
23
P2 – Electricity
Pupil Booklet - Foundation
Voltage-current graph for a filament lamp
1. Draw the circuit diagram for this experiment
Potential Difference
(V)
1
2
Mean
Current (A)
1
2
Resistance
(Ω)
Mean
2. What can you say about the resistance as the potential difference across the filament increases?
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3. Why do you think this has happened? Look at your conclusion to the last experiment
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4. Write a conclusion about the relationship between voltage and current.
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5. Should your draw a bar chart or line graph of these results? Justify your answer.
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6. Draw your bar chart or line graph.
7. Circle any anomalies in your table or on your graph.
8. If the ammeter you used had a zero error of 0.02A, what would you do to eliminate this error?
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24
P2 – Electricity
Pupil Booklet - Foundation
Stick your bar chart/line graph here.
Diodes
Diodes are used in many different circuits depending on the need.
For example, light emitting diodes (LEDs) are used to indicate that
something is working. Other diodes are used to protect your
computers and to change alternating current to direct current.
1. In which of these circuits would the filament lamp be on? …………………………………………
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2. Draw the circuit diagram for this demonstration
Potential
Difference (V)
Current (A)
Resistance (Ω)
3. Sketch the voltage-current graph for a diode. Label important points on the graph.
Summary
Sketch the four quadrant graphs for a fixed resistor and a filament lamp on the axes below.
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Series and parallel circuits
In the examination, the first thing that you will need to do to be able to answer a question on circuits
is to identify whether the circuit is series or parallel. You will then need to apply the rules for each
type of circuit and you can then answer any question.
1. What is special about a series circuit?
……………………………………………………………………………………………………………
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2. What is special about a parallel circuit?
……………………………………………………………………………………………………………
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Series Circuits
3. Draw the circuit diagram and tables on the board.
4. What conclusion can you come to about the current flowing in a series circuit?
……………………………………………………………………………………………………………
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5. What is the relationship between the supply potential difference and the potential differences
across the bulbs?
……………………………………………………………………………………………………………
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6. Calculate the resistance of each bulb.
……………………………………………………………………………………………………………
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7. State the total resistance of the circuit ……………………………………………………………....
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Series Circuit Calculations
1.
Each cell in this circuit provides 3V.
a) What is the total potential difference provided by
the cells?
…………………………………………………………
b) Bulb A has a resistance of 2 ohms. Calculate the
potential difference across bulb A.
…………………………………………………………
…………………………………………………………
c) What is the potential difference across bulb B? …………………………………………………………
d) Calculate the resistance of bulb B
…………………………………………………………………………………………………………………
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e) Why do you think there is twice the potential difference across bulb A compared to bulb B?
…………………………………………………………………………………………………………………
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2.
The cells in this circuit are identical.
a)
How much potential difference is provided by the
each cell?
…………………………………………………………
b)
Calculate the total resistance of the bulbs.
…………………………………………………………
…………………………………………………………
c) The bulbs are identical.
i) What is the resistance of each bulb?
……………………………………………………………………………………………………………..
ii) What potential difference would you expect to see across each bulb?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
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Parallel Circuits
1. Draw the circuit diagram and tables on the board.
2. What conclusion can you come to about the potential difference across each branch of a
parallel circuit?
……………………………………………………………………………………………………………
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3. What is the relationship between the current flowing in each branch of a parallel circuit and the
total current flowing in the circuit?
……………………………………………………………………………………………………………
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4. Which bulb in you experiment do you think had the highest resistance? Explain your
reasoning.
……………………………………………………………………………………………………………
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Summary
Golden rules
Series circuits
Parallel circuits
1
1
2
2
3
3
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Parallel Circuit Calculations
1.
The two resistors in this circuit have different
resistances.
a)
How much current flows through resistor B?
………………………………………………………
b) Calculate the resistance of resistor A.
…………………………………………………………
…………………………………………………………
c) Calculate the resistance of resistor B.
………………………………………………………………………………………………………………
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d) Why do you think twice as much current flows through resistor A compared to resistor B?
………………………………………………………………………………………………………………
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2.
Bulbs A, B and C are identical.
a)
How much current will flow through bulb A?
…………………………………………………………
b)
Calculate the resistance of bulb A.
…………………………………………………………
…………………………………………………………
c) How much potential difference will be across bulb B? ………………………………………………...
d) Calculate the resistance of bulb C.
………………………………………………………………………………………………………………..
Extension
e) What is the total resistance of this circuit? Tricky question!
………………………………………………………………………………………………………………
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……………………………………………………………………………………………………………….
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Sensing the environment
The output of an electrical device can be changed by changing the
resistance in the circuit. The resistance can be changed manually by
pressing a button or using a remote control but many electrical
devices change their output by sensing their environment.
1. Write down as many environmental factors as you can that may be sensed by an electrical
device.
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
Light Dependent Resistors
2. Draw the circuit diagram for this experiment.
Pieces of tracing
paper
Resistance (kΩ)
1
2
Mean
0
1
2
3
4
5
3. What is the relationship between light intensity and resistance of the light dependent resistor?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
4. Write down as many uses of light dependent resistors as you can think of.
……………………………………………………………………………………………………………
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……………………………………………………………………………………………………………
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Thermistors
5. What do thermistors detect?
……………………………………………………………………………………………………………
6. Draw the circuit diagram for this experiment.
Temperature (oC)
Resistance (kΩ)
20.0
35.0
50.0
65.0
80.0
95.0
7. What is the relationship between temperature and the resistance of this thermistor?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
8. Draw a graph of temperature against resistance for this thermistor and stick it in here.
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9. A heating engineer wants to design his electronic circuit to switch on when the temperature
reaches 50 oC.
a) What is the resistance of this thermistor at 50 oC? Draw your construction lines on your
graph.
……………………………………………………………………………………………………..
b) Calculate the current that would flow through this thermistor at 50 oC. The thermistor
operates with a 2V potential difference across it.
……………………………………………………………………………………………………..
……………………………………………………………………………………………………...
...........................................................................................................................................
10. A reptile tank manufacturer wants to switch off the heater to a tank when it reaches 30 oC.
a) What is the resistance of this thermistor at 30 oC? Draw your construction lines on your
graph.
…………………………………………………………………………………………………….
b) Calculate the current that would flow through this thermistor at 30 oC. The thermistor
operates with a 2V potential difference across it.
…………………………………………………………………………………………………….
…………………………………………………………………………………………………….
…………………………………………………………………………………………………….
11. What range of temperatures was used in this experiment? ……………………………………….
12. What interval was used for the temperature? ……………………………………………………….
13. To what precision was the temperature measured in this experiment?
…………………………………………………………………………………………………………….
14. To what precision was the resistance measured in this experiment? Show your working.
…………………………………………………………………………………………………………..…
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15. Is the relationship between temperature and resistance inversely proportional for this
thermistor? Show your working.
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
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Mains electricity
On average, there are about 100 deaths due to electrocution annually in the
UK. This is because it only takes a small electric shock to kill a human being.
So, we have to be very careful when dealing with mains electricity.
Why A.C. electric shocks are so dangerous
1. What are the two main factors that affect how lethal an electric shock is?
……………………………………………………………………………………………………………...
2. What happens to the heart if an alternating current passes through it?
…………………………………………………………………………………………………………..….
……………………………………………………………………………………………………………...
......................................................................................................................................................
3. What size of alternating current can be fatal if it passes through the heart? ……………………...
Connecting to the mains
1. Label the parts of this 3-pin plug.
……………………...
……………………...
……………………...
……………………...
……………………...
2. What colour is the
a) Live wire? …………………………………………………………………………………………
b) Neutral wire? ……………………………………………………………………………………..
c) Earth wire? ……………………………………………………………………………………….
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3. What is the function of the fuse?
……………………………………………………………………………………………………………...
......................................................................................................................................................
4. What is the function of the cable grip?
……………………………………………………………………………………………………………..
……………………………………………………………………………………………………………...
5. Why is the earth pin longer than the live and neutral pins?
…………………………………………………………………………………………………………..…
…………………………………………………………………………………………………………..…
Which fuse to use?
When too much current flows through the fuse in a 3-pin plug the fuse wire gets hot, melts and
breaks the circuit. But how much current is too much current?
It’s easy to work out how much current should be flowing through a device and hence which fuse
should be placed in the plug. To work out how much current normally flows through a device use this
equation:
Current
=
(in amps)
Power
÷
(in watts)
Voltage
(in volts)
1. How much current normally flows through a 2000W kettle that works on mains voltage (230V)?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
…………………………………………………………………………………………………………….
2. Select the appropriate fuse to install in the plug for this kettle
1A
3A
5A
13A
3. Calculate the normal current flowing in a 690W microwave oven
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
…………………………………………………………………………………………………………….
4. Select the appropriate fuse to install in the plug for this microwave
1A
3A
5A
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Unsafe plugs
PLUG
Why is it unsafe?
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What needs to be done?
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Earthing
1. Through which two wires does current flow in and out of the device?
…………………………………………………………………………………………………………….
2. The diagram below shows the layout of a kettle with a fault where the earth wire is not
connected. The outer case of the kettle has now become live. If touched by someone they
could get electrocuted. Colour in red the route that the current takes when the person gets a
shock.
3. Redraw the diagram (smiley face this time) with an Earth wire connected to the inside of the
metal case. Colour the path that the current now takes in red.
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4. Why does the vast majority of the current flow through this path?
……………………………………………………………………………………………………………
…………………………………………………………………………………………………………….
5. What happens to the fuse when it ‘blows’?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
6. Why does the fuse ‘blow’ when there is a fault but not when the kettle is working normally?
……………………………………………………………………………………………………………
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7. Many devices do not require an Earth wire. Why not?
……………………………………………………………………………………………………………
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8. Devices with plastic cases are called ‘double insulated’. What do you think this means?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
Extension
9. Current flows into a device through the live wire and out through the neutral wire. Look at the
diagram of the kettle and explain why it is very dangerous to wire the live and neutral the
wrong way round.
……………………………………………………………………………………………………………
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Ed the electrician
Ed the electrician is a bit of a cowboy. He’s picked up a consignment of
dodgy cable from a shady character in a local pub at half price. When he
gets it back to his shed he finds that the cable only has two wires, the live
and neutral. When Ed goes back to the pub he finds that the bloke has
gone and nobody seems to know him. Ed paid in cash and knows that
he’s lost his money. Ed decides to use the cable for his wiring anyway.
Write a letter to Ed explaining the possible dangers of using this cable.
……………………………………………………………………………………………………………………
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A.C./D.C what does it all mean?
In this lesson, you will learn how mains electricity is different
from the electricity from cells. You will also learn how to
interpret mains traces and calculate peak voltages and
frequency.
1. What do the terms a.c. and d.c. mean?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
2. What is the difference between a.c. and d.c.?
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
3. Which type of current is supplied by mains electricity? ……………………………………………
4. Which type of current is supplied by cells? …………………………………………………………
5. Use the circuits below to describe how the potential of the live and neutral terminals in a 3-pin
plug vary.
L
N
L
N
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
6. Draw the traces to show how the live and neutral potentials vary through one cycle. Label the
axes.
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Frequency and peak voltage
1. What does frequency mean?
………………………………………………………………………………………………………………
………………………………………………………………………………………………………………
2. What is mains frequency? ………………………………………………………………………………
3. What is mains voltage? …………………………………………………………………………………
4. The frequency of a supply can be calculated using this equation
Frequency = 1/time period for one cycle
(in hertz)
(in seconds)
a) Label one time period (cycle) on the diagram below
b) If the time base setting is 0.10 seconds, calculate the frequency for this supply.
……………………………………………………………………………………………………………
……………………………………………………………………………………..………………………
……………………………………………………………………………………………………………
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Problems
1
An a.c. source is connected to an oscilloscope. The waveform of the alternating potential
difference from the source is displayed on the oscilloscope screen as below.
a) The Y-gain setting of the oscilloscope is 0.5 V/cm. Determine the amplitude of the alternating
potential difference.
..................................................................................................................................................
..................................................................................................................................................
b) The time-base setting of the oscilloscope is 0.02 seconds per cm.
i)
Show that the time for one cycle of the waveform is 0.06 s.
............................................................................................................................................
............................................................................................................................................
ii) Calculate the frequency of the alternating potential difference.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
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2
An a.c. source is connected to an oscilloscope. The waveform of the alternating potential
difference from the source is displayed on the oscilloscope screen as below.
a) The Y-gain setting of the oscilloscope is 2.0 V/cm. Determine the amplitude of the alternating
potential difference.
..................................................................................................................................................
..................................................................................................................................................
b) The time-base setting of the oscilloscope is 0.010 seconds per cm.
Determine the frequency of the alternating potential difference.
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
c) The a.c. supply is disconnected and a horizontal flat trace across the middle of the screen is
seen. On the screen above, draw the trace that you would expect to see if the a.c. supply
was replaced by a battery of p.d. 3.0 V.
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