Electricity mastery bookletIntroduction: So what actually is electricity?

Electricity was not invented by humans. Electricity is a property of the universe. Ever since the first atmosphere formed on earth 5 billion years ago lightning has struck the earth. When the first multicellular life began to form 600 million years ago electrical signals were sent down their nerves to communicate to other parts of their bodies. Electricity is all about the flow of charges. Charges can be either positive or negative and when they move we are dealing with electricity. Electricity flows well down conductors, like metals and salty water, are poorly down insulators, like plastic and wood. Since the 1800’s scientists have been experimenting with electricity. We have managed to find ways of controlling the release, flow and direction of electricity by building circuits. This topic is all about understanding how electrical circuits work.

Lesson 1: Electrical circuits

The word circuit essentially means ‘looping path’. In an electrical circuit the electricity follows along a path made by the conducting material (normally a metal wire) in a loop until it returns back to the start. The starting point could be a power pack, which is connected to the mains electrical supply, or a battery. A battery is made from more than one cell. This is the same word as used in biology for animal and plant cells, but it is a very different object. An electrical cell is a small packet of chemicals which can release and electrical current when the ends are connected. Circuits are complex and each part, or component, can look very different depending on who manufactured it. So we use a set of circuit symbols to make sure everyone knows what a circuit diagram is trying to show.

Here are the circuit symbols you need to know, they will never change.

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1. Give two natural examples of electricity2. Name 2 insulators3. Name 2 conductors4. Give 2 examples of sources of electricity5. Why do we need to use circuit symbols?6. Draw the symbol for a cell and a battery. Explain how they are similar and different to each other7. What store of energy is inside a cell or battery?

Building circuits practicalBuilding circuits by following the circuit diagram is an important skill. Look closely at the diagram and build the circuit.

Make the simple circuit shown on the right Check that all your equipment is working

8. What happens to the bulb when you use fewer cells in the circuit?9. What happens to the bulb when you use 2 cells in the battery, but

add more bulbs in the circuit?10. What happens to the bulb when you use 2 cells and 2 bulbs, but

carefully unscrew one of the bulbs from its holder?11. Which of the following will give the brightest bulb? Make sure you give a reason for your answer.

A B

C D

Explaining electrical circuits using models

The charges that move in electrical circuits are incredibly small and impossible to see, but their effects and the rules they follow are visible and predictable. To help us understand these ideas we use a model, or analogy, to explain what is happening. The model is never perfect, but it gives us something to visualise to help us understand. Electricity uses three types of model, the rope model, virtual simulations and the coulomb train model.

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Using the coulomb train modelLook at the picture to the right. In this model the electrical circuit is thought to be made of a continuous chain of train trucks. Each of these is called a coulomb. A coulomb is the unit electrical charge is measured in. The trucks leave the battery full of energy. As they travel clockwise around the circuit they transfer that energy to the bulb, which transfers it on to the surroundings, before returning to gain more. This process can go on again and again until the battery has no more energy left to transfer.

12. Complete the table below, The first one has been done for you

What happens in an actual circuit What happens in a coulomb train model

The electrical charges (electrons) flow The trucks move around the track

The battery increases the energy of each coulomb

The trucks travel on a track

The bulb transfers energy from the coulombs

The electricity appears to work instantly

Eventually there is no energy left to fill the trucks

13. By looking at the diagram on the right and the

coulomb train model answer the following questions in your book in full sentences.

a) Explain why when the wire is connected to the battery the bulb lights up

b) State what you could do to increase the brightness of the bulb. Explain why this would work

c) If the circuit is left on why will the battery eventually go flat.

13. Draw the circuit symbol for an open switch

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14. Draw a circuit symbol for a cell15. What is the difference between a cell and a battery? 16. Judith has built a circuit. She has followed the diagram correctly but the bulb is not lit up. Describe what

she could do to check the circuit and get the lamp to work. Hint: there is more than one answer.17. Draw a circuit diagram that has 2 cells a switch and 2 bulbs in one loop

Lesson 2: Electrical current in a series circuit.

So far we have built circuits and observed a bulbs brightness. We know from the coulomb train model that the ‘trucks’ called coulombs carry the electrical energy to the components of the circuit, like the bulb.People have been interested in how many coulombs of electrical charge flow through the circuit in a second. A French scientist called Ampere invented a machine called an ammeter which allows us to measure the number of coulombs that pass a point in a second. 1 coulomb per second is called 1 amp. It is given the letter I, because in French its referred to as intensity of current.In our coulomb train model we can imagine the ammeter to be able to count the number of trucks that pass a certain point in a second. It can’t tell us how much energy they contain just the rate of flow.

18. What is the job of an ammeter?19. What is the circuit symbol for an ammeter?20. Can an ammeter tell you how much energy is stored in each coulomb?21. What component causes the coulombs to flow?22. Which circuit has faster flowing coulombs of charge? Circuit A with a current of 3 amps or Circuit B with 4

amps23. What about if circuit B was twice a long? Explain your answer.

Series circuitsSeries means ‘one after another’. For example, in a TV series, episode 2 follows episode 1 and they should be watched in order. In a series circuit all the components are in one loop. If you look at all the circuits, we have built so far they are all series circuits.

Investigating current in a series circuit.Please only record readings to 1 decimal place.Series CircuitsSet up this circuit, put your ammeter where it says “A1”, then “A2” etc, and WRITE DOWN the readings:-

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Additional ComponentsNow add another bulb to your circuit as shown below:

24. What can you tell from experiment 1 about current in a series circuit?25. Does the current change if you have more, or fewer bulbs in the circuit? 26. Why does this happen?27. What do you notice about the brightness of the bulbs in the circuit?

Explaining the findings using the coulomb train model. It is very easy to see why the current is always the same in a series circuit. As all the ‘trucks’ are on the same track they all have to pass through the ammeter no matter where it is positioned. So, in the diagram to the right I3, I4

and I5 are all the same.

28. How does the current change around a series circuit?

29. Austin says; “the current after the second bulb will be less because the bulb has used some up.” Is he correct? Give a reason.

30. Is the ammeter connected in series with the circuit?

Lesson 3 Current in parallel circuits

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In a parallel circuit the components are not all in the same loop. Below shows the difference between the two types of circuits.

Investigating the current in parallel circuits

Set up the circuit as shown below. Measure the current by adding an ammeter to one position at a time. Record the current next to each diagram below.

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31. What is the link between the values of I6, I7 and I8

32. Susan was measuring the current in a similar circuit. She recorded a value of 0.8 amps next to the first bulb and 0.9 amps next to the second bulb. What was the current by the cell?

33. Geoff was also working on the same circuit. He said; “the readings must be wrong because the current should be the same all the way round a parallel circuit.” Is he correct? Give a reason.

Explaining the rules for current in a parallel circuitWe need to change our coulomb train model slightly to explain how a parallel circuit works. We now need to have two tracks. On both tracks it does not matter if we measure before the bulb or after, but crucially the ammeters by the bulb (I6 and I11) can count both tracks so their value will be the total of the two tracks.

To summerise:

In a parallel circuit the current is shared between

the separate loops

In a series circuit the current is the same at any

position.

Do the two loops have to have the same current?

A common misunderstanding is that if the total current is two amps then the two loops must have one amp each. This is only true if both loops contain identical components. This is because of an idea called resistance. In our circuit as the coulombs flow, they must do work to move. This slows them down slightly and wastes energy. In our coulomb train model, we can think of this like the trucks slowing down as they reach the ‘tunnels’ of the bulbs. If the ‘tunnels’ are the same, i.e. the bulbs resistance is the same then they will each go at the same speed. But if one ‘tunnels’ is narrower then the trucks will have to slow down more. In the circuit we would say that one bulb has a greater resistance than the other. No matter what is on each loop. The total current by the bulb will be the same as the two loops currents added together.

34. What is the rule for current in a parallel circuit?

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35. Copy and complete these sentences:Current is always shared in a parallel circuit because….Current is always shared in a parallel circuit but…..

36.(a) Draw a line from each electrical circuit to the correct circuit diagram.

Draw only four lines.

electrical circuit circuit diagram

(b) In each circuit below, bulb 1 breaks and goes off.

Under each circuit diagram below, tick the correct boxes to show if bulb 2 andbulb 3 are on or off.

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circuit A circuit B

2 marks

(c) Give the name of the part that provides energy for each circuit.

........................................................1 mark

maximum 6 marks

37. Peter measured the current through each of three similar bulbs in a parallel circuit.

He had only one ammeter and he placed it first at A1, then A2, then A3, in order to measure the currents.

The table shows his results.

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position of ammeter current, in amps

A1 0.14

A2 0.16

A3 0.15

(a) He expected the current readings to be the same for each bulb but found they were different.

Suggest two reasons why the readings were different.

1. ................................................................................................................

2. ................................................................................................................2 marks

(b) Peter then measured the current at A4 and recorded it as 0.45 A. He concludedthat the current at A4 could be calculated by adding together the currentsthrough each of the bulbs at positions A1, A2 and A3.

He added two more similar bulbs to his circuit, in parallel. The current througheach bulb was 0.15 A.Use Peter's conclusion to predict the current at A4 with the 5 bulbs in the circuit.

................ A

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1 mark

(c) Peter left the circuit connected overnight. He used a datalogger to measure the current at position A4 at regular intervals of time. The next morning the bulbs were dim.

Using the axes below, sketch (do not plot) how the current at position A4 mightchange with time.

Indicate on the graph:

(i) The correct labels for each axis, including the correct units.

(ii) The shape of the graph you would expect to obtain.

Lesson 4 Potential difference and cells

So far we have managed to answer a number of questions about electricity involving current, but we have yet to explore ideas around the energy in the coulombs. You would have noticed that during our series circuit

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experiments the bulbs got dimmer as more bulbs were added. To measure how much energy is transferred to a bulb we need to measure the energy each Coulomb has before the bulb and after it. This difference in energy is known as the potential difference (p.d.) or voltage. It is measured using a voltmeter and given the unit volts, V. 1 volt means 1 coulomb is transferring 1 joule of energy. Because we need to measure a difference a voltmeter is always connected in parallel to a component you are investigating

NOT

Potential difference is provided by the cell, which also provides the push that creates the current we have previously measured. Voltage follows opposite rules to current in series and parallel circuits.

In a series circuit the voltage is shared between each component. If you look to the right as the trucks move clockwise from the cell, they are full of energy. When they meet the first bulb, some of the energy is transferred (the difference will be the voltage V4) They then carry through the second bulb and transfer the rest of the energy (the difference here is V5 in the diagram)So the potential difference of the cell is equal to the sum of the potential difference of each component.

Total V = V4 + V5

In a parallel circuit the voltage is the same on each loop. This is because as the current is shared each coulomb (truck) only passes through one loop so transfers all its energy to that component. So, in a parallel circuit the potential difference of the cell and the components are equal Total V = V4 = V5

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Investigating potential difference Build the circuits shown in the diagram and write the voltages next to each voltmeter

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38. State another word that means potential difference.39. Is a voltmeter connected in series or parallel to a component?40. How much energy per coulomb is 1 volt?41. What is the rule for potential difference in a series circuit?42. What is the rule for voltage in a parallel circuit?43. Complete the table below to summarise the way potential difference and current behave in a series or

parallel circuit.

Series Parallel

current

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p.d.

44. What is the potential difference V2 in the following circuit? Give a reason for your answer.

45. What is the voltage V1 in the following circuit? Give a reason for your answer.

46. Find the input voltage Vin. Give a reason for your answer.

What are the missing values? How do you know?

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47. What are the missing values? How do you know?

48. What are the missing values? Give a reason

What effect des adding more cells have?Each cell will have its own potential difference. This will be the amount of energy it can transfer to each coulmb and also how much push it can contribute to the current. If we add another cell to a battery then we just add the voltages together. So if I place 3 1.5V cells together in my battery I have a potential difference of 4.5V.

49. The lamps in the circuits drawn below are all identical.Each of the cells has a potential difference of 1.5 volts.

(i) What is the potential difference across the 3 cells that are joined in series?(ii) What will be the reading on the voltmeter labelled V3??(iii) Which voltmeter, V1, V2 or V3, will give the highest reading?

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50. Complete the sentences below:A voltmeter is always connected in parallel because….A voltmeter is always connected in parallel but….A voltmeter is always connected in parallel so we can use it to…

Lesson 5: Resistance and ohm’s law

We have touched on resistance earlier in the topic. When charges are pushed through components, particles inside the components get in their way. This obstruction is called resistance. The symbol for resistance is R and the unit is Ω (ohms). 1 ohm of resistance means you need 1 volt of p.d. to make a current of 1 amp flow through the componentResistance splits up the potential difference in a loop of a circuit. As you follow a circuit round from the positive terminal of the battery, components with resistors are like steps in the potential difference. The higher the resistance, the harder it is for the potential difference to push the charges through the component.Resistance is not measured directly but is calculated by measuring the potential difference across, and the current through, a component, and then using the equation called ohms law. Some materials always have the same amount of resistance, we call these fixed resistors.

Ohms law

Resistance= VoltageCurrent

or in symbols R=VI

51. What causes resistance?52. What do we used to measure the potential difference across a component?53. What doe we use to measure the current through a component?54. Which of the two meters used above is connected in series?55. What is the symbol used to represent current?56. What is the unit of current?57. What is the symbol used to represent potential difference?58. What is the unit of potential difference?59. What does the resistance of each component do to the p.d. in one loop of a circuit?

Hypothesis:The current flowing through a resistor is proportional to the potential difference across it. Independent variable:…………………………………………………………………………………………………………………………………………..

Dependent variable:………………………………………………………………………………………………………………………………………………

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Key Stage 3 Required Practical:Ohm’s Law

Method:1. Set up the circuit as shown in the diagram below. Use a resistor of known value.

Pd across the resistor (V) Current in the circuit (A) Resistor used(Ω)

2. Turn on the power pack, take readings from the ammeter and the voltmeter and record them in the table. 3. Increase the pd on the power pack and repeat. 4. Keep going until you have at least 5 readings.

Results

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60. What relationship can you see between pd, current and resistance?61. What relationship can you see between pd and current?62. Do your results support your hypothesis? Use data to back up your statement. 63. Sketch the pattern you would expect to see if you plotted the data on a graph.

Using Ohms law to calculate resistanceRemember in all calculations you must show your workings

64. Worked/Partial example 1: calculating potential difference (voltage)

Worked example: Find the potential difference that will push 2.4A of current through a 90Ω resistor.

Partial example: Find the potential difference that will push 5.2A of current through a 40Ω resistor.

Equation

Values

Enter values

Result

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(Y)units

65. What is the potential difference needed to create 14A of current through a 12Ω resistor?66. Calculate the voltage if a 10Ω resistor has 0.5 amp of current flowing67. What voltage will let 5 amps flow through a 0.5Ω resistor?68. A 2.5Ω resistor is connected to a circuit that has 0.25 amps flowing. Calculate the p.d. of the resistor.

69. Worked/Partial example 2: Calcualting resistance

Worked example: Find the resistance of a component which allows 25A of current to flow when 100V of potential difference is put across it.

Partial example: Find the resistance of a component which allows 5A of current to flow when 25V of potential difference is put across it.

E

V

E

R

(Y)

70. What is the resistance of a resistor with 680V of potential difference across it if 46A of current are flowing?

71. What resistance will be caused by a lamp that has 3 amps flowing when a voltage of 9 volts is applied72. Calculate the resistance of a circuit which has a potential difference of 4.5V and a current of 3 amps73. A resistor has a potential difference of 5.5V and a current of 0.5A what is its resistance in ohms?

74. Worked/Partial example 3: Calculating current

Worked example: A battery gives a potential difference of 12V. Find the current through a resistor of 30Ω connected directly to the battery.

Partial example: A battery gives a potential difference of 4V. Find the current through a resistor of 20Ω connected directly to the battery.

E

V

E

R

(Y)

75. Calculate the current flowing when a 45Ω resistor has 20V of potential difference across it. 76. A 50Ω resistor has a voltage of 25V. What is the current flowing?77. Calculate the current flowing through a 10 Ω resistor when a potential difference of 3.3V is applied

Mixed practice

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Note on units. When numbers are very big or small we change the units to make them easier to read.

Unit Change to the number

M (mega) X 1,000,000

K (kilo) X 1000

No change No change

m (milli) ÷ 1000

µ (micro) ÷ 1,000,000

78. The voltage across a lamp is 12 V and the current through the lamp is 2 A.

Calculate the resistance of the lamp?

79. The current through an ipad is 0.1A and the voltage of its power supply is 12V. Calculate the ressistance of the ipad?

80. The resistance of a resistor is 34 Ω and the current through it is 0.3 A. What is the voltage across the resistor?

81. The voltage across a 50 Ω resistor is 6 V. What is the current through the resistor?

82. The resistance of an iPhone is 3 kΩ and the current through it is 4 mA. What is voltage of its power source?

83. The voltage across a woman when she is struck by lightning is 33 MV and the resistance of a human being is around 1 kΩ. What current flows through the woman?

84. For the circuit 1, above, calculate the current that will flow in the circuit.

85. For the circuit 2, above, calculate the current that will flow. Lesson 6 Why do some things have higher resistance than others?

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Circuit 1

Circuit 2

So far, we know what resistance is, how to measure it and how to calculate it. But we don’t know what makes something have a different resistance to something else. Resistance is affected by a lot of different factorsWe can use our coulomb train model to explain how these features affect the resistance. A smaller cross section is a narrower tunnel causing the trucks to slow. The longer the tunnel the slower the trucks will be moving and the more densely the particles of the wire are packed the harder the coulombs find it to flow. This is like if the track was rougher or uphill.

Investigating how the length of wire affects the resistance

The independent variable is _________________________________________________________

The dependent variable is __________________________________________________________

Method:

Set the circuit up as show

Set the crocodile clips 10 cm apart

Turn on the power pack

Record the potential difference and current

Turn the power pack off

Repeat the process for different lengths of wire

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ResultsLength of wire (cm) Voltage (V) Current (A) Resistance (Ω)

86. Plot a graph of length of wire on the x axis and resistance on the Y axis. Draw a straight line of best fit.87. Write a conclusion by completing the sentences below

As the length of wire increases the resistance…I know this because in my data….

88. The diagram shows the circuit set up by a student.

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(a) The student uses the circuit to test the following hypothesis:

‘The current through a resistor is directly proportional to the potential difference across the resistor.’

(i) If the hypothesis is correct, what should the student predict will happen to the current through the resistor when the potential difference across the resistor is doubled?

(ii) Name the component in the circuit used to change the potential difference across the resistor.

(b) The student used the data obtained to plot the points for a graph of current against potential difference.

(i) Why has the student plotted the points for a line graph and not drawn a bar chart?

(ii) One of the points has been identified by the student as being anomalous.

What is the most likely cause for this anomalous point?

(iii) Draw a line of best fit for these points.

(iv) Does the data the student obtained support the hypothesis? Give a reason for your answer.

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Lesson 7: What happens when charge cannot flow?

In all our experiments and studying of electricity it has been flowing through circuits. But this is not always the case. Electricity can flow through conductors because they allow the charges to move. Insulators do not allow the charges to move, but this does not mean they cannot experience charge. If a charge occurs on an insulator it cannot flow. It is static, which means ‘not moving’. This is static electricity. It can be incredibly useful and dangerous. It can get up to incredibly high potential differences, for example static electricity in clouds can create lightning with voltages around 1 billion volts!

How static charges build upThe key to understanding how static builds up is friction. When two different insulators rub together the electrons in their atoms can move. The electrons will move from one insulator to the other. The electrons are negatively charged so the insulator that loses electrons will become positively charged and the insulator that gains them will become negatively charged.The charges begin to build up as they cannot move and the potential difference increases. When the charges are brought close to each other or a conductor they can begin to flow. The earth is a large supply of electrons and often charges will ‘jump to earth’. This is often seen as a spark or felt as an electric shock. You may have experienced this when going on a trampoline, or touching a metal door handle when walking on a carpet.

89. Complete the diagram below by adding labels from the text above

90. Why is it called static electricity?91. Why can you build up static electricity by rubbing a balloon on a jumper?92. What force pulls the electrons off an insulator?

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The charges that build up follow very specific rules, much the same as magnets.

So oppositely charged insulators will attract and same charged ones will repel. This is incredibly useful. In a photocopier the black powder is oppositely charged to the paper so they stick together and in cling film the top and bottom are oppositely charged so it sticks to itself.

93. Define insulator and conductor94. What will happen to positively charged hair near a negatively charged ruler?95. What force causes static electricity to build up?96. What sub atomic particle is transferred when static electricity builds up97. Ameera is rubbing a copper pipe with a dusting cloth. Will she create a static charge? Give a reason fr your

answer98. I am walking in my hall way wearing a new pair of slippers. When I get to the door I get a shock as I go to

touch the metal handle. Write a simple paragraph to explain why I got a shockKey words: static, friction, electron, insulator, conductor, transfer

Lesson 8: Magnetism

Magnets are amazing. Magnetic materials work because each of the materials atoms is a tiny magnet. Often these magnets are all randomly arranged so the object, say a nail, it not magnetic. If we rub a magnet along the nail it

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will pull all the atoms, so their tiny magnets line up. When this happens, the nail becomes a magnet. Each magnet has a north and a south pole and these follow the same rule ‘opposites attract’ as charges. Magnetism is a non-contact force, like gravity. This means it can work at a distance and is invisible. The earth has a magnetic field due to its spinning iron core. Compasses are also tiny magnets that allow us to plot the magnetic field lines so we can see them. The closer the lines the stronger the force.

99. What happens to the following magnet pairs? Do they attract or repel?

100. What is a non-contact force?101. How can we see the invisible line of a magnetic field?

Magnetic fieldsWe can use a plotting compass to show the field lines of a magnet. Place the magnet in the middle and draw an arrow to show the way the compass points at each space.

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102. Which of these materials would be attracted to a magnet? Circle your answer i. An iron bar

ii. a gold ringiii. a 2p coin (made of copper and nickel)iv. A plastic spoon

103.Will these pairs of magnets attract or repel each other? Write ‘attract’ or ‘repel’ underneath each pair.

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a N S S N b N S N S

c S N S N d S N N S

104.a Draw in four magnetic field lines around the bar magnet. Label where the field lines are strongest.

S N

b This magnet has a stronger field than the magnet in a). Draw field lines around it to show that it is stronger.

S N

Lesson 9: Electromagnets

So far, the magnets we have used are permanent magnets, they are always magnetic. Sometimes it is much more useful to have a magnet that we can turn on and off. The are called electromagnets. Electricity and magnetism are linked together as a force called electromagnetism. This means that when an electric current flows through a conductor a small magnetic field is generated. We can make the electromagnet stronger by turning the wire into a coil (called a solenoid) and by introducing an iron core.

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105.What is the difference between an electromagnet and a permanent magnet?

106.What causes the magnetic field in an electromagnet?

107.Why does the wire of an electromagnet need to be insulated?

108. Label this diagram

109. What would happen to the magnetic field if the cell ran out?

Investigating a factor that affects the strength of an electromagnet.

You will be designing an investigation in your books. There are many things we could change that would affect the strength of the electromagnet:

The number of turns in the solenoid

The voltage of the power pack

The width of wire used

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The material used in the wire

Our hypothesis we are going to investigate is:

“Increasing the voltage will increase the strength of the magnet”

110. From the list above name the independent variable of the investigation

111. From the list above state 2 control variables we will have to keep constant

112. The dependent variable is….

Range and interval

The range of the independent variable is the minimum and maximum values used. The interval is the value we increase the variable in. in our investigation The maximum voltage we will use is 6 volts. This is to prevent overheating. The minimum voltage we will use is 1 volt.

113.What is our range of our independent variable (volts)?

114.What is the interval for our independent variables?

Results and repeats

We will do three repeats and take a mean, so our results table needs to have enough space to fit the results in.

In general the independent variable goes on the left most column. The dependent variable goes on the middle columns and the mean goes on the right.

Independent variable (unit)

Dependent variable (unit)

Repeat 1 Repeat 2 Repeat 3 Mean

115. Use the guide above to draw a neat results table in your book. Instead of writing ‘independent variable’ you should write our independent variable and its correct unit

Conclusion

116. What happened to the number of paper clips your magnet could hold as the voltage increased?

117. Explain why this happened using the following key words: current, magnetic field, stronger

118. Were there any anomalous results?

119. Are your results reproducible? (Hint: look at another groups data)

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Lesson 10: Electromagnetic devices

Electromagnets are used in many ways. Below is a table that summarises some of the uses and how they work. Read them carefully.

Use How electromagnets are involved

Electric bell When the switch is pressed a current flows through the electromagnet. This attracts the armature. The hammer hits the bell. This causes the contact to break and the electromagnet switches off. The hammer returns to the start and the circuit is remade. So the armature is attracted making the hammer hit a second time. The process continues until the switch is turned off.

Electric Shower

When you switch on the electric shower you are only switching on a low current circuit. This turns on an electromagnet which moves a switch called a relay. The relay is a switch to a high voltage circuit which powers the pump. Because you are not touching the high voltage circuit there is less chance of electrocution.

Scrap heap Because electromagnets are able to be switched off they can be used to pick up scrap metal and then drop it into recycling.

Fire safety doors The safety doors need to be held open most of the time. So, they are connected to the electromagnets that have an electric current running through them. When the fire alarm is activated the circuits to the door holders is switched off automatically. This turns off the electromagnets and the springs on the doors closes them.

Tag removers Shops have special tags which prevent theft of products. When you buy an item the assistant places

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the tag in a release box. Inside the box and electromagnet is switched on which unlocks the tag allowing it to be removed

Maglev Trains Short for ‘magnetic levitation’ the maglev runs on a cushion of electromagnets. This means there is mush less friction with the tracks. The trains can travel much faster

120. What is the most important feature of electromagnets?

121.Explain how the electric bell can make multiple rings when you push a door bell.

122. How does a relay switch prevent you getting electrocuted in the shower?

123. Why does a scrap metal crane not allow you to pick up an aluminium bike frame?

124. What will happen to the fire safety doors if there is a power cut? Explain your answer.

125. Why might a criminal bring a large magnet into a shop?

126. When the train is fully of passengers the electromagnets need to have a greater current flowing through them. Suggest why.

The electric motor

The electric motor is probably the most important use of electromagnets. Think of all the things that have electric motors in from cars to toothbrushes. They are a valuable technology.

A simple electric motor works by placing a coil of wire inside a magnetic field created by a permanent magnet. When a current flows through the wire it creates an electromagnet. The current flows in the direction that makes the electromagnet have the same poles as the permanent magnet. This makes it repel and it begins to turn, this is called the motor effect. As this happens the current changes direction, due to the device called the brushes, and the electromagnet poles switch. The result is that the coil is always repelled by the permanent magnet. This makes the motor turn incredibly fast.

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127.Describe the energy transfer in an electric motor connected to a cell128.What does a motor consist of?129.What is produced by the current in the wire?130.What causes the wire to move?131.What is this movement called?132.How can we make the coil of wire spin faster?133.Label the diagram below:

RevisionMisconception/inaccurate language Correct statement

The current is the flow of electricity

The voltage is the energy that the current gets

Resistance is what stops the current for a given voltage

Metals are magnetic

Metals can be given a static charge by rubbing them

Voltage causes a magnetic field in a wire

Field lines travel from south to north poles

A stronger magnet has thicker field lines

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Electricity Revision quiz

134.What moves in wires to give a current?

135.What provides the energy for this to happen?

136.Why do bulbs light up when the charges move through them?

137.Draw the symbol for a bulb and a cell.

138.What is current?

139.Describe the pattern of current in a series circuit

140.What are the units for current?

141.How is an ammeter connected into the circuit?

142.Explain what happens to the current when we put additional components in a series circuit?

143.What is a parallel circuit?

144.What happens to current in a parallel circuit?

145.What happens if there is less resistance in one of the strands?

146.What do we call a circuit where one of the strands is such low resistance that all the current flows through there, and not through any components

147.Describe the pattern of voltage in both series and parallel circuits

148.What is resistance?

149.What is the unit for resistance?

150.How does adding extra bulbs affect resistance?

151.When the resistance is high, what happens to current?

152.What is the relationship between current, pd and resistance?

153.What causes a static charge?

154.What is transferred when a static charge is created?

155.Which metals are magnetic?

156.In which direction do magnetic field lines go?

157.How do the field lines tell you the strength of a magnet?

158.Why does compass point north?

159.Where will the magnetic field of the Earth be strongest?

160.What do we call the variables that we change, measure and keep the same in an investigation?

161.Name two factors which affect the strength of an electromagnet?

162.How is an electromagnet different to a bar magnet?

163.How do the field lines tell you the strength of a magnet?

164.What is induced (created) when a current passes through a wire?

165.How do we increase the strength of an electromagnet?

166.What do we mean by a non-contact force?

167.What do the field lines tell you about the strength of a magnetic field?

168.What do we place in the coil of wire to increase the strength of an electromagnet?

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