# 01Modelling simple electrical loops

El01TA of the Electric circuits topic
• ## 01 Think again about electric circuitsEl01TAnugget01 Activity

### Pupils' initial thinking

What the activity is for

The questions are used for two main reasons:

• To encourage individual pupils to begin to think through their ideas about electric circuits.
• To provide the teacher with formative assessment information about the pupils' initial thinking.

What to prepare

• question sheets for think again questions 1–3

Support sheet

What happens during this activity

Pupils work individually or in pairs on the questions and are encouraged to think and to write down their answers with as much detail as possible. The questions might be set for homework prior to the first lesson so that you have time to read through the responses. Alternatively, they might be used at the start of the first lesson while you move around looking at what the pupils are writing.

• ## 02 Make or break!El01TAnugget02 Activity

### Using simple electric circuits

What the activity is for

This is a design and make activity through which you can review the idea of a complete circuit with the pupils and help them to build a circuit using the available laboratory equipment.

• To capture interest.
• To review the idea of a complete circuit.
• To engage pupils in designing and making circuits using appropriate laboratory equipment.
• To encourage pupils to talk and think about simple electric circuits.

What to prepare

• low voltage supplies, such as power packs or batteries
• buzzers and bells
• connecting wires, both 4 millimetre leads and insulated wire
• copper wire, copper strip, stiff card, plastic foam or sellotape

What happens during this activity

Start by demonstrating with a simple circuit containing a battery and a buzzer or bell that a complete circuit is needed for a buzz or ring. Then explain that the pupils are going to use this simple principle to design and make one of three devices:

• A burglar alarm for the classroom door: open the door and the bell rings.
• A pressure pad alarm: stand on the mat and the bell rings (or sit on the chair and the bell rings).
• A steady hand tester: touch the wire with the loop and the bell rings.

Divide the pupils up into teams of three or four and allocate a device to each team. Insist that the teams spend 10 minutes in talking through and drawing out their ideas before starting to work with the equipment. Equipment and materials should be set out so that the teams can collect whatever items they think will be useful. Be prepared for requests for additional items!

Allow plenty of time at the end of the lesson for each team to:

• Describe their invention.
• Explain how the device works.

To add to the sense of occasion, you might get some pupils to invite a senior member of staff into the lesson to try out the alarmed chair!

Experience has shown that the pupils really enjoy this activity and that it provides an excellent opportunity for talking around basic electric circuit ideas. Be prepared for pupils insisting that their door alarm is left in place, and then showing their friends from other classes how it works at break time!

• ## 03 The big circuit!El01TAnugget03 Activity

### Investigating a real circuit

What the activity is for

Having had the chance to think through their ideas aided by the diagnostic questions, the pupils are now shown a real circuit and are encouraged to bring their ideas out into the open through class discussion.

The big circuit consists of a power supply (battery) and bulb. The power supply is at the front of the room, the bulb at the back, and the connecting wires run right round the perimeter of the room, taped to the classroom walls.

Why use such a big circuit? The idea here is that the big circuit helps focus attention on the need for some mechanism to shift energy from the battery to the bulb and, most importantly, that the bulb lights very quickly, even when it is some distance from the battery.

What to prepare

• a mounted bulb (A 24 watt, 12 volt bulb works very well, being big enough for the whole class to see.)
• 12 volt power supply

What happens during this activity

First of all draw the pupils' attention to the size of the big circuit. They are actually sitting in the middle of it and: it's an absolute whopper of a circuit! With due ceremony, build up slowly to switching on the big circuit, asking the pupils to predict whether the bulb will light straightaway.

Teacher: What happens when the switch is closed?… Bulb heats up and lights up.

Teacher: Where does this energy come from in the first place?… The battery.

This happens pretty quickly, even though there is a big distance between battery and bulb:

Teacher: How does the energy get from battery to bulb?

Teacher: Why does it happen so quickly?

Teacher: We can see light being given out from the bulb and we can feel the heating effect, but we cannot see how this happens. What is going on in the big circuit to allow the bulb to light?

We think that in response to what happens with the big circuit, pupils will talk about electricity, electric current, charge flow and energy. These ideas can be built upon by developing a model for simple electric circuits.

View clip

Teacher: The aim of the next few lessons is for you to become experts in understanding and explaining how electric circuits work. Although we cannot see what is happening inside the wires and other parts of the circuit, scientists have a model to explain what is going on. We want to understand this electric circuit model.

• ## 04 From rope loop to electric circuit modelEl01TAnugget04 Activity

### Introducing the rope loop

What the activity is for

The rope loop is presented as a teaching model, which provides a way of helping pupils develop an understanding of abstract concepts (such as charge, current, resistance) by relating them directly to the movement of a length of rope around in a loop.

Notice how the same things are happening as in the electric circuit: a chemical store is being emptied (teacher as battery), and at a distance, something is getting warmed up (pupil as bulb).

What to prepare

• a long length of rope (6–9 mm diameter is ideal)

What happens during this activity

To introduce the rope loop model to the pupils the class is organised to stand in a big circle (you might carry out this activity in the school hall or outside) and the rope loop is passed out with each pupil allowing it to pass lightly over their curled fingers. The teacher (or nominated pupil) then starts to move the loop of rope round by passing it from hand to hand.

One pupil is instructed to grip the rope a little more tightly as it passes through their hand, and the teacher keeps the rope moving.

We have found it very effective to engage the pupils in this activity with little or no introduction, and then at this point (with the basic rope circuit set up) the teacher starts to pose questions:

Teacher: So! What has this to do with electric circuits? Any ideas?

The key features of the model to establish are that:

• The battery is represented by the teacher moving the rope.
• The bulb is represented by the pupil gripping the rope.
• The electric current (or moving charged particles) is represented by the moving rope.
• Energy is shifted through working (due to friction) at the bulb.

### Using the rope loop to establish the key features of the electric circuit model

The rope loop can now be used to consolidate the key features of the electric circuit model:

The charged particles originate in the circuit

Teacher: Now it's very clear. The rope isn't coming from me. I'm just making it move around. In just the same way, the charged particles don't come from the battery. It just makes them move around the circuit.

The charged particles all around the circuit are set into motion together

Teacher: Look everybody! As soon as I set the rope moving here, it starts moving all around the loop. In just the same way, as soon as the circuit is completed, the charged particles start moving in all parts of the circuit.

Current the same in each part of the loop

Teacher: The same amount of rope returns to me as leaves me every second. The rope does not get used up or disappear on the way round. In just the same way, the charge does not get used up on the way around the circuit, so the current is the same everywhere.

Energy is shifted where there is resistance

Teacher: Now Julia can feel her hands warming up because she is gripping the rope. There is warming due to the effect of friction as the rope passes through her fingers. No-one else feels any real heating effect because they are not resisting the movement of the rope.

We'd suggest that you link this back to the big circuit!

The point to make here is that it just does not matter how big the circuit is – unless it crosses the Atlantic!

As soon as the charged particles start moving energy is shifting from store to store.

• ## 05 Building and describing circuitsEl01TAnugget05 Activity

### Four foci for development

What the activity is for

We suggest you use very simple circuits here, to allow your class to concentrate on a restricted range of points:

• The energy in is equal to the energy out.
• Currents are the same through all elements.
• Charge flows are the same in all elements.
• Relationship between charge flow and current.

What to prepare

• the interactive

• a modern browser to run the swf files

What happens during this activity

Unzip the software and drag it to a browser window to launch the file.

One way to use this software is to build a small series of circuits, and then use the diagrammatic descriptions of energy, current, and charge flow to label them, respecting the relative magnitudes of these different, but related quantities. You will want your pupils to be confident in applying their understanding of the restricted range of points above before they move on to applying this understanding to more complicated arrangements of cells and lamps.

Some more specific suggestions:

Set up these four simple circuits and get the pupils to describe the energy shifts using the labels provided in the interactive.

For the same circuits, add different labels for charge flow.

Again for these circuits use a mixture of current and charge flow labels to set challenges. First increase the current and then get the pupils to alter the charge flow labels to match, or change the flow labels and get the pupils to match the currents.

This activity may be best for review using whole class discussion, or small group activities.

• ## 06 Questions on loopsEl01TAnugget06 Activity

### Three diagnostic questions

What the activity is for

The diagnostic questions can be used to check the pupils' understanding of key ideas introduced in this episode.

What to prepare

• paper copies of these three questions

Support sheet

What happens during this activity

The questions might be used for homework or as the basis for discussion in class.

The Electric current question probes the pupils' ideas about what is actually happening (unseen) inside the wires of the circuit. The best description of the electric current in the circuit is that there is an electric current in the wires connecting battery to bulb and the same current in the bulb and the battery.

The Electric charge question probes whether pupils think of charge as flowing out of the battery into an empty wire, or picture (correctly) the wire already full of charge that the battery sets in motion.

Answers: incorrect; correct; incorrect; incorrect; correct; correct.

The Charge and energy question probes the pupils' understanding of the difference between charge and energy. The question also serves to emphasise the importance of accurate use of the scientific terms involved.

• ## 07 Measuring electric currentsEl01TAnugget07 Activity

### Part 1: measuring what?

What the activity is for

Having introduced the basic elements of the electric circuit model, attention is now turned to measuring electric currents. It is important that pupils have an understanding of what it is that they are measuring when they measure the size of electric currents.

What to prepare

• 12 volt DC power supply
• 12 volt, 24 watt bulb in holder
• a demonstration rope loop, 3–5 m long and 5–9 mm in diameter

What happens during this activity

To help the pupils visualise what it is that is being measured, it is a good idea to start with a teaching model. Using the rope loop, draw your pupils' attention to the following points:

• As the rope moves round, all parts of the loop move at the same speed.
• The same amount (or length) of rope passes each point in the circuit in a given time.
• If a bigger push/pull is provided by the battery, more rope passes each point in a given time (as the rope all around the circuit moves more quickly).
• If a smaller push/pull is provided by the battery, less rope passes each point in a given time (as the rope all around the circuit moves less quickly).

You should make the link between:

Teacher: The amount of rope passing in a given time and the charge passing per second (current).

### Part 2: measuring how?

What the activity is for

The purpose of this part of the activity is to demonstrate how to use an ammeter to measure electric currents.

Teacher Tip: For this and other demonstrations we recommend using mounted 12 volt, 24 watt bulbs (car headlamp bulbs) with a 12 volt DC power supply and a demonstration ammeter.

What happens during this activity

Demonstrate how to connect the ammeter by talking through and demonstrating the following sequence with the pupils:

1. Make the complete battery/bulb circuit.
2. Teacher: So we make the connection from the positive side of the supply to the bulb and then from the bulb back to the negative terminal. Switch on and… hola!… the bulb lights.

3. Make a gap and connect in the ammeter.
4. Teacher: OK, switch off again. Now then! Where do you think the ammeter might go? Does it matter where in the circuit you connect it? Why? Now let's make a gap in the circuit where the meter is to go. So remove this lead and place the ammeter here.

5. Connect the ammeter the right way round.
6. Teacher: We then need to connect the ammeter the right way around. The ammeter has a positive terminal and a negative terminal. The positive terminal of the ammeter must be connected to the positive side of the supply.

### The ammeter goes in the circuit

Teacher: Switch it on, and the ammeter gives us the current reading. Every time you use an ammeter I want you to follow this same procedure. Make the circuit; make a gap in the circuit; and be careful to connect the ammeter the right way around.

Emphasising the point of making a gap in the circuit and placing the ammeter in the gap helps to promote an understanding of electric current measurement. All of the charged particles flowing around the circuit must pass through the ammeter. All of the passing charged particles are counted in the ammeter.

• ## 08 Predicting and measuring electric currentsEl01TAnugget08 Activity

### Measuring currents

What the activity is for

Having introduced what is involved in measuring electric currents, the pupils are now given the opportunity to make some measurements for themselves. This is an important practical activity for directly addressing the idea that the electric current does not get used up.

The approach taken is to encourage the pupils to think and talk about the electric circuit model and teaching model before taking the actual current measurements. To this end, the pupils are asked to make predictions of current values before they make each measurement.

What to prepare

• batteries
• bulbs
• ammeters
• support sheet: predicting and measuring currents

Support sheet

For the purposes of this activity, it is much easier for the pupils to use digital meters. Given the aim of establishing that the current is the same around each circuit, it makes sense to use less sensitive ammeters. It is not helpful for pupils to measure current to one-hundredth of an ampere and then to worry about differences between readings in the second decimal place. The scenario to avoid is:

Lizzie: Miss! The first was 0.72 ampere and the second was 0.73 ampere. The currents just aren't the same.

Avoid this by using an ammeter with a scale which reads to one-tenth of an ampere.

What happens during this activity

You might introduce this activity in the following way:

Teacher: OK, we have the idea that the ammeter measures the electric current and this gives us the amount of charge passing each point per second. If we measure the current here, and then here on the other side of the bulb, what would you expect to get?

Teacher: First of all, talk it through with your partner. Think about the electric circuit model with the charge moving round. Think about the rope loop. I'll give you a few minutes and then we'll talk through your ideas.

Teacher: OK, people are suggesting that the current should be the same in both places because the rope just keeps going round, or the charge just keeps moving round the circuit. As James says, none are added or lost.

Teacher: Well, collect the equipment and use an ammeter to measure the current values for yourselves. There are 3 circuits to investigate. Go to it!

For this activity, the pupils should ideally work in pairs and each pair has one ammeter, which is placed in the different positions in circuits A, B and C as shown on the support sheet. Some pupils may think that they need three ammeters for Circuit B. This is not the case!

As the pairs of pupils complete their measurements, it is a good idea to collect the current values on the board or on a large sheet of poster paper, so that the pattern of findings becomes apparent to all.

### The current stays the same

The current stays the same all of the way round each of the circuits. By this stage the pupils should have a clear picture of why this makes sense.

In terms of the electric circuit model:

The number of charged particles passing per second is the same all around the circuit. In the bulbs, energy is shifted but the charged particles keep going.

In terms of the rope loop:

All parts of the loop move around at the same speed (watch the red ribbon) as the battery sets it in motion.

Be sure to allow pupils to talk through these new ideas, as they review the current values for the whole class.

• ## 09 Building and predicting: current and charge flowsEl01TAnugget09 Activity

### Charge flow and current

What the activity is for

We suggest that you use parts of the circuits here to allow your class to concentrate on two aspects of the behaviour of circuits:

• Current does not get lost as it passes through circuit elements in series.
• Charge flows and currents are equivalent descriptions.

What to prepare

• this interactive object

• software to run the interactive on a class set of computers

What happens during this activity

One way to use this software is to build parts of circuits and then use the current and charge flow arrows to describe them. Pupils could be involved in setting the challenges or in doing the labelling, either as a whole class activity or working in small groups. In all cases, the class can use the precision of the diagrams to fix and discuss the relative magnitudes of currents and charge flows.

For these circuits, we suggest that you use a mixture of current and charge flow labels; then increase the current and get the pupils to alter the charge flow labels to match, or change the charge flow labels and get the pupils to match the currents. An alternative is to compare lots of elements: Here are four lamps with different currents. Add charge flow representations to match these pictures.

• ## 10 Questions on loopsEl01TAnugget10 Activity

### Questions on current

What the activity is for

The diagnostic questions can be used to check the pupils' understanding of key ideas introduced in this episode.

What to prepare

• copies of these three sheets

Support sheet

What happens during this activity

The questions might be used for homework or as the basis for discussion in class.

The Electric current at points question asks about the relative size of the electric current at two points on either side of a bulb. Some pupils may think that the bulb must use up some of the current.

1. The electric current is the same at a and b.
2. The current is the same all round the circuit.

The Battery and bulb question probes pupils' ideas about what is happening (unseen) inside the wires of a circuit.

1. There is an electric current in wire B from the bulb to the battery.
2. The current in wire B is the same as in wire A.

The Current motor question asks about the relative size of the electric current at two points on either side of a motor. Some pupils may think that a motor must use up some current (even if they think a bulb would not).

1. The reading on ammeter A2 is exactly 0.4 ampere.
2. The current is the same all around the circuit.
•