What the Activity is for

Throughout this practical activity, the pupils will establish that when an extra battery is added to a simple electric circuit, the current around the circuit increases in value and the bulb gets brighter; or the buzzer/bell sounds louder; or the motor turns more quickly.

What to Prepare

• batteries
• bulbs
• buzzers/bells/motors
• ammeters
• connecting leads
• support sheet: Adding batteries to the circuit

Support sheet

What Happens During this Activity

The pupils work in pairs to measure the current in the bulb circuit and buzzer/bell/motor circuit with one, two and possibly three batteries and observe what happens.

What the Activity is for

This activity can be used to explore the effects of adding extra cells to single loop circuits.

What to Prepare

• A copy of the interactive diagramming tool

What Happens During this Activity

Here you will want to concentrate on the two aspects of adding cells to the circuits, as experienced by the resistive elements in the circuit:

• There is more current in the elements.
• The energy shifted as each coulomb of charge passes through increases.

Other changes follow from this, and you may want to use the energy and charge flow descriptions as well, although these should not be central at this point. The whole circuit is important here, so we suggest building one or two simple ones, showing how the labels might be used, and then providing a few challenges to construct with the class as a way of fixing the behaviour of the circuit elements in their minds.

For simple loop circuits, we suggest that you use a mixture of current and voltage labels, and consider the necessary changes to these labels as the number of batteries is increased.

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

• printed copies of the questions

Support sheet

What Happens During this Activity

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

The question Which way around? targets the point that the direction that individual cells are connected in influences their effect on the circuit. Both cells need to be pointing in the same direction to provide a greater push on the charged particles, and to shift more energy to the charged particles as they pass through the battery.

• Circuit (b) is the brightest; the batteries are pointing in the same direction.
• Circuit (c) is the dimmest; the bulb will not light at all.
• Circuits (a) and (d) are of the same brightness; in circuit (d) two of the batteries are connected in the same direction, whilst the third is facing in the opposite direction.

The question Remove battery probes the way in which the current changes when the number of batteries in a circuit is reduced. When one of the batteries is removed, the current in the bulb gets less (but is not zero) because one battery exerts a smaller push on the charged particles.

The question Add battery probes the way in which the bulb brightness changes when the number of batteries in a circuit is increased. When an extra battery is added the bulb gets brighter because the extra battery pushes a bigger current around the circuit, and with the extra battery more energy is shifted by the charged particles.

What the Activity is for

Through practical activity, the pupils establish that when an extra bulb is added to a simple electric circuit, the current around the circuit decreases in strength and the bulb gets dimmer. They are then encouraged to make sense of their measurements.

What to Prepare

• batteries
• bulbs
• ammeters
• connecting leads
• support sheet: Adding bulbs to the circuit

Support sheet

What Happens During this Activity

The pupils work in pairs to measure the current through the circuit with one, two and possibly three bulbs and observe what happens.

Then pupils are encouraged to talk and think about the electric circuit model and teaching model to account for what they have found with the various electric circuits.

The pupils first of all work in pairs to talk through their ideas to explain why the bulbs are dimmer and the current smaller when a second bulb is added. Pairs then report back during class discussion.

What the Activity is for

Here you will want to concentrate on what is happening in the resistive elements of the circuit when bulbs are added to the circuits.

• Less current passes through the elements.
• The energy of each chunk of current is decreased.

What to Prepare

• set of batteries, bulbs and wires, suitable for building the circuits of your choice

What Happens During this Activity

(You might want to assume that doubling the number of bulbs in the circuit halves these quantities, as a first approximation.)

Other changes follow from this, and you may want to use the energy and charge flow descriptions as well, although these should not be central at this point. The whole circuit is important here, so we suggest building one or two simple ones, showing how the labels might be used and then providing a few challenges to construct with the class as a way of fixing the behaviour of the circuit elements in their minds.

For selected circuits, we suggest that you use a mixture of current and potential difference labels, and consider the necessary changes to these labels as the number of bulbs is increased.

Alternatively, you might seek to reinforce knowledge about the behaviour of charge flow by, for example, setting a question similar to the following:

Teacher: How can you picture the flow of charge in all of these circuits to give a fair comparison?

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

• printed copies of these four questions

Support sheet

What Happens During this Activity

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

The What happens to the current? question probes the effect on the electric current of adding a bulb to a circuit. When the extra bulb is added:

• The current in the circuit gets less, but does not fall to zero.
• The battery cannot push as big a current through two bulbs.

We find that many pupils incorrectly select the fifth option to explain what happens (the current is shared between the two bulbs, so each gets half). While it is acceptable to say that the energy is shared, it does not make sense to say that the current is shared.

This answer suggests that these pupils may not have separated in their minds the two distinct ideas of current and energy.

The Both ammeters question probes the effect on the electric current of adding resistance to a circuit. When the large resistance is placed in the circuit:

• The reading on ammeter A1 gets smaller.
• The reading on ammeter A2 gets smaller.
• This is because increasing the resistance makes the current smaller everywhere in the circuit.

The Two bulbs question probes the effect on bulb brightness of adding a second bulb to a circuit. When the extra bulb is added:

• Both bulbs are lit with the same brightness as each other.
• Energy is dissipated equally in the two bulbs as the charge passes around the circuit and the electric current is reduced everywhere in the circuit.

The Bright and dim question probes the pupils' understanding of what happens in a circuit with two non-identical bulbs when the current is reversed.

• The bulbs are the same as before. Bulb 1 is bright. Bulb 2 is dim.
• After turning the battery around, the current is the same (but reversed in direction) and energy is shared between the two bulbs as in the original circuit.

Some pupils may think that when the current is reversed, the brightness of the bulbs also changes over. Some pupils will be interested to talk through why bulb 1 is brighter (it must have a bigger resistance, so the rate at which energy is shifted is bigger in bulb 1).

What the Activity is for

This demonstration activity offers a way of helping pupils come to understand how parallel circuits work.

What to Prepare

• 12 volt, 24 watt bulbs
• 12 volt direct current power supply
• demonstration ammeter with a large, easy to read display

Using 12 volt, 24 watt car headlamp bulbs, a 12 volt lab-pack supply and a demonstration analogue meter (0–5 ampere direct current) you are likely to measure currents of 1.4 ampere in each loop.

What Happens During this Activity

Part 1: lighting two bulbs from one electrical supply

To start with, the teacher gathers the pupils around and, by way of review, demonstrates the familiar points that:

• One bulb connected to the supply is of normal brightness.
• Two identical bulbs connected in series are equally dim.

Then poses the question:

Teacher: How might you connect two bulbs to one supply such that both bulbs are of normal brightness?

Pupils are likely to suggest: Just connect up each bulb to the battery to make two circuits (and if they don't, you might offer: here's an easy way to do it).

Connect up the circuit and switch on. Both bulbs light to equal, normal brightness.

Seeing parallel circuits as two loops

At this point, with the bulbs there in front of the pupils' eyes, you should draw attention to the apparently odd nature of this circuit.

Teacher: So! Both bulbs light to normal brightness. I haven't added more batteries or anything else like that and yet we get two bulbs lit, twice the energy out. How can that be? It's the Yorkshire-man's dream: summat for nowt! What's going on here?

As a starting point to finding out what's going on, suggest measuring the currents in each of the circuit loops:

Teacher: Well, let's look at the currents in each of these loops. The big loop to the left and the small loop to the right.

Part 2: seeing parallel circuits as two loops

The next step is to re-organise the circuit so that it begins to look more like the standard parallel circuit format:

Teacher: Suppose I just lift this big loop across so that it fits around the small loop.

Focus on the current, then on the standard parallel circuit

Teacher: We have a current of 1.4 ampere in the small circuit coming from the supply, and 1.4 ampere in the big circuit, also coming from the supply. What, do you think, will be the total current from the supply?

The easiest way to measure the total current in the supply is to use two additional leads, from and to the supply, and to connect these to both loops. Measure the current in each of the two leads to the supply:

Teacher: So, the current from the battery here is 2.8 ampere and back to the battery here is 2.8 ampere.

The demonstration circuit now looks like the standard circuit diagram format for parallel circuits:

All that remains is to piece the explanation together.

Teacher: OK, so with one battery and one bulb, we can picture the charged particles moving through the battery around to the bulb and energy is shifted by each charge. When a second bulb is added in parallel, an extra loop is provided around which the charged particles move. The number of charged particles passing through the battery each second is therefore doubled, and the same amount of energy is shifted by each charge. So with the second loop the charged particles shift energy from the store associated with the battery at twice the rate and the battery will flatten more quickly.

What the Activity is for

This practical activity offers pupils the opportunity to build a simple parallel circuit and to take current measurements at various points around the circuit. The intention is to enable pupils to strengthen their understanding of how parallel circuits work.

What to Prepare

• batteries
• bulbs
• ammeters
• connecting leads

What Happens During this Activity

Pupils work in pairs to build a parallel circuit and to measure the current in the leads to and from the battery and through each of the bulbs.

Some pupils will benefit from large scale drawings of the circuits, so that they can place the physical elements directly on the drawings and so work out where to place the ammeters.

What the Activity is for

Here you will want to concentrate on the following two aspects of adding bulbs in parallel:

• There is more current in the battery.
• The energy shifted by each bulb remains constant, so long as there is only one bulb in each loop.

(You might want to assume simple proportionalities, as a first approximation.)

Other changes follow from this, and you may want to use the energy and charge flow descriptions as well, although these should not be central at this point. The whole circuit is important here, so we suggest building one or two simple ones, showing how the labels might be used, and then providing a few challenges to construct with the class as a way of fixing the behaviour of the circuit elements in their minds.

What Happens During this Activity

For selected circuits, we suggest that you use a mixture of current and potential difference labels, and compare the resultant changes to these labels as the number of loops is increased.

Alternatively you might want to set some circuits that bring together some of the challenges through this topic. For example, one could ask the pupils to build a circuit that flattens the battery twice as quickly. You could also ask for a circuit that flattens the battery at half the rate of the first one, so setting a harder challenge.

Again, use the labels to provide a set of reasons for this being a solution.

Much greater complexities are possible, for example: Build a circuit where three lamps are not all equally bright.

To develop this: Now add arrows to show the amounts of energy shifted by the lamps and the energy supplied by the cell.

And, even further: Now add arrows to show how much current passes through each bulb and through the cell.

So there are lots of possibilities for discussion foci here. You will need to choose wisely, with the abilities and interests of your class in mind.

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

• printed copies of these questions

Support sheet

What Happens During this Activity

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

The Same circuit? question is designed to probe pupils' ability to recognise equivalent ways of drawing a circuit with two parallel branches.

In fact, all of the circuit diagrams are correct representations.

The Identical resistors question probes understanding about the relative sizes of the electric current at different points in a parallel circuit.

CharList

The current at c is the same size as the current at b.

The current at d is the same size as the current at b.

The current at a is bigger than the current at b.

The current at e is the same size as the current at a. EndList

The Ammeter readings question probes whether pupils can apply their understanding of electric current to a parallel circuit.

Circuit a: A1 is 0.3 ampere Circuit b: A1 is 0.5 ampere; A3 is 0.3 ampere.