The jelly bean role play (vignette)

The Jelly Bean role play – some pros and cons

Many teachers like using the Jelly Bean Role Play as an approach to teaching about electric circuits. In the role play, two students are assigned the roles of ‘battery’ and ‘light globe’.

The ‘battery’ is given a bag of jelly beans which represent ‘energy’. The ‘battery’ and the ‘light globe’ stand about 3 or 4 metres apart.

About 10 more students act as ‘movable charged particles’, and are asked to form a complete ‘circuit’ between the ‘battery’ and the ‘light globe’. After a direction for the ‘current’ has been agreed upon, the ‘movable charged particles’ start to move around the ‘circuit’.

As they pass the ‘battery’, the ‘movable charged particles’ are handed two jellybeans which they then give to the ‘light globe’ as they pass it. The ‘light globe’ eats the jelly beans and then does something (e.g. waves his/her arms) to represent the action of a real light globe producing heat and light.

The role play is intended to show that that in an electric circuit containing a single battery and light globe, the battery supplies a constant amount of energy per charged particle and that this energy is transferred to the light globe where it appears as heat and light.

Students generally find the role play to be fun – especially if they get to eat the jelly beans! – and, once completed, often feel that at long last they have finally begun to understand electric circuits. In this PaP-eR, an experienced science teacher shares with a beginning science teacher some of the pros and cons of this role play in terms of student learning.

Some pros

Mr Hall, who was halfway through his first year of teaching, was talking to Ms Smith, an experienced physics teacher, about ways of teaching a unit called ‘Electric circuits’ to his Year 10 general science class that he was planning to begin the following week. “I’ve heard that kids love the Jelly Bean Role Play that is suggested in the course guidelines. They find it such a change from sitting down all the time and, and of course, there are jelly beans to eat into the bargain.”

Ms Smith smiled. “Yes, students do enjoy it. And it does help develop their understanding of some science ideas about circuits although I’ve found that if I’m not careful, it can give them ideas that I have to ‘unteach’ later!”

“Really? Have you got time to talk about how you use the role play? The ideas in electric circuits seem so complex and I was thinking that it looked like a good way of developing students’ understanding.”

“Mm,” Ms Smith responded, “Well, recognising the ideas are complex is a good start! I think it’s important to give the students a couple of periods for playing around with a few simple circuits first because many of them have very little prior experience with circuits, beyond turning on the light switch at home or inserting some batteries into the latest electronic gadget. So I give them an activity designed to help them understand how to make a complete circuit – in other words, how to connect up a battery and a light globe so the light globe lights up. I also give them some activities that explore how to change the brightness of a light globe in a circuit. Like what happens if you’ve got a circuit containing one light globe and a battery, and you connect an extra battery or you add an extra globe in series. After the class has got the idea that adding a battery makes the globe brighter whereas adding another globe in series makes it dimmer, they are ready to start thinking about what is happening when there is a current in a circuit. That’s when I get them to do the role play. It helps students to understand some of the science ideas about electric circuits. Basically, I want students to understand that in a complete circuit, there is a flow of charged particles and a transfer of energy from the battery to an energy user such as a light globe. Students often confuse current with energy, and the role play helps them to discriminate between the two. It helps develop other ideas as well. For example, when I think students have got the idea that the ‘charged particles’ in the role play each get the same number of jellybeans, which they then give to the ‘light globe’, I go to the board and summarise what is happening.” She scribbles on some paper:

‘Energy’ supplied by ‘battery’ per ‘charged particle’ = 2 ^Jellybeans/_{’Charged particle’} = 2 ^J/_C

‘Energy’ transferred to ^{‘light globe’}/_{used up per ‘charged particle’} = 2 ^Jellybeans/_{’Charged particle’} = 2 ^J/_C

“I think I can see where you are going with that,” interposed Mr Hall. “You’re wanting to stress that energy is conserved and also get students used to the units of ^J/_C because they are the same ones that scientists use. I guess at some point you’ll tell the class that scientists use J to represent the number of joules of energy and C to representing the number of coulombs of charge, and that 1 joule/coulomb is the same as one volt!”

Ms Smith nodded. “You caught onto that very quickly! And the students do, too – or at least the idea that each charged particle in the role play should get the same number of jellybeans and give these up to the light globe. I test this by asking them to predict what would happen if the ‘battery’ gave each charged particle four jellybeans. Usually they quickly decide that each ‘charged particle’ would give all four jellybeans to the ‘light globe’ although there is some discussion before everyone realises that the ‘light globe’ has to show he/she has been given more energy by, for example, waving his/her arms more rapidly.

“When I think they have got the idea that energy is conserved, we go back to using a two jelly bean battery in the circuit; I tell the class that if this was a real circuit, the light globe would actually get a tiny bit less than two jelly beans from each charged particle, and ask why. This leads to a consideration of energy ‘lost’ in the wires and paves the way for some discussion of resistance in later lessons.

“One of the other things that I do,” Ms Smith continued, “is to wait for a moment when the ‘charged particles’ are bunched up a bit or unevenly spread as they move around the circuit. Then I call out ‘stop’ and ask the class what the ‘charged particles’ could do to represent the current in a circuit more accurately. Usually they pick up fairly quickly that the ‘charged particles’ need to be uniformly spread as they move around the circuit.”

“Yes, but it’s fairly trivial – it’s because some of the modifications to the role play that we explore later involve two light globes in series. If the battery provided one jelly bean per charged particle, the jelly bean would have to be cut in two so half could be given to each light globe. This could provide an added complication that might distract students from thinking about how energy is shared in a circuit with two light globes in series, which is really tricky to understand. So I stick with a two jelly bean battery!”

“Well, that all seems fairly straightforward to me,” observed Mr Hall.

“Yes, it is in some ways,” replied Ms Smith, “but, of course, real circuits are more complex to understand than the role play suggests. And it’s important to help students understand this if their learning is to progress.

“Once the class is familiar with the role play and can see the way it links with the behaviour of a simple circuit, I then spend some time considering aspects of a simple circuit that the role play doesn’t explain. One of the things that I want the students to understand is that this role play, like all models, has its limitations, and that understanding the limitations of a model is an important part of understanding both the model and the thing that it is modelling! In other words, to understand both the role play and electric circuits, you have to understand the ways in which the role play is different to an electric circuit. And because of these limitations, which are ones that scientists also face with models they develop, we have to modify our model or seek a better one. I try to develop these ideas by considering what happens when a second light globe is introduced into the simple circuit we have talking about.”

Ms Smith continued, “So I ask the students how the role play needs to be modified to model what happens when in a circuit with two light globes in series. This is a really difficult question for many students. Some will want to give both jelly beans to the first light globe. We talk about what that would mean in a real circuit – one globe would glow and the other wouldn’t – which is contrary to what they observed during their experimental work when they set up two light globes in series. Eventually someone may correctly suggest that one jelly bean should be given to the first light globe and one to the second. This presents a problem for lots of students – how do real charged particles ‘know’ in advance of arriving at the second light globe that the second light globe is present in the circuit and that they should ‘give’ the first light globe only half of what they had given it when it was the only light globe in the circuit. It’s important to acknowledge this difficulty, for it is a problem that even applies to circuits with one light globe – why is all the energy provided by the battery given to the light globe? Before considering this issue, I talk about the ways that scientists have to modify their ideas when their models or explanations do not explain some aspect of phenomena. I close the lesson by telling the students that scientists use the idea of fields to explain what determines how much energy the light globes receive in an electric circuit: I tell them that it’s a bit like the changeable speed signs that we now have on our roads – the ones where the speed limit changes according to the time of day or traffic conditions. Just as the speed signs control the speed of traffic at different points on the road, the field controls how much energy the charged particles give to each light globe in the circuit. And just as the speed signs can be changed to suit changes in the traffic conditions or time of day, so too the field can change to accommodate changes in the circuit. I reassure them that I’ll be following up these ideas in later lessons to help them better understand the ideas.

“If you’re interested I can talk about what I do in those lessons some other time. But for now, how about we get a cup of coffee and then I’ll tell you about what I think are some negative aspects to using the role play.”

Some cons

Ms Smith sipped her coffee. “One of the difficulties with the role play is that it can reinforce students’ tendency to think of charged particles in anthropomorphic terms – in other words, the charged particles are like people and what they do is a function of their own decision-making processes. Even though we use the idea of a field to explain the behaviour of charged particles, this view that charged particles have to decide how much energy to ‘give up’ tends to linger.

“And of course, the idea that charged particles carry energy to the light globe is also a bit misleading. Really a more scientific one understands that the energy transfer to the light globe is a consequence of the battery pushing the charged particles through the circuit. It doesn’t worry me that students don’t have this view yet, but I’ve found that one consequence of the idea that charged particles carry energy to the light globe is that some students, once they’ve been introduced to the idea of potential difference, then think that current causes potential difference.

“So there are some drawbacks to using the role play. It’s vital that students’ understand how the role play is both similar and dissimilar to a real circuit and are exposed to a number of other analogies, metaphors and models to explain circuits. And I think it’s important to revisit each of these from time to time. It’s especially important after some new science ideas have been developed to see what, if any, are the links between the new concepts and each analogy, metaphor and model that has been discussed. For example, after my students have encountered some ideas about power, say, I go back to the role play and get them to think about what aspects, if any, of the role play might link with power. And I get them to do this for other analogies, metaphors and models we have used.”

“Gee,” exclaimed Mr Hall, “I’ve never thought about a role play as problematic before! I’ve just tended to think a role play is good to do occasionally because it’s a bit different and it’s easy. You’ve helped me realise that simplifying things, as in the Jelly Bean Role Play, can actually impede understanding. I now see that I’ve got to acknowledge the complexity of science ideas about electric circuits to my students if I want to help develop their understanding. I’m starting to realise there’ll need to be lots of class discussion in this unit and that the role play could be a springboard for generating some of this discussion. I’ll try it and let you know how I go ...”