According to Alice (17 year old A level student) A balloon could be attached to a wall by charging, so that there was a ‘glue effect’ with an attraction between areas of positive and negative charge. A negatively charged balloon could be attached to a neutral wall because it was relatively positive,
Alice proposed that “because you’ve got opposite charges, you’ve got the say negatively charged balloon, and then your positively charged wall”. Although the wall “hasn’t had anything done to it as such”, Alice suggested that “maybe in comparison to your very negatively charged balloon, it’s still likely to attract.” Alice agreed that she was suggesting that “it’s relative”, that because the neutral object is positive by comparison with the negative object, they’re effectively both charged.

Amy (Y10) suggested that a circuit was “a thing containing wires and components which electricity can pass through…it has to contain a battery as well”. She thought that electricity could pass through “most things”.

For Amy “resistance is anything which kind of provides a barrier that, which the current has to pass through, slowing down the current in a circuit”, and she thought about this in terms of the analogy with water in pipes: “we’ve been taught the water tank and pipe running round it… just imagine the water  like flowing through a pipe, and obviously like, if the pipe becomes smaller at one point, erm, the water flow has to slow down, and that’s meant to represent the resistance of something”. So for Amy charge flow was impeded by physical barriers effectively blocking its way. She made the logical association with the density of a material, on the basis that a material with densely packed particles would have limited space for the charge to flow:

So electricity would “not very easily” pass through a wooden bench “because wood is quite a dense material and the particles in it are quite closely bonded”.

In air, however, the particles were “not as dense as a solid”. When asked if that meant that electricity can pass through air quite easily, Amy replied: “yeah, I think so”.

Jim, a Y7 student, had been studying burning in science. He had been using Bunsene burners, and had been taught about the different flames (i.e. the safety flame, and the ‘roaring’ blue flame used for heating), and the use of the vale at the base of the burner to select the frame. Not yet appreciating the nature of burning, he was not aware that the soot obtained when interrupting the safety flame was due to incomplete combustion. Rather he had developed his own interpretation of why using the burner with the hole closed off led to a dirty flame:

KST: What is burning, then?

Jim: It usually involves a flame.  Erm which can either be yellow, orangey-yellow, or …like a, bluey colour, bluey-purple.

KST: Oh, so is that significant, the colour of the flame, does that mean something?

Jim: Well, the yellow one has a lot of …if you touch it with glass or something,  …will go black, but if you use the blue flame, it won’t, so if you are heating something, you should use the blue flame.

KST: Why do you think it goes black, if you use the organey-yellow flame?

Jim: Because with the Bunsen burners, if you are twisting the knob, open, the dirt gets out, and you get the nice clear blue flame, but to get the orange flame, you have to have it closed, don’t you, and then that doesn’t let the dirt out, so it doesn’t kind of, when it gets out of the top it doesn’t have time.

KST: So what happens if the hole is open?

Jim: You get, a blue flame.

KST: Right, and what happens if the hole is closed?

Jim: Get a yellow flame.

KST: And why does the hole make a difference?

Jim: I don’t know, it probably lets the dirt out, or the air get into it or something.

KST: So what dirt is this, that might be let out, do you think. Dirt from where?

Jim: Maybe the excess gas particles that have already been burnt or something. Don’t know.

Presumably no one had told Jim that the hole was to let dirt out of the Bunsen so it did not get into the flame. However the hole was presumably letting something in or out (he later suggests, the hole might let air in -  perhaps something the teacher had told the class but which had not been readily recalled?) and there was dirt in the flame when it was closed, which was not there when it was open. Jim interpreted his observations interms of prior knowledge (of what holes do, and of dirt) to construct an explanatory scheme that made some sense of the effect of closing or opening the air hole.