New trends in physics teaching, v.4; The ... - unesdoc - Unesco

New Trends in Physics Teaching IV
already done so. We wanted to know how they interpreted this.
E17 (13 years): ‘. . . It makes it bigger. . . . So it ought to make the light bigger. And as the light heats up anyway.
. . . Because if you put it there, at the end of an hour, it’s going to bum. . . . But as the lens makes it
bigger. . . . . . . . there’s going to be lots of light, I think.’
E15 (13 years, 2 months): ‘It concentrates the light.’
I (interviewer): ‘Yes. Yes, you can make a drawing.’
E15: ‘As the light is more or less hot. ...’
I: ‘Yes. Here you are, do a drawing. Show me where the sun is, where you put the paper and the lens.’
E15: ‘Well, here for instance is the sun. [I: Yes.] The paper is there. [I: Yes.] It spreads out all around. It goes
like that and therefore it’s concentrated.’
Figure 4.
I: ‘Is there more light behind the lens than in front?’
E15: ‘No, but it’s more concentrated in one spot.’
Children of 13 and 14 are divided, in comparable numbers, between these two answers: ‘The
magnifying glass makes the light bigger’ or ‘The magnifying glass concentrates the light’. Among
the children who think that the magnifying glass makes the light ‘bigger’, some, like the first child
[E17], think that there is more light behind the magnifying glass; others think that there are ‘just
as many rays, but they’re . . . they’re stronger’ [E 10,14 years, 7 months] . Those children who have
the idea that the magnifying glass concentrates the light are not necessarily as close to the view
held by the physicist as is the child EIS. Thus E18 (14 years) produced the following drawing
(figure 5) to show how the magnifying glass concentrates the light. However, all consider that the
total amount of light passing through the magnifying glass is conserved, in contrast with those
children who think that the magnifying glass makes the light ‘bigger’, i.e. increases or intensifies it.
We encountered other cases where the idea that the quantity of light is conserved was not
expressed by the children. Thus, for some, light is subject to change with distance:
‘. . . At one point it stops because it’s too far. . . . At one point it can’t go on . . .you can’t see it any more. . . .
I think that it can’t go through air any more, or else it . . . it’s because it can’t go through the air any more, it’s
lost its . . . its density’ [E17, 13 years] .
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