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

New Trends in Physics Teaching IV
‘My idea is that the moment you see something, if it’s in the dark, it must be sending out light. . . . If I see something
in complete darkness, and I see that thing, like that [he points to the lighted incense stick] or a lamp, I
think it must be sending out light. If I see it a hundred metres away, it must be sending out light to a hundred
metres. If I see it at a hundred and fifty metres, it’s sending out light to a hundred and fifty metres . . . . . . . . at
least provided that it’s in complete darkness. Because if I see a cupboard or my coat because there’s light, I
see it. But if in complete darkness I see something . . . and I can’t see anything else, well I think it must be sending
out light. Because I can see it’ [E19,12 years, 5 months].
E 19 clearly distinguishes here between the case of glowing objects and that of ordinary objects.
Rare as it is for it to be recognized that light is received by the eye in the case of an object such
as the incense stick, it is even rarer in the case of ordinary objects. One child alone gave the same
answer concerning the cardboard box as he had given concerning the glowing incense stick, thus
giving proof of an interpretation that was satisfactory from the physicist’s point of view:
‘. . . if I see the object . . . it must be because it gives me a bit of light. So . . . I can see it. . . .It [the light] gets to
my eye . . . and then my eye it . . . it records. And it makes it possible, er . . . in my brain to form an image of
the object’ [E18, 14 years].
object
brain
eye
Figure 6.
Another viewpoint
Child E6, who was one of those who considered that the eye received light in the case of the
glowing stick, said to us in respect of the cardboard box, contrasting it with the previous case:
‘Here my eyes can go right up to the box. . . . It’s my sight. . . . If it [the box] was fifteen kilometres away, I
couldn’t see it, because . . . my sight isn’t strong enough. . . . Because a box doesn’t move, it hasn’t any energy.
A lamp, for instance, which moves, the light gets there. . . . The box, is something that isn’t alive.’
What we have here is an interpretation of the phenomenon of vision in which the eye is thought
not to receive light but, on the contrary, to be an active agent. Likewise, E 12 [ 13 years, 8 months]
said to us:
‘It’s pretty much like the light, because it comes out. . . . The eye sees like this . . . it comes out like this [he
draws lines going forwards or upwards from the eye according to the direction in which the eye is looking]. . . .
The eyes haven’t got any light of their own, so they have to have a light that lights up when you want to see.’
In everyday language, which serves as a source or a reflection of commonly held views, the
same idea is expressed. The eye is assigned an active role, whereas the object ‘looked at’ has but
a passive role: the eyes examine, search out, scrutinize, and so on. In romantic literature eyes
flash, looks can kill. . . . And it is true that when one looks at an object, one has the impression
of being more an active subject than a passive receiver. Any comprehensive theory of vision
includes physical, physiological and psychological aspects. This sense of an active subject,
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