18.4 Data from Tutorials
When students were requested to preview the pattern collected on a screen by light
passing through two slits, respectively of width 0.5–1 cm and less than 1 mm
(Tutorial 1—question T1A), they answered according to the four categories summarized in Table 18.1.
The majority of the 168 students of the sample expected some features typical of a
diffraction phenomenon, where the “expansion” of light after the slit is the aspect
more quoted (65%). This is a consequence of the fact that these students faced the
basis of diffraction and interference in school before the CLOE lab. Some students
(21%) expected an “enlargement” of the light pattern in a direction parallel to that of
the slit, underlying a particle-like conception of wave propagation of light. A great
group (49%) previewed that the narrower the slit is, the narrower the illuminated area
on the screen will be, according to a geometric rectilinear path model.
Concerning the light intensity versus position distributions expected, the
Table 18.2 resumes the main categories. In the DA category was putted all the
representation catching the main features of the experimental graph. The second
category (DB—equal peaks graph) differs from first because the central maximum is
of the almost the same intensity of the first order maxima (changes from DB to DA
occurred frequently in the representation of the observed graphs). The presence of
maxima and minima characterize also the subcategory DB
0 exemplified in Fig. 18.1
and showing discontinuity in the intensity distribution. The other three categories of
Table 18.1 (DC, DD and DE) differ for the mathematical function used (bell or
parabolic shape, inverse power shape, linear shape) to represent in any cases the
envelope of the maxima intensity.
After observing the diffraction figure produced by a 0.12 mm vertical slit, the
majority of students (72%) stressed the presence of an enlargement of the pattern,
and added in half of cases that the distribution is “perpendicular” to the slit direction.
Just 17% of the sample evidenced the presence of points/lines. The “enlargement” of
the light pattern is quoted more frequently, because it can be included in a straightline model of light. Highlighting maxima/minima requires almost activating a
change in the standard point of view of geometrical optics. The model that students
had in mind affects strongly the recognition of the main features of the phenomenon
observed (Karmiloff-Smith 1988; Chinn and Brewer 2001).
Figure 18.2 shows the distributions of the representation categories drawn by
students before performing the experimental acquisition with sensor (prevision) and
after observing the experimental graph on the screen (observed). The prevision
Table 18.1 Categories of previsions on the behaviour of light passing through a slit
Cat
Large slit (0.5–1 cm)
Tin slit (less than 1 mm)
%
A
Light more large
Light less large
49
B
Light remains the same
Light is expanded
44
C
Light remains the same
Light is expanded vertically (same direction of the slit)
21
D
Light remains the same
More lines inside
7
228
A. Stefanel
When students were requested to preview the pattern collected on a screen by light
passing through two slits, respectively of width 0.5–1 cm and less than 1 mm
(Tutorial 1—question T1A), they answered according to the four categories summarized in Table 18.1.
The majority of the 168 students of the sample expected some features typical of a
diffraction phenomenon, where the “expansion” of light after the slit is the aspect
more quoted (65%). This is a consequence of the fact that these students faced the
basis of diffraction and interference in school before the CLOE lab. Some students
(21%) expected an “enlargement” of the light pattern in a direction parallel to that of
the slit, underlying a particle-like conception of wave propagation of light. A great
group (49%) previewed that the narrower the slit is, the narrower the illuminated area
on the screen will be, according to a geometric rectilinear path model.
Concerning the light intensity versus position distributions expected, the
Table 18.2 resumes the main categories. In the DA category was putted all the
representation catching the main features of the experimental graph. The second
category (DB—equal peaks graph) differs from first because the central maximum is
of the almost the same intensity of the first order maxima (changes from DB to DA
occurred frequently in the representation of the observed graphs). The presence of
maxima and minima characterize also the subcategory DB
0 exemplified in Fig. 18.1
and showing discontinuity in the intensity distribution. The other three categories of
Table 18.1 (DC, DD and DE) differ for the mathematical function used (bell or
parabolic shape, inverse power shape, linear shape) to represent in any cases the
envelope of the maxima intensity.
After observing the diffraction figure produced by a 0.12 mm vertical slit, the
majority of students (72%) stressed the presence of an enlargement of the pattern,
and added in half of cases that the distribution is “perpendicular” to the slit direction.
Just 17% of the sample evidenced the presence of points/lines. The “enlargement” of
the light pattern is quoted more frequently, because it can be included in a straightline model of light. Highlighting maxima/minima requires almost activating a
change in the standard point of view of geometrical optics. The model that students
had in mind affects strongly the recognition of the main features of the phenomenon
observed (Karmiloff-Smith 1988; Chinn and Brewer 2001).
Figure 18.2 shows the distributions of the representation categories drawn by
students before performing the experimental acquisition with sensor (prevision) and
after observing the experimental graph on the screen (observed). The prevision
Table 18.1 Categories of previsions on the behaviour of light passing through a slit
Cat
Large slit (0.5–1 cm)
Tin slit (less than 1 mm)
%
A
Light more large
Light less large
49
B
Light remains the same
Light is expanded
44
C
Light remains the same
Light is expanded vertically (same direction of the slit)
21
D
Light remains the same
More lines inside
7
228
A. Stefanel