University students’ ideas about the role of the aperture and laser beam dimensions in formation of diffraction patterns

Abstract

Successful application of the Huygens–Fresnel principle often requires reasoning about the interplay of aperture and light beam dimensions for purposes of identifying the unobstructed part of the light beam which is the source of secondary waves. Therefore we decided to identify university students’ ideas about the role of this interplay in the formation of diffraction patterns. We conducted a survey research with 191 first-year students from the Faculty of Chemical Engineering and Technology at the University of Zagreb, Croatia. They were administered six constructed-response questions in which aperture or laser beam dimensions were varied and students were expected to verbally and pictorially describe how these changes would affect the diffraction pattern. It has been shown that 63% of students think that a change in the length of the vertical slit necessarily results in a change of the diffraction pattern, even when the illuminated portion of the slit remains the same. In addition, it has been found that nearly 40% of students believe that in optical grating diffraction an increase of beam diameter leads to bigger diffraction fringes. A possible way to overcome some of these difficulties would be to insist on consistent application of the Huygens–Fresnel principle.

Learning about wave optics: the effects of combining external visualizations with extreme case reasoning

“…Students believed that the interference fringes would elongate in the vertical direction which reflects the idea that changes of the height of the slit lead to similar effects as changes of the width of the slit, although for the horizontal dimension of the slit diffraction effects are prominent which cannot be said for the vertical dimension. This finding is in line with the results of the study by Mešić, Vidak, Hasović, and D -ekić, who showed that students exhibit many difficulties in understanding the role of the vertical dimension of the slit [7].…”

“…Consequently, they often fail to correctly predict what would happen if we would rotate the slits by 90 • . This is probably related to a lack of basic understanding of the Huygens-Fresnel principle [7].…”

“…It seems that many students believe that after rotation of the slits diffraction, effects are not prominent anymore. This could be related to the fact that university students often lack a basic understanding of the Huygens-Fresnel principle [7].…”

“…Consequently, learning wave optics is very important for conceptual understanding of other areas of physics, e.g., solid-state physics and quantum mechanics [3,4]. However, many students struggle with developing a basic understanding of wave optics [5][6][7]. Earlier studies have shown that students often do not understand whether they should use geometric or wave optics to solve standard textbook problems related to light phenomena [4,8].…”

Development of the High School Wave Optics Test

“…Concretely, students find it very difficult to develop a functional model of the wave optics phenomena (Mešić et al, 2016). Thus, many students believe that the transmission of light through a single slit depends on the amplitude of the sinusoidal wave of light (Ambrose et al, 1999) or that a wider light beam contributes to a wider central maximum diffraction pattern (Mešić et al, 2019b). In addition, they think that diffraction happens as a result of a superposition of the two secondary waves that originate at the two edges of the slit (Ambrose et al, 1999).…”