The purpose of this study is to analyze the explanation of interference and diffraction presented in high school physics textbooks. The definitions and the principles of interference and diffraction, as well as examples of interference and diffraction, in 13 physics textbooks according to the 2015 revised curriculum were analyzed. The definitions of interference were similarly described for each textbooks, but inaccurate expressions were found in the section describing coherence and constructive/destructive interference as a phase. Regarding diffraction, the degree of explanation of Huygen’s principle differed among textbooks, and some textbooks used the concept of 'interference' in the process of explaining the principle of diffraction. Examples of interference and diffraction have been described in various examples, but the same phenomena have been explained by using different principles (interference, diffraction) depending on the textbook. Based on the results, we discuss the unnecessariness of the dichotomy of interference and diffraction, as well as the teaching method for interference and diffraction.

Keywords: Interference, Diffraction, Physics textbook, Huygens’ principle, Dichotomous thinking