As a consequence of international educational studies like TIMSS and PISA, quality of instruction has become a central topic in the discussion between educators, researchers, and policymakers. Teacher competencies are preconditions for instructional quality. This study focuses on the impact of perceived teacher competencies on student well-being and anxiety in physics instruction. Student emotions are one important aspect of the educational process and supposed preconditions of sustainable learning processes. In the study, we combine both qualitative and quantitative methods using questionnaires and semi-structured interviews. In total, 431 students from 16 classes participated in this study: 24 students and eight physics teachers were participants of the qualitative study. Each teacher taught two classes, and therefore a comparison of the ratings of each teacher by students of two different classes was possible. The results of our study confirm the assumption that perceived teacher competencies have an impact on student emotions. Analysis of the qualitative data supports the quantitative results and demonstrates the importance of teacher competencies for student emotions. By comparing qualitative and quantitative results, we demonstrate the advantages and disadvantages of each method. Consequently, we suggest a combination of qualitative and quantitative methods. (Contains 7 tables and 2 figures.)