Lubis, Annisyah, et al. “THE DEVELOPMENT OF PROBLEM BASED LEARNING (PBL) MODELS BASED ON BATAK CULTURE TO INCREASE SKILL STUDY RESOLUTION”. Jurnal Pendidikan Fisika, vol. 7, no. 1, June 2018, pp. 47-54, doi:10.22611/jpf.v7i1.8160.