Purba, Frikson Jony. “INFLUENCE MODEL PROBLEM BASED LEARNING (PBL) UNDERSTANDING THE CONCEPT OF BEGINNING OF SCIENCE PROCESS SKILL (KPS) SENIOR HIGH SCHOOL STUDENT”. Jurnal Pendidikan Fisika, vol. 4, no. 2, Dec. 2015, pp. 8-13, doi:10.22611/jpf.v4i2.3191.