After being awarded the 2001 Nobel Prize in Physics, Carl Wieman was struck by the effectiveness of a number of physics simulations that he used to explain his concepts to students and faculty. Combining over half of his Nobel Prize winnings with other funding sources, he founded Physics Education Technology (PhET) at the University of Colorado at Boulder in 2003. The site now has 115 active simulations in 65 different languages, totaling over 25 million downloads in 2011 alone. In this audio interview, Sheela Sethuraman speaks with Katherine Perkins, Director of PhET since 2008. They discuss what differentiates PhET from other physics simulations, and the range of students that have benefited from the program. As The Tech Awards 2011 Laureate and recipient of the Microsoft Education Award, PhET has continued to grow and adapt their simulations for a growing audience in recent years.