In this paper, we present activities that help students deepen their understanding of basic electrostatics using an electroscope in combination with the photoelectric effect. The students investigate the behaviour of an isolated electroscope when the metal housing of the electroscope is charged. The activities follow the framework of the Investigative Science Learning Environment (ISLE) approach to learning and teaching. ISLE helps students learn fundamental physics concepts by engaging them in processes that mirror those used by physicists when they develop new knowledge and use it for practical applications.