This study aimed to identify if complementing representations of concrete objects with representations of abstract objects improves students' conceptual understanding as they use a simulation to experiment in the domain of "Light and Color". Moreover, we investigated whether students' prior knowledge is a factor that must be considered in deciding when to use representations of abstract objects. A pre-post comparison study design was used, involving 69 participants assigned to two conditions. The first condition consisted of 36 students who had access to a simulation with representations of concrete objects, whereas the second condition consisted of 33 students who had access to a simulation with representations of both concrete and abstract objects. Both conditions used the same inquiry-oriented curriculum materials, consisting of three sections that included physical phenomena with increasingly complex underlying mechanisms, so that the third section's mechanisms were more complex in nature than those in the first two sections. Tests were administered to assess students' conceptual understanding before and after the presentation of the curricular material as a whole, as well as before and after each of its three sections. Results revealed that the presence of representations of abstract objects was helpful for the first two sections, but only for students with low prior knowledge. On the third, most complex section, also the students with higher prior knowledge profited from the presence of abstract objects. From these findings, we conjecture that for physical phenomena with a lower level of complexity, students with high prior knowledge are able to mentally construct the necessary abstract concepts on their own, whereas for higher levels of complexity they need an explicit representation of the abstract objects in the learning environment.