If five identical electric fans rated at 120 volts DC are connected in series on a 600 volt circuit and one fan develops an open circuit, what will happen?

When fans are connected in series, the same current flows through each fan. Since the fans are rated for 120 volts, connecting them in series means that the total voltage requirement for all five fans is 600 volts (120 volts per fan multiplied by 5 fans).

If one fan develops an open circuit, it breaks the series circuit. In a series configuration, if there is an open circuit at any point, the current flow is interrupted entirely. Consequently, no current can pass through any of the fans, leading to all of them stopping. Therefore, with one fan open, none of the fans will operate.

This situation describes a fundamental property of series circuits where the failure of one component results in the failure of the entire system. Hence, none of the fans will run if one develops an open circuit.