Switches might seem simple, but they are absolutely crucial to designing useful electrical systems and devices. Typically, a switch is a component that can be manipulated either to close or open a circuit. For example, flipping on a light switch closes the circuit between the power source and the bulb, allowing current to flow freely and illuminate the room. Circuit breakers, shown above, are another kind of switch -- they're designed to automatically open a circuit that is in danger of overload.