Final answer:
Switches are used to start, stop, or change the direction of the current in a circuit.
Step-by-step explanation:
The devices used to start, stop, or change the direction of the current in a circuit are switches. Switches are similar to valves in a water circuit. When the switch is open, no current passes through the circuit, but when it is closed, the current flows through it. Switches are represented by standardized symbols in circuit schematics and can be found in various electrical appliances.