Sometimes you need to know which wire/node is positive polarity and which wire/node is negative polarity.The LED as a polarity indicator circuit is show in above diagram ... only these there are many ...

When the switch is tuned off, the circuit is open so the electrical energy stops flowing. Circuit symbols are really useful when designing ... A circuit diagram helps electrical engineers know ...

Their superconducting diode bridge, introduced in a paper published ... we decided to exploit them for applications. We thus explored useful circuits that could be made with such SDs." ...