Series and Parallel

A series circuit is a circuit where the current only goes through one path. This series circuit is used to simulate an AND gate. The output of an AND gate is true when all of the inputs are also true.

Because the switches and LEDs are all in a line, when one switch is not pushed it breaks the flow of electricity for the entire circuit. It is only when both switches are pushed that electricity can flow through and light up the LEDs. 

A parallel circuit is a circuit where the current branches off into separate paths. This parallel circuit is used to simulate an OR gate. The output of an OR gate is true when any of its inputs are true.

Becuase each pair of switch and LED has its own complete path for the electricity to flow, the circuit needs only one of the switches to be activated for it to be complete. This allows for one LED to be on separate from the other depending on which switch is pressed.