Circuit

A circuit refers to a system where various electrical and electronic components are connected and interact with each other in response to supplied voltage and current. It is also called a 'circuit' when a path is created using conductors and various components that allows electric charge to travel in a loop and return to its original position. In thermodynamics terms, it's similar to a system in an ideal gas.

When introducing the concept of circuits to students, it's often compared to water flow. This makes it convenient to teach the concepts of voltage (water pressure) and current (flow rate). However, electrical circuits differ significantly from water channels, so these differences must be clearly understood:

• Water channels allow water to flow even without one end connected to the other, but electrical circuits require a closed loop for electricity to flow.

• Electric current doesn't flow through the circuit like water molecules. It's more like sound waves or seismic waves that transmit vibrations while remaining in place.

For more details, see circuit theory documentation.

In the mid-to-late 20th century, circuit building was a popular hobby among students. At that time, before integrated circuits were developed, circuits referred to discrete circuits made by soldering various components to boards. Students would purchase universal PCBs and components from electronics or science shops to build radios, sensors, etc. as a leisure activity. Magazines like "Electronic Science" and "Radio and Models," which introduced circuit diagrams for various devices, were widely read and popular among students.

However, as integrated circuits advanced and various microchips with complete circuit functions emerged—which couldn't be DIY-built by ordinary people—circuit building gradually disappeared as a hobby. In countries like the US and UK, circuit-building hobbies evolved into microcomputer construction like the Altair and Apple 1, but in Korea, electronics as a hobby ended in the 20th century.