A circuit whose output is directly proportional to its input, over a given range of values. The performance of such a circuit is linear. This course is a first introduction to electrical systems. It includes the analysis of circuits including resistors, capacitors, and inductors with DC and AC sources in the time domain and in the frequency domain. Laboratory demonstrations are given to reinforce the concepts learned from the lectures and homework. The course is targeted at people with a scientific or technical background who are not electrical or computer engineers. The coverage is not as deep as a circuits course aimed at electrical engineers. There are a number of physical applications demonstrated in this course that serve to motivate this topic to a wider audience.