Capacitors and inductors are introduced, along with their equivalent circuit laws. Switched RC circuits are thoroughly analyzed. The response of an RC circuit to a sinusoidal drive voltage is analyzed and leads to a discussion of high- and low-pass filters, phase shifters, integrators, and differentiators. The use of complex numbers in circuit analysis is introduced and applied to sinusoidally driven series RC, LR, and LRC circuits as well as the switched LRC circuit. Fourier analysis and its meaning are presented. The operation of transformers is introduced.

Chapter 3.8 introduces the basic principles of electricity, from current and flow in Ohm’s law, to resistance and impedance within electrical circuits. We discuss the danger of electricity within medical equipment, of the different types of electrical shock and measures in place to reduce the risk of electrical injury. We cover classification of electrical equipment according to safety measures.

Electrical forces, electric fields, and electric field lines are considered and can be understood as arising from positive and negative electrical charges. Of most importance on an everyday scale will be the charge imbalance between positive and negative, known as the net charge. A net charge can be stored using two electrical conductors that are near to each other but separated by an insulating region. A device designed to do this is a capacitor. Resistors are devices that act like friction in an electric circuit and are one type of impedance found in electronics. Capacitors and resistors are characterized by capacitance, C, and resistance, R, respectively. A resistor connected to a capacitor will have behavior characterized by a time constant, RC—the product of the resistance and capacitance. It is one example of many systems that have a characteristic time scale. Some basic electronic schematic symbols are presented and used to demonstrate the exponential behavior of RC circuits. Similar circuits can be used to filter electrical signals—for example, to block low- or high-frequency signals and thus change the overtone content.