Passive components
Resistors turn electrical energy into heat and set current for a given voltage. Capacitors store energy in an electric field between two plates. Inductors store energy in the magnetic field of a coil and resist changes in current.
Resistor values are printed as colored bands; the resistor color code calculator decodes four- and five-band markings.
| Component | Defining relation | Energy stored | Series | Parallel |
|---|---|---|---|---|
| Resistor (R, Ω) | V = I·R | none (dissipates P = I²R) | R = R₁ + R₂ + … | 1/R = 1/R₁ + 1/R₂ + … |
| Capacitor (C, F) | Q = C·V; I = C·dV/dt | E = ½CV² | 1/C = 1/C₁ + 1/C₂ + … | C = C₁ + C₂ + … |
| Inductor (L, H) | V = L·dI/dt | E = ½LI² | L = L₁ + L₂ + … | 1/L = 1/L₁ + 1/L₂ + … |
Sources: OpenStax: University Physics Volume 2, 10.2 Resistors in Series and Parallel; OpenStax: University Physics Volume 2, 8.1 Capacitors and Capacitance; OpenStax: University Physics Volume 2, 8.2 Capacitors in Series and in Parallel; OpenStax: University Physics Volume 2, 14.2 Self-Inductance and Inductors
Worked combinations
Series resistances add, so the total is always larger than the largest part. Parallel resistances combine by reciprocals, so the total is always smaller than the smallest part. Capacitors follow the opposite pattern, and inductors (without mutual coupling) follow the resistor pattern. For two parts in parallel, R = R₁R₂ / (R₁ + R₂).
| Parts | Series total | Parallel total |
|---|---|---|
| Resistors 100 Ω, 220 Ω, 470 Ω | 790 Ω | 59.98 Ω |
| Resistors 1 kΩ, 1 kΩ | 2,000 Ω | 500 Ω |
| Capacitors 1 µF, 2.2 µF, 4.7 µF | 0.6 µF | 7.9 µF |
| Inductors 10 mH, 10 mH | 20 mH | 5 mH |
Sources: OpenStax: University Physics Volume 2, 10.2 Resistors in Series and Parallel; OpenStax: University Physics Volume 2, 8.2 Capacitors in Series and in Parallel
Active and switching components
A diode lets current flow from anode to cathode and blocks it in reverse; a silicon diode drops roughly 0.6 to 0.7 V when conducting. A light-emitting diode (LED) emits light when forward-biased, and a Zener diode is designed to conduct in reverse at a specified breakdown voltage for regulation.
A transistor uses a small signal to control a larger current. In a bipolar junction transistor (BJT), collector current is approximately the base current times the current gain: I_C ≈ β·I_B. In a MOSFET, the gate voltage controls the channel with almost no steady gate current, which makes MOSFETs the usual choice for power switching and digital logic.
A DIP switch is a set of miniature SPST switches in a dual in-line package, used to set configuration bits on a circuit board. With n switches there are 2ⁿ possible settings.
| Switches | Settings |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 8 |
| 4 | 16 |
| 6 | 64 |
| 8 | 256 |
| 10 | 1,024 |
| 12 | 4,096 |