| Octal numeration | Octal and hexadecimal numeration |
| octave | AC Waveforms |
| oersted (unit) | Magnetic units of measurement |
| offset null | Offset Voltage |
| offset voltage | Offset Voltage |
| ohm | Ohmmeter Usage |
| Ohm (unit) | How voltage, current, and resistance relate |
| Ohm's law | Correct use of Ohm's Law |
| | DC circuit equations and laws |
| | Magnetic units of measurement |
| | Series R, L, and C |
| | Series resistor-capacitor circuits |
| | Series resistor-inductor circuits |
| | Some examples with AC circuits |
| | Simple AC circuit calculations |
| | Ohm's Law |
| | Ohm's Law |
| | Applications of Ohm's Law |
| Ohm's Law, AC | AC Circuit Equations |
| Ohm's Law, AC version | Phase shift |
| Ohm's Law, correct context | Simple series circuits |
| | Simple parallel circuits |
| ohm's law, fo | Magnetic units of measurement |
| Ohm's Law, qualitative | Component failure analysis |
| Ohm's Law, water analogy | An analogy for Ohm's Law |
| Ohm, unit | Susceptance and Admittance |
| Ohmic region, JFET | Active-mode operation |
| Ohmmeter | Ohmmeter design |
| ohmmeter usage | Ohmmeter Usage |
| Ohms per volt | Voltmeter impact on measured circuit |
| One's complement | Negative binary numbers |
| one-shot | Time-delay relays |
| | Contact "bounce" |
| One-shot, nonretriggerable | Monostable multivibrators |
| One-shot, retriggerable | Monostable multivibrators |
| Op-amp | The "operational" amplifier |
| | Offset Voltage |
| | Bias Current |
| | Drift |
| | Feedback |
| | Differential Amplifier |
| | Simple Op-Amp |
| Open circuit | Resistance |
| Operational amplifier | The "operational" amplifier |
| | Feedback |
| | Introduction |
| | Multi-Stage Amplifier |
| | Differential Amplifier |
| | Simple Op-Amp |
| operational amplifier, programmable | Simple Op-Amp |
| Opposite | Trigonometry Reference |
| Optical fiber | Optical data communication |
| optical switch | Switch types |
| OR | Gate universality |
| OR gate | OR gate |
| OR gate, TTL | TTL NOR and OR gates |
| orbital | Angular Momentum Quantum Number |
| Oscillation | An electric pendulum |
| Oscillator | Applications of resonance |
| | Positive feedback |
| | Feedback |
| | Hysteretic Oscillator |
| Oscillator, relaxation | Gas discharge tubes |
| Oscillator, voltage-controlled | Microwave tubes |
| oscilloscope | What is a meter? |
| | AC Waveforms |
| | Frequency and Phase Measurement |
| | PC Oscilloscope |
| Oscilloscope coupling | Signal coupling |
| | Half-wave rectifier |
| Over-unity machine | Superconductivity |
| overall view | Frequencies of Electromagnetic Oscillation |
| Overcurrent protection | Safe practices |
| Overflow | Overflow |
| Overload heater | Contactors |
| overrange | Voltmeter usage |
| oversampling | Delta-Sigma ADC |
| Overtone | Standing waves and resonance |
| | Introduction |
| | Power quality measurement |
| overview | Frequencies of Electromagnetic Oscillation |
