Clive W. Humphris

**AC THEORY: AC Ohm's Law. **

Ohm's Law can also be applied to AC circuits. However, alternating currents and voltages are continually changing. At the beginning of the cycle the voltage and current are zero, building to peak positive values at 90°, before declining back to zero, and then repeated in a negative direction.

It is therefore only possible to calculate instantaneous values of V or I throughout the cycle. Peak or RMS values are normally used.

The AC resistance of capacitors and inductors is called 'reactance' (measured in Ohms). As the frequency is increased, capacitive reactance decreases, whereas inductive reactance increases.

Once the reactance is calculated for C or L at the applied frequency, the value can be inserted in the formula as for resistance. Where there is a combination of resistance and reactance the calculation refers to 'impedance', symbol Z.

- Table of Contents
- Interactive eTextbooks
- Basic Electronics
- Conductor And Insulator
- Resistor Value Test
- Simple Dc Circuits
- Types Of Switching
- Variable Voltages
- Ohm's Law
- DC Voltage
- DC Current
- Series and Parallel Resistors
- AC Measurement
- AC Voltage and Current
- AC Theory
- RCL Series
- RCL Parallel
- Capacitance
- Capacitors
- Inductance
- Inductors
- Impedance
- Radio and Communication
- Tuned Circuits
- Attenuators
- Passive Filters
- Active Filters
- Oscillators
- Circuit Theorems
- Complex Numbers
- DC Power
- AC Power
- Silicon Controlled Rectifier
- Power Supply
- Voltage Regulation
- Electro-Magnetism
- Electrical Machines
- Transformers
- Three Phase Systems
- Energy Transfer and Cost
- Atomic Structures
- Diode Theory
- Diode Applications
- Transistor Theory
- Bipolar Transistors
- Transistor Configurations
- Active Transistor Circuits
- Field Effect Transistors
- Basic Operational Amplifier
- Op-Amp Theory
- Op-Amp Applications
- Sum and Difference Amplifiers
- Analogue Multi-Meter
- Component Testing