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Units of Measure
Symbols
Voltage, Current, Resistance and Power
Voltage is the measure of electrical pressure or potential difference between 2 points on a circuit
Current is a measure of the electron flow in a circuit
Resistance is the opposition to electron flow in a circuit.
Power is a measure of the energy consumed by a circuit.
| Measurement | Units | Abbreviation |
| —– | —– | — |
| Voltage | Volts | V |
| Current | Amps | A or I |
| Resistance | Ohms | R or Ω |
| Power | Watts | W or P |
| Frequency | Hertz | Hz |
| Wavelength | Metres | M or λ |
Current
Current is the flow of electrons in a circuit. There are two types of current, Alternating Current and Direct Current.
Direct Current
Direct Current is usually shortened to DC. In a DC circuit the flow of electrons is always from the negative power sounce towards the positive terminal of the power source.
Alternating Current
Alternating Current is usually shortened to AC. In an AC circuit the flow of electrons alternates at some frequency. For example, current flow in our mains AC power alternates at 50Hz or 50 cycles per second.
Basic Circuit Symbols
One of the requirements of the Foundation qualification is the recognition of some basic component and radio circuit symbols. These are universal and will often appear within radio manuals. Exam candidates should memorise these items.
| Name | Diagram |
|---|---|
| Cell |  |
| Battery |  |
| Fuse |  |
| Lamp |  |
| Resistor |  |
| Switch |  |
| Antenna |  |
| Earth |  |
| Microphone |  |
| Loudspeaker |  |
Next Module: Transmitters & Receivers
References & Further Reading
Syllabus
Syllabus items covered by this module.
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