Practical takeaway
Voltage provides the electrical push, current is the flow of electrons in a circuit, resistance opposes current, and power tells you how fast electrical energy is being used.
T5A · Current and voltage
Current, Voltage, Conductors, AC & DC
The practical electrical vocabulary underneath almost everything else in radio.
Technician exam focus
Know the names and units, why metals conduct, what makes a good insulator, how AC differs from DC, and what frequency means.
1. Current and voltage
Current is the flow of electrons in an electric circuit and is measured in amperes (amps, A). Voltage is electrical potential difference — the electrical “push” that causes electron flow — and is measured in volts (V). You may also see voltage described as electromotive force (EMF).
CurrentFlow of electronsamperes (A)
VoltagePotential difference / electrical pushvolts (V)
PowerRate electrical energy is usedwatts (W)
FrequencyComplete AC cycles each secondhertz (Hz)
2. Conductors and insulators
Metals are generally good conductors because they have many free electrons that can move through the material. Copper is a familiar example. An insulator does not allow electrons to move easily; glass is the Technician-pool example to remember.
Exam shortcut: “many free electrons” is why metals conduct well. Glass is the good insulator among the current T5A choices.
3. AC, DC and frequency
Direct current (DC) keeps the same polarity and flows in one direction. Alternating current (AC) reverses direction, alternating between positive and negative directions. Frequency tells you how many complete AC cycles occur each second; its unit is the hertz.
Resistance opposes current flow whether the current is DC, AC, or RF. At radio frequencies there can also be frequency-dependent opposition called impedance, which T5C introduces.
T5A checklist
- Current → amperes.
- Power → watts.
- Flow of electrons → current.
- Cycles per second → frequency; unit → hertz.
- A voltage difference causes electron flow.
- Metals conduct well because they have many free electrons.
- Glass is a good electrical insulator.
- AC alternates between positive and negative directions.
- Power is the rate at which electrical energy is used.
- Resistance opposes DC, AC and RF current.