Plain-language answer: Physical length is measured distance; electrical length is phase length at a frequency and depends on conductor, insulation, loading, geometry, and surroundings.
Why it matters in the antenna
A short loaded whip can be electrically resonant without behaving like a full-size radiator in efficiency or current distribution.
What to verify
Record physical dimensions and frequency, then measure or model the complete installed structure.
The common mistake
Calling an antenna full size because loading makes it resonant.
Operating boundary
Use the exact documented component, geometry, frequency, power, duty cycle, clearances, and feed/return system. Begin tests at low power and stop for heating, arcing, damaged insulation, or unstable supports.
