Question T5C12
From subelement T5 - T5C
What is impedance?
Why is this correct?
Impedance is the total opposition to alternating current (AC) flow in a circuit, measured in ohms. While resistance opposes all types of current flow (DC, AC, and RF), impedance specifically describes AC opposition and combines both resistance and reactance effects. Reactance comes from capacitors and inductors, which affect AC differently at different frequencies. Choice B is wrong because impedance isn't the inverse of resistance. Choice C confuses impedance with Q factor, which measures circuit selectivity. Choice D incorrectly describes power handling capability.
Memory tip
Remember the key pattern: resistance applies to all current types, but impedance is AC-specific. When you see 'impedance' in questions, think 'AC circuits with frequency-dependent effects.' This distinction helps identify impedance-related answers versus simple resistance questions.
Learn more
In practical amateur radio operation, impedance matching is critical for efficient power transfer between your transmitter and antenna system. A 50-ohm coaxial cable connects your radio to a 50-ohm antenna system to minimize standing wave ratio (SWR). Impedance mismatch causes signal reflections, reducing transmission efficiency and potentially damaging your equipment. Understanding impedance helps you design proper RF circuits and troubleshoot antenna system problems.
Think about it
Why do you think impedance becomes more complex than simple resistance when dealing with AC signals, especially at radio frequencies?