Question T5A09
From subelement T5 - T5A
Which of the following describes alternating current?
Why is this correct?
Alternating current (AC) continuously changes direction, flowing first in one direction, then reversing to flow in the opposite direction. This creates the characteristic sine wave pattern where current alternates between positive and negative directions. Options A and B are incomplete - they only describe half of AC's behavior. AC doesn't just alternate with zero; it actively reverses direction through zero to flow the opposite way.
Memory tip
Look for the word 'alternates between' in AC questions - it signals a back-and-forth motion. AC always involves two opposite states or directions. When you see partial descriptions that mention only one direction or endpoint, they're typically incomplete distractors in AC-related questions.
Learn more
AC power in your home operates at 60 Hz, meaning current reverses direction 120 times per second (60 complete cycles). This constant directional change is why AC transformers work - the changing magnetic field from alternating current induces voltage in secondary windings. In amateur radio circuits, this same principle enables RF transformers, baluns, and antenna tuners to efficiently transfer RF energy across different impedance levels.
Think about it
Why do you think household electrical outlets use alternating current instead of the direct current that powers most electronic devices?