Which of the following describes alternating current?
The correct answer is C: Current that alternates between positive and negative directions. Alternating current (AC) is current that alternates between positive and negative directions - it flows in one direction, then reverses and flows in the opposite direction, repeating this cycle continuously.
AC current changes direction periodically, typically following a sine wave pattern. In one half of the cycle, current flows in the positive direction. In the next half, it flows in the negative direction. This alternation happens many times per second (60 times per second for 60 Hz AC power in the US). AC is different from DC (direct current), which flows in only one direction. Most household power is AC, and AC is used in many radio circuits for signal processing.
Exam Tip
AC = Alternates positive and negative. Remember: Alternating current alternates between positive and negative directions, not between positive/negative and zero.
Memory Aid
"**A**C = **A**lternates **C**ontinuously (think 'AC = AC' = Alternates Continuously, positive and negative)"
Real-World Application
Your household AC power (120 volts, 60 Hz) alternates 60 times per second. For half the cycle, current flows in the positive direction. For the other half, it flows in the negative direction. This alternation is what makes it 'alternating' current. Your power supply converts this AC to DC (which flows in only one direction) to power your transceiver.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. AC doesn't alternate between positive and zero. It alternates between positive and negative directions, going through both positive and negative values.
Option B: Incorrect. AC doesn't alternate between negative and zero. It alternates between positive and negative, not just negative and zero.
Option D: Incorrect. Not all answers are correct. Only option C correctly describes AC as alternating between positive and negative directions.
题目解析
The correct answer is C: Current that alternates between positive and negative directions. Alternating current (AC) is current that alternates between positive and negative directions - it flows in one direction, then reverses and flows in the opposite direction, repeating this cycle continuously. AC current changes direction periodically, typically following a sine wave pattern. In one half of the cycle, current flows in the positive direction. In the next half, it flows in the negative direction. This alternation happens many times per second (60 times per second for 60 Hz AC power in the US). AC is different from DC (direct current), which flows in only one direction. Most household power is AC, and AC is used in many radio circuits for signal processing.
考试技巧
AC = Alternates positive and negative. Remember: Alternating current alternates between positive and negative directions, not between positive/negative and zero.
记忆口诀
**A**C = **A**lternates **C**ontinuously (think 'AC = AC' = Alternates Continuously, positive and negative)
实际应用示例
Your household AC power (120 volts, 60 Hz) alternates 60 times per second. For half the cycle, current flows in the positive direction. For the other half, it flows in the negative direction. This alternation is what makes it 'alternating' current. Your power supply converts this AC to DC (which flows in only one direction) to power your transceiver.
错误选项分析
Option A: Incorrect. AC doesn't alternate between positive and zero. It alternates between positive and negative directions, going through both positive and negative values. Option B: Incorrect. AC doesn't alternate between negative and zero. It alternates between positive and negative, not just negative and zero. Option D: Incorrect. Not all answers are correct. Only option C correctly describes AC as alternating between positive and negative directions.
知识点
Alternating current, AC, Current direction, Electrical fundamentals
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.