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ASVAB · Components and Devices

What is the difference between AC (alternating current) and DC (direct current)?

Correct answer

DC flows in one direction only; AC periodically reverses direction — in the US, household AC reverses direction 120 times per second (60 Hz)

  1. A AC is stronger than DC
  2. B DC flows in one direction only; AC periodically reverses direction — in the US, household AC reverses direction 120 times per second (60 Hz)
  3. C AC is used only in batteries; DC is used in power lines
  4. D They are the same except for voltage level

Why this is the answer

DC (Direct Current): Electrons flow in one consistent direction — positive terminal to negative terminal (conventional current). Source: batteries, solar cells, fuel cells. Used in: all electronics, electric vehicles, USB devices. AC (Alternating Current): Direction of electron flow reverses periodically. US standard: 60 Hz (60 cycles per second = 120 direction reversals/second); European standard: 50 Hz. Used in: power grid transmission (more efficient for long-distance), motors, household appliances. CONVERSION: DC → AC: Inverter; AC → DC: Rectifier (diodes). The power adapter for your laptop converts AC wall power to DC for the device.
Source: ASVAB EI, AC vs DC

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