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

• A. AC flows in one direction, while DC reverses direction
• B. AC varies over time, while DC flows consistently in one direction
• C. DC is used exclusively in residential wiring
• D. AC is only used for industrial applications

Answer: (B)

The correct answer highlights a fundamental characteristic of alternating current (AC) and direct current (DC). AC is known for its ability to vary in magnitude and direction over time, oscillating back and forth, which is a key feature of how it is generated and distributed for most power systems. This variation allows AC to be easily transformed to different voltages and is suitable for long-distance transmission, making it the standard for electrical grids.

In contrast, DC flows consistently in one direction. It maintains a constant polarity, providing a steady voltage and current flow. This is beneficial for many applications, including battery-powered devices, electronics, and electrochemical processes.

Other statements in the question do not accurately describe the core differences between AC and DC. The assertion that DC is used exclusively in residential wiring wrongly limits the scope of its application, as it is also utilized in many electronic devices and systems. Similarly, stating that AC is only used for industrial applications ignores its widespread use in residential settings as well, where it powers household appliances and lighting. Therefore, B encapsulates the essential difference between AC and DC, providing clarity about their respective behaviors in electrical circuits.