An alternating current is one whose magnitude ______ and direction ______. 

Explanation:

Alternating Current

Definition: Alternating Current (AC) is a type of electrical current in which the magnitude of the current changes continuously and its direction reverses periodically. This behavior contrasts with Direct Current (DC), where the current flows steadily in one direction.

Working Principle:

In AC, the flow of electrons alternates between moving forward and backward within the conductor. This alternating behavior is caused by the periodic reversal of the voltage polarity across the circuit. The frequency of the AC determines how often the current reverses direction per second. For example, in most countries, the standard frequency of AC is 50 Hz or 60 Hz, meaning the current reverses direction 50 or 60 times per second.

Characteristics:

• Magnitude: The magnitude of AC varies continuously with time, typically following a sinusoidal waveform. The voltage and current rise and fall in a smooth, cyclic manner.
• Direction: The direction of AC changes periodically, reversing back and forth, unlike DC, which flows in a single direction.

Advantages:

• Efficient Power Transmission: AC can be easily transformed to higher or lower voltages using transformers, making it ideal for transmitting electricity over long distances with minimal losses.
• Wide Application: AC is the standard form of electricity used in homes, offices, and industries because most electrical devices and appliances are designed to work with AC.
• Flexible Generation: AC can be generated using devices like alternators, which are simpler and more efficient than DC generators for large-scale electricity production.

Disadvantages:

• Complexity in Circuits: AC circuits require additional components like capacitors and inductors to manage voltage and current, which makes them slightly more complex than DC circuits.
• Safety Concerns: Due to its alternating nature, AC can be more dangerous than DC at high voltages, as the periodic reversal can cause more severe effects on the human body.

Applications:

• Domestic and industrial power supply.
• Operation of electrical appliances such as fans, refrigerators, and televisions.
• Powering large-scale machinery and equipment in factories.

Correct Option Analysis:

The correct option is:

Option 1: Changes continuously; changes periodically

This option accurately describes the behavior of an alternating current. The magnitude of AC changes continuously, typically in a sinusoidal pattern, and the direction of current flow reverses periodically, following the frequency of the AC system.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Does not change; remains the same

This description corresponds to Direct Current (DC), not Alternating Current (AC). In DC circuits, the current flows steadily in one direction, and its magnitude remains constant over time. Therefore, this option is incorrect for describing AC.

Option 3: Does not change; changes periodically

This option is inconsistent. If the magnitude of the current does not change, it cannot be categorized as AC since the defining characteristic of AC is the continuous variation in magnitude and periodic reversal in direction. This statement is contradictory and does not apply to AC.

Option 4: Changes continuously; remains the same

This option partially describes the behavior of AC but fails to account for the periodic reversal of direction. While the magnitude of AC does change continuously, its direction also reverses periodically. Hence, this option is incomplete and incorrect.

Conclusion:

Understanding the fundamental characteristics of Alternating Current (AC) is essential for differentiating it from Direct Current (DC). The correct option, as explained, accurately captures the behavior of AC, where the magnitude changes continuously and the direction reverses periodically. This unique property makes AC suitable for widespread use in power transmission, domestic applications, and industrial operations, despite its associated complexities and safety considerations.