58. Alternating Current (AC) and Direct Current (DC)

1. Alternating Current (AC)

In an alternating current, the direction of the charge flow is constantly swapping back and forth.

  • Cause: It is produced by an alternating potential difference (voltage) that fluctuates between positive and negative.

  • UK Mains Supply: The electricity from our plug sockets is AC.

    • Frequency: 50 Hz (the direction changes 50 times per second).

    • Voltage: Approximately 230V or 240V (both are considered correct for exams).

  • Graph: On an oscilloscope, AC appears as a wave (sine wave) that goes above and below the zero line.

2. Direct Current (DC)

In a direct current, the charge always flows in the same direction.

  • Cause: It is produced by a direct potential difference that stays either positive or negative the entire time.

  • Sources: DC is found in cells and batteries, such as those used in mobile phones, calculators, and torches.

  • Graph: On an oscilloscope, DC appears as a straight horizontal line.

3. Measuring Current and Voltage

  • Oscilloscope: A device used to display potential difference vs. time graphs on a monitor, allowing scientists to see whether a current is AC or DC.

4. Comparison Summary

Feature

Alternating Current (AC)

Direct Current (DC)

Direction of Flow

Constantly reversing

Single direction

Potential Difference

Fluctuates (Pos/Neg)

Constant (Pos or Neg)

Typical Source

Mains electricity (plug sockets)

Cells and Batteries

UK Standard

230V / 50Hz

N/A (depends on battery)