Know the difference between direct current (d.c.) and alternating current (a.c.)

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IGCSE Physics - 4.2.2 Electric Current - DC vs AC

IGCSE Physics - 4.2.2 Electric Current

This section explores the fundamental difference between two types of electric current: direct current (d.c.) and alternating current (a.c.). Understanding these differences is crucial for comprehending how electricity is generated, transmitted, and used.

Direct Current (D.C.)

Definition

Direct current is the flow of electric charge in only one direction. The electric charge carriers (usually electrons) move consistently from the negative to the positive terminal of a power source.

Characteristics

  • Flows in one direction only.
  • Voltage is typically constant.
  • Commonly produced by batteries.
  • Used in portable electronic devices (e.g., mobile phones, laptops).

Diagram

Suggested diagram: A simple circuit with a battery, wire, and a light bulb showing the one-way flow of electrons.

Alternating Current (A.C.)

Definition

Alternating current is the flow of electric charge that periodically reverses direction. The direction of the electric current alternates at a regular frequency.

Characteristics

  • Direction of flow reverses periodically.
  • Voltage and current vary sinusoidally with time.
  • Typically produced by generators.
  • The standard current used for power distribution in homes and industries.

Diagram

Suggested diagram: A simple circuit with an AC power source, wire, and a light bulb showing the alternating direction of electron flow.

Comparison Table

Feature Direct Current (D.C.) Alternating Current (A.C.)
Direction of Flow One direction only Periodically reverses
Voltage Typically constant Varies sinusoidally
Source Batteries, solar cells Generators
Applications Portable electronics, electric vehicles (some) Household appliances, power grids
Transmission Efficiency Less efficient over long distances More efficient over long distances (can be stepped up to high voltages)

Key Differences Summarized

The fundamental difference between d.c. and a.c. lies in the direction of the electric current. D.c. flows in a single, constant direction, while a.c. reverses direction periodically. This difference leads to variations in how they are generated, transmitted, and used.