Direct Current
Direct current (DC) is an electric current that flows consistently in one direction, with charge carriers (typically electrons) moving from the negative terminal to the positive terminal of a source. Unlike alternating current, the magnitude of DC does not periodically reverse; it may be steady or vary in magnitude but never changes polarity. DC is produced by batteries, fuel cells, solar cells, and rectifiers, and is essential in electronics, mobile devices, electric vehicles, and renewable energy storage systems.
Key Formula
P = I × V = I² × R = V² / R
LaTeX: P = IV = I^2 R = \frac{V^2}{R}
| Symbol | Meaning | Unit |
|---|---|---|
| P | Power dissipated or delivered | Watt (W) |
| I | Direct current | Ampere (A) |
| V | Voltage (potential difference) | Volt (V) |
| R | Resistance | Ohm (Ω) |
Worked Example
Problem
A 12 V DC car battery supplies a current of 5 A to a headlight bulb. Calculate the power consumed by the bulb and the resistance of the bulb filament.
Solution
Step 1: Calculate power using P = IV. P = 12 V × 5 A = 60 W Step 2: Calculate resistance using V = IR → R = V/I. R = 12 / 5 = 2.4 Ω Step 3: Verify using P = V²/R. P = (12)² / 2.4 = 144 / 2.4 = 60 W ✓
Answer
Power = 60 W; Filament resistance = 2.4 Ω
Comparison of Direct Current (DC) and Alternating Current (AC)
| Property | Direct Current (DC) | Alternating Current (AC) |
|---|---|---|
| Direction of flow | Unidirectional | Periodically reversing |
| Frequency | 0 Hz | 50 Hz (India), 60 Hz (USA) |
| Source examples | Battery, solar cell, fuel cell | Generator, mains supply |
| Voltage transformation | Difficult (requires converter) | Easy (transformer) |
| Power transmission efficiency | Lower at high voltage over distance | Higher over long distances |
| Primary applications | Electronics, EVs, storage | Mains power, industrial motors |
Interactive Tools
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Related Terms
Alternating Current
Alternating current (AC) is an electric current that periodically reverses direction, in contrast to direct current which flows only in one direction. The magnitude and direction of AC vary sinusoidally with time at a specific frequency — 50 Hz in India and most of the world, 60 Hz in North America. AC is the standard form of electrical power delivered to homes and industries because it can be efficiently stepped up or down in voltage using transformers, making long-distance transmission economical.
RMS Voltage
RMS (Root Mean Square) voltage is the effective value of an alternating voltage, defined as the square root of the mean of the squares of all instantaneous voltage values over one complete cycle. It represents the equivalent DC voltage that would deliver the same power to a resistive load as the AC voltage. For a sinusoidal AC supply, the RMS voltage equals the peak voltage divided by √2, which is why the 230 V delivered to Indian homes corresponds to a peak voltage of approximately 325 V.
Electric Dipole
An electric dipole consists of two equal and opposite electric charges (+q and −q) separated by a small distance (2a or d), characterised by the electric dipole moment — a vector quantity pointing from the negative to the positive charge. The dipole model is fundamental to understanding molecular polarity, dielectric materials, antenna radiation patterns, and the interaction of matter with electric fields. The electric field pattern of a dipole is more complex than that of a point charge, with field strength varying as 1/r³ at large distances.
"Direct" from Latin "directus" meaning "straight" or "aimed". "Current" from Latin "currens" (running). The term was popularised during Thomas Edison's promotion of DC power systems in the 1880s, contrasted with Tesla's AC systems.