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alternating current
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A line graph showing peak current in amperes on the vertical axis versus angular frequency in units of ten thousand radians per second on the horizontal axis. The curve rises sharply to a peak near 3.5 on the horizontal axis, marked with a dotted line labeled omega sub r, then falls symmetrically. The background is light blue. sine wave A line graph displays a sinusoidal voltage wave described by V equals 170 cosine of 377t, with voltage on the vertical axis (ranging from -200 to 200 volts) and time in milliseconds on the horizontal axis (0 to 40 times 10 to the negative 3 seconds). Phase
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battery. Illustration of battery connected to lightbulb. Power a light bulb with a battery. Battery, Power Supply, Science, Circuit, Currents
Electricity: Short Circuits & Direct Currents
James Watt as a young man, c1769. Scottish engineer and instrument maker. Invented the modern steam engine which became the main source of power in Britain's textile mills. His engine had a separate condenser in which steam from the cylinder; (see notes)
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alternating current: References & Edit History

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  • The Editors of Encyclopaedia Britannica
    Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.

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Article History

Type Description Contributor Date
Invalidated site: Saskatchewan Open Education Resources - Introduction to Electricity, Magnetism, and Circuits - AC Sources. Nov 05, 2026
Add new Web site: OpenStax - University Physics Volume 2 - AC Sources. Aug 12, 2026
Add new Web site: National Center for Biotechnology Information - PubMed Central - Alternating Current Electric Fields of Varying Frequencies: Effects on Proliferation and Differentiation of Porcine Neural Progenitor Cells. Jun 19, 2026
Add new Web site: IOPSpark - Alternating current. Oct 03, 2025
Add new Web site: Physics LibreTexts - Alternating Currents. Aug 21, 2025
Add new Web site: MIT School of Engineering - What?s the difference between AC and DC? Jan 01, 2025
Add new Web site: Khan Academy - AC and DC generators. May 21, 2024
Add new Web site: DigitalCommons at University of Nebraska - Alternating Currents. Apr 12, 2024
Add new Web site: Energy Education - Alternating current. Jan 19, 2024
Add new Web site: Iowa State University Digital Press - Alternating Current. Dec 08, 2023
Add new Web site: Open Library Publishing Platform - PEG-3722 Electrotechnology - AC Voltage and Current. Oct 27, 2023
Add new Web site: Saskatchewan Open Education Resources - Introduction to Electricity, Magnetism, and Circuits - AC Sources. Aug 28, 2023
Add new Web site: UNESCO-EOLSS - Direct Current and Alternating Current Systems. Aug 25, 2023
Add new Web site: OpenStax - College Physics 2e - Alternating Current versus Direct Current. Sep 22, 2022
Added material about modern DC power transmission. Apr 02, 2021
Added material on advantages of AC over DC for power transmission. Jan 25, 2018
Added new Web site: Window To The Universe - Basic Facts About Direct (DC) And Alternating (AC) Current. May 11, 2009
Article revised and updated. Sep 22, 2006
Article added to new online database. Jul 20, 1998
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