While charges consistently move in the same direction in a direct current, the flow of charges changes multiple times per second in an alternating current.

Visualize how alternating currents—electricity that periodically changes direction—are generated by rotating magnetic fields, as occurs in turbine-generator systems.

Tesla's alternating current power's most of the world's electric grids

In 1879, Thomas Edison’s light bulb relied on direct current, but such currents can't efficiently transmit power over long distances. Nikola Tesla introduced alternating current, which feature far fewer energy loses. Despite Edison’s attempts to discredit AC, Tesla proved its efficiency by lighting the 1893 Chicago World’s Fair.

The speed of electricity may refer to the movement of electrons, which is on the order of a fraction of a millimeter per second, or energy, which is near the speed of light.

Transformers change the current and voltage across a set of wires by wrapping them around a magnetic core and using the magnetic field of one wire to induce a current in the other.

Watch a timeline of the history of electricity, from observations of static electricity in antiquity to the War of the Currents—a rivalry to establish the ideal system for electric grids.

Alternating current was used to commit the first execution by electric chair

Dubbed the "executioner's current," the device was designed in Thomas Edison's lab by Harold Brown—an opponent of George Westinghouse and Nikola Tesla. The effort aimed at discrediting AC technology and gain favor for Thomas Edison's direct current as part of "The Current War."

Niagara Falls helped decide the battle between AC and DC power

In the 1890s, Niagara Falls became the proving ground for alternating current (AC) when Tesla and Westinghouse built the first large-scale AC hydroelectric plant—defeating Edison’s push for direct current (DC) in the US electrical system.

View the various types of lightning

The most common form of lightning involves channels of electricity between oppositely charged regions within a cloud or between two clouds to reestablish electrostatic equilibrium. While cloud-to-ground lightning is understood best, research is ongoing to fully model the mechanisms behind rarer forms of lightning, such as transient luminous events.

Thunder occurs when fast-flowing electricity heats and pressurizes air, causing it to expand and produce a shockwave at each point along the bolt at multiple frequencies.

Lightning forms when streams of rising and falling charged particles connect

In cloud-to-ground lightning, a buildup of negative charge at the bottom of clouds repels electrons on Earth's surface, leaving behind positively charged particles. When descending negatively charged air—the stepped leader—meets rising positively charged particles—the upward streamer—brightening runs up the connection, producing intense flashes known as return strokes.

Electricity can be lethal because it can disrupt the nervous system, which controls critical bodily functions that rely on electrical signals between cells, such as breathing and heart rate.

The engineering underlying the electric grid and why it needs to be modernized

The system includes generators for producing electricity and millions of miles of transmission and distribution lines to transport the energy. The substantial increase in the number of electronic devices and electrical demand since the construction of much of the grid in the mid-1900s has strained infrastructure, requiring continuous upgrades and massive investments in new construction.

Explore how excitatory cells, such as neurons and muscle cells, transmit information in the body via electrochemical signals, which can travel up to 120 meters (390 feet) per second.

Lightning is the sudden flow of electricity in the atmosphere as two oppositely charged regions seek to become balanced via the movement of electrons.

Watch lightning strike a building at 40,000 frames per second

When the built-up layer of negative charge at the bottom of clouds is sufficiently high, a network of charge filaments will emerge. If one of the filaments meets a rising strand of positively charged particles, a highly conductive path forms, and charges across all filaments move to the path, generating lightning

On average, every in-service airplane is struck by lightning once a year

The average strikes per surface area per year on Earth suggest that aircraft should only be struck once every 1,000 years, based on their size, but proximity to storm clouds' high electrical fields increases strike rates. Aircraft are designed as continuous conductive shells, causing electricity to flow along their exterior and preventing internal damage.

Wireless charging uses a magnetic field to move charged particles in a battery

Based on the concept of electromagnetic induction, when a compatible device is placed on a charging pad with correct alignment, the alternating current flowing through the pad creates a changing magnetic field. This magnetic field induces a current in the device, recharging the battery without a connecting wire.

Fluorescent bulbs can be illuminated by overhead power lines without making contact

The electromagnetic fields produced by the alternating current in transmission lines can induce the motion of charges in nearby objects. This motion yields electric currents that can light up bulbs but are too small to harm humans.

George Westinghouse purchased Tesla's AC technology patents for $60,000

The seven patents in alternating current motors and power transmission formed the basis for a system of technologies including generators, transformers, and lighting. Nikola Tesla spent half the funds on a new laboratory to develop new inventions.

As of 2025, China used the most electricity of any country, accounting for 33% of the total global demand and more than twice that of the US.

While gas-powered engines typically have 2,000 moving parts, electric vehicles have about 20.

Lightning rods provide a conductive pathway to safely steer massive electric currents

The device is positioned higher above the ground to "catch" one of the many branching filaments of electrons from clouds before they make contact with other surface structures, which have been induced to have a positive charge by overhead storm clouds. The current is then sent to a conductive grid buried underground.

Despite electric usage concerns, EV charging accounts for less than 1% of grid load

Other popular myths about EVs include battery failure concerns—failure rates are less than 1% on newer models—and that there are no places to charge cars, though both at-home outlets and more than 77,000 stations on the road are available.

Electricity is produced when the ends of a battery are connected by a conducting wire, triggering chemical reactions that release the energy stored in chemical bonds.

The most common type of particle accelerator is a linear electron accelerator, which fires particles in a straight line, making them useful for the intense, targeted beams needed in cancer treatment.

The gradual loss of capacity in rechargeable batteries can be delayed by avoiding overnight charging, charging to 100%, fast charging, and exposing your device to excessive heat.

Electricity can flow indefinitely along a ring of superconducting material, which provides zero resistance to the movement of charges due to quantum effects.

Thomas Edison publicly executed animals with AC to convince the public of its dangers

J.P. Morgan first backed Thomas Edison's direct current system, seeing electricity's potential to usurp John D. Rockefeller's kerosene empire. Despite the investments and smear campaign against alternating current, alternating current ultimately won public support after lighting the 1893 World's Fair, after which Morgan would fund Tesla's wireless transmission tower.

Simulate the buildup and discharge of static electricity through friction by dragging the arm and leg of 'John Travoltage' along surfaces.

Electromagnetic induction creates electricity from a changing magnetic field

The phenomenon was discovered in 1831 by Michael Faraday when an electric current was induced in a wire wrapped around an iron ring after a second wrapped wire not connected to the first was connected or disconnected from a battery.

On average, the human body produces about 100 watts of electricity—enough to power a light bulb—but some people can produce over 2,000 watts in short bursts, such as when sprinting.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Fluxgate magnetometers detect magnetic fields using electromagnets

Instead of a compass needle's movement indicating a magnetic field, an alternating current produces an oscillating magnetic field in a metal bar. An external magnetic field creates an imbalance in the oscillations, which can be measured quantitatively.

The unpredictability and brevity of lightning make lightning power impractical

While a typical lightning strike provides 30,000 amps at 300 million volts, the bolt only lasts about 30 microseconds. If the electrical surge could be captured—assuming one knew beforehand where it would strike—it would only provide enough electricity to power one home for about 6.4 hours.

Electrical grids worldwide must double their power delivery capacity by 2050 to meet surging demand from AI and electric vehicles.

The characteristic zigzag of lightning originates from columns of conductive oxygen

Energized electrons from the base of clouds collide with oxygen molecules, placing them in a "singlet delta state," which makes the air conductive. Collisions continue until more than 1% of nearby oxygen is in this state—about 0.00005 seconds—matching the electrical potential of the cloud and propogating electricity in a 50-meter "step."

Surface ocean currents are primarily driven by wind, tides, and Earth's rotation, while deep-ocean currents are driven by differences in temperature and salt concentration.

Charging an EV depends on power source, charger type and battery size

It takes less time to charge an electric vehicle's battery for Level 3 chargers, which can deliver 80% capacity in as little as 30 minutes. Level 1 chargers can take days. Larger vehicles possess larger batteries that increase charging time, despite often having less range.

How its uneven rotation produces the sun's 11-year cycle and flips its magnetic poles

While charged material rises and falls in the sun's convection zone, which induces magnetic fields, different latitudes rotate at different rates, making these fields increasingly turbulent. This builds to a critical point—the solar maximum—where magnetic field-driven events, such as solar flares, become more common before the field collapses and flips, restarting the cycle.

Batteries range in size based on their purpose, cost, and manufacturability

Lead-acid batteries used in combustion vehicles are resilient to temperature extremes, low-cost, and provide high surge current, which is needed for initial ignition. Alkaline batteries, including AA, AAA, and B, have long shelf lives and supply the low, steady power required for electronics with minimal demand fluctuations.

In the photovoltaic effect, light generates electricity by creating a charge imbalance after knocking electrons out of atoms in the semiconducting materials of solar cells.

Electrogenic animals generate their own electricity within an electric organ by changing the pattern of electrical charges in disc-shaped cells called electrocytes.

Lightning storms are more common in coastal and tropical regions

Water-abundant areas that receive increased solar radiation, such as those near the equator, experience increased rates of evaporation, which produce tall clouds as moisture rises, cools, and condenses. Mountain ranges can also steer air to higher altitudes, creating collisions between atmospheric particles that generate charge imbalances—the precursors to lightning.

If a source of music traveled past someone at twice the speed of sound, assuming sufficiently sensitive hearing and powerful equipment, they would hear the music backward.

How brain cells carry information

At any moment, there is an electrical storm coursing through your body. Discover how chemical reactions create an electric current that drives our responses to everything from hot pans to a mother’s caress.

Named after Nikola Tesla, who pioneered alternating current power systems, the Tesla coil was the first device to wirelessly transmit electricity.

View breakdowns of the world's and each nation's electricity comes from

These charts show how the shares of generated electricity sources—solar, wind, hydro, nuclear, bioenergy, oil, gas, and coal—have changed since 1985. Since 2010, an increase in renewable sources has offset the share lost by nuclear and fossil fuels.

The air around lightning can reach a temperature of about 30,000 degrees Celsius (54,000 degrees Fahrenheit)—five times hotter than the surface of the sun.

Mechanical watches measure the passage of time via the vibration of a quartz crystal

When electricity from a battery passes through the crystal inside a watch, the crystal vibrates, creating an electrical signal with a precise frequency of one vibration per second. This signal moves the hand of the watch so that it ticks once per second, allowing it to track the passage of time.

Light appears to slow down as it travels through different materials

As electromagnetic waves interact with particles in a transparent medium, particles vibrate and generate their own electromagnetic waves. The interference of the original and generated waves, which are slightly delayed, results in ensemble light with an effective slower speed but unchanged color.