Wiktor Wise
An electric spark is an abrupt electrical discharge that occurs when a high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases. Lightning is an example of an electric spark in nature, and electric sparks are used in spark plugs in gasoline internal combustion engines to ignite fuel and air mixtures. An electric arc, on the other hand, is a continuous discharge that occurs in the gas-filled space between two conductive electrodes, resulting in a very high temperature capable of melting or vaporizing most materials. Electric arcs are used in various applications, such as lighting, manufacturing processes, and electric propulsion of spacecraft. While sparks and arcs share similarities as embodiments of `arc-discharge` phenomena, they differ in their initiation mechanisms, power sources, and voltage requirements.
| Characteristics | Values |
|---|---|
| Definition | An electrical spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. |
| An electric arc is a continuous discharge that occurs in the gas-filled space between two conductive electrodes. | |
| Occurrence | Sparks can occur within insulating liquids or solids, but with different breakdown mechanisms from sparks in gases. |
| Arcs can occur either in direct current (DC) circuits or in alternating current (AC) circuits. | |
| Visual Appearance | Sparks produce a brief emission of light and a sharp crack or snapping sound. |
| Arcs can come with heat and bright light. | |
| Initiation | Sparks can occur when the breakdown voltage for the air gap is exceeded and the gas is ionized enough to become relatively conductive. |
| Arcs are initiated by either thermionic-emission (T-Arc) or field-emission (F-Arc) and are maintained by a continuous supply of power. | |
| Persistence | Sparks are momentary discharges. |
| Arcs are continuous discharges that can survive short drops in power input. | |
| Power Source | Sparks require high voltage to occur. |
| Arcs require low voltage with normal or low pressure. | |
| Safety | Sparks can be dangerous and can cause fires and burn skin. |
| Arcs can be dangerous and are a major concern in HV power lines. | |
| Applications | Sparks are used in spark plugs, flame igniters, and metalworking. |
| Arcs are used in electric arc lighting, electric arc welding, and electric propulsion of spacecraft. |
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What You'll Learn
Sparks need high voltage to occur, arcs need low voltage
An electric spark occurs when there is a high potential energy between two conductors. This can be achieved by creating a high voltage or by breaking a large current in an inductive circuit. In the latter case, a spark is formed unintentionally when the contacts in an opening switch open and try to stop the current.
Arc welders, on the other hand, operate with comparatively low voltages (as low as 20V) but extremely high currents. To create an arc, the welder must first touch the material being welded with the electrode, and then pull the electrode away. This is known as "striking an arc".
The electric arc was discovered by Sir Humphry Davy in 1800. In his 1801 paper, he described the phenomenon as a spark rather than an arc. Arcing can also occur when a low-resistance channel forms between places with different voltages. This conductive channel can then facilitate the formation of an electric arc.
While arcs typically require lower voltages than sparks, the voltage is not the only factor influencing their formation. The distance between conductors also plays a role. If the conductors are very close together, even a lower voltage level can create a small arc. Similarly, reducing the distance between electrodes will increase the voltage required for an arc.
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Arcs are maintained by a continuous supply of power
While an electric spark and an electric arc share similarities, they are distinct phenomena with different characteristics and behaviours. An electric spark is an abrupt electrical discharge that occurs when a high electric field creates an ionized, electrically conductive channel through an insulating medium, typically air or other gases. Sparks can occur naturally, such as in lightning, or through human-made objects, like spark plugs in gasoline engines.
On the other hand, an electric arc is a continuous discharge that occurs in the gas-filled space between two conductive electrodes, often made of tungsten or carbon. Arcs result in extremely high temperatures, capable of melting or vaporizing most materials. They are utilized in various applications, including lighting, manufacturing processes such as welding, and electric propulsion in spacecraft.
The key difference between sparks and arcs lies in their initiation mechanisms and power sources. Sparks require high voltage to occur, while arcs operate with low voltage and normal or low pressure. Arcs are maintained by a continuous supply of power, relying on the thermionic emission of electrons from the electrodes. This means that even with short drops in power input, the arc can survive by drawing from the energy already dissipated from the current to keep the electrodes and arc's plasma hot.
For example, in AC networks or cheap transformer welding, the ionized conductive channel in an arc can withstand brief interruptions in power, ensuring the continuity of the discharge. This is in contrast to sparks, which are momentary and can extinguish within milliseconds if the power supply is disrupted.
The distinction between sparks and arcs is crucial for engineers, designers, and technicians working with electrical systems. Understanding these differences helps in effectively mitigating potential damage caused by contact current arcing and ensures the safe operation of electrical equipment.
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Sparks can occur within insulating liquids or solids
An electric spark is an abrupt electrical discharge that occurs when a high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases. This rapid transition from a non-conducting to a conductive state produces a brief emission of light and a sharp snapping sound.
Possible mechanisms for breakdown in liquids include bubbles, small impurities, and electrical super-heating. The process of breakdown in liquids is further complicated by hydrodynamic effects, as additional pressure is exerted on the fluid by the non-linear electrical field strength in the gap between the electrodes.
In both solids and liquids, the breakdown is influenced by the electrode material, the density of the material in the gap, and the size of the gap between the electrodes. The breakdown is also influenced by the sharp curvature of the conductor material, resulting in locally intensified electric fields.
Sparks can be hazardous to people, animals, and objects. They can ignite flammable materials, liquids, gases, and vapors. They can also cause damage to metals and other conductors, ablating or pitting the surface.
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Arcs can be extinguished by a blow of fresh air
An electric spark is an abrupt electrical discharge that occurs when a high electric field creates an ionized, electrically conductive channel through a normally insulating medium, often air or other gases. Sparks can be dangerous and can cause fires and burn skin. Lightning is an example of an electric spark in nature.
An electric arc is a continuous discharge that occurs in the gas-filled space between two conductive electrodes, often made of tungsten or carbon. The arc results in a very high temperature, capable of melting or vaporizing most materials. Electric arcs can be used for manufacturing processes such as electric arc welding, plasma cutting, and electric arc furnaces for steel recycling.
While sparks and arcs share similarities as embodiments of "'arc-discharge'" phenomena, there are important distinctions between them. Sparks need high voltage to occur, while arcs require low voltage with normal or low pressure. An arc is maintained by the thermionic emission of electrons from the electrodes, relying on energy already being dissipated from the current to heat the electrodes.
A spark can occur when the breakdown voltage for the air gap is exceeded and the gas becomes relatively conductive. Depending on the source parameters and geometry, the spark can then evolve into an arc as conductivity rises, or it can extinguish within milliseconds.
Arcs can be extinguished in multiple ways, including by a blow of fresh air or by their own updraft that stretches them too long to remain hot enough. This knowledge is crucial in HV power lines, where arcing poses a significant danger and must be prevented.
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Spark gap transmitters were widely used in the first three decades of radio
An electric arc is a continuous discharge that occurs in the gas-filled space between two conductive electrodes, often made of tungsten or carbon. The phenomenon was first discovered by Sir Humphry Davy in 1800, who described it in a paper published in 1801.
A spark gap transmitter is a device that generates radio waves by creating an electric spark across a spark gap. These transmitters were widely used in the first three decades of radio, from 1887 to the end of World War I. They were the first type of radio transmitter and were crucial for wireless telegraphy, also known as the "spark" era. German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, proving the existence of radio waves and studying their properties.
The design of spark gap transmitters was simple, and they were widely used on ships to communicate with shore stations and send distress calls. They played a vital role in maritime rescues, such as the 1912 RMS Titanic disaster. The operator would switch the transmitter on and off with a telegraph key, creating pulses of radio waves to transmit text messages. However, they had limitations; they could not transmit audio due to their inability to produce continuous waves. Their radio signals were also described as "noisy," causing interference with other radio transmissions.
Despite these shortcomings, spark gap transmitters were preferred by many operators due to their uncomplicated design and ease of control. However, with the development of vacuum tube transmitters after World War I, spark gap transmitters became obsolete by 1920. These new transmitters were less expensive, produced less interference, and could transmit audio, making them superior to their spark-gap predecessors.
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Frequently asked questions
An electrical spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures.
An electrical arc is a continuous discharge that occurs in the gas-filled space between two conductive electrodes. It results in a very high temperature, capable of melting or vaporizing most materials.
While sparks and arcs share similarities and the terms are sometimes used interchangeably, they are distinct phenomena. Sparks need high voltage to occur, while arcs need low voltage. Arcs can also survive short drops in power input, unlike sparks.
