Information:  - Induction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, through heat generated in the object by eddy currents (also called Foucault currents). An induction heater consists of an electromagnet, and an electronic oscillator that passes a high-frequency alternating current (AC) through the electromagnet. The rapidly alternating magnetic field penetrates the object, generating electric currents inside the conductor called eddy currents. The eddy currents flowing through the resistance of the material heat it by Joule heating. In ferromagnetic (and ferrimagnetic) materials like iron, heat may also be generated by magnetic hysteresis losses. The frequency of current used depends on the object size, material type, coupling (between the work coil and the object to be heated) and the penetration depth.  - Thermionic emission is the thermally induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the work function of the material. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as "thermions". After emission, a charge that is equal in magnitude and opposite in sign to the total charge emitted is initially left behind in the emitting region. But if the emitter is connected to a battery, the charge left behind is neutralized by charge supplied by the battery as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission.  - An oven is a thermally insulated chamber used for the heating, baking or drying of a substance, and most commonly used for cooking. Kilns and furnaces are special-purpose ovens, used in pottery and metalworking, respectively.  - A fuel is any material that can be made to react with other substances so that it releases chemical or nuclear energy as heat or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but has since also been applied to other sources of heat energy such as nuclear energy (via nuclear fission and nuclear fusion).  - An electric arc or arc discharge is an electrical breakdown of a gas that produces an ongoing electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An arc discharge is characterized by a lower voltage than a glow discharge, and it relies on thermionic emission of electrons from the electrodes supporting the arc. An archaic term is voltaic arc, as used in the phrase "voltaic arc lamp".  - Combustion or burning is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242 kJ/mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure):  - A glow discharge is a plasma formed by the passage of electric current through a low-pressure gas. It is created by applying a voltage between two metal electrodes in a glass tube containing gas. When the voltage exceeds a certain value called the striking voltage, the gas in the tube ionizes, becoming a plasma, and begins conducting electricity, causing it to glow with a colored light. The color depends on the gas used. Glow discharge is widely used as a source of light in devices such as neon lights, fluorescent lamps, and plasma-screen televisions. Analyzing the light produced by spectroscopy can reveal much about the atomic interactions in the gas, so glow discharge is used in plasma physics and analytical chemistry. It is also used in the surface treatment technique called sputtering.  - Electrical breakdown or dielectric breakdown is a long reduction in the resistance of an electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event (as in an electrostatic discharge), or may lead to a discontinuous arc charge if protective devices fail to interrupt the current in a low power circuit.  - A furnace is a device used for high-temperature heating. The name derives from Greek word "fornax", which means oven. The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces.  - An electric arc furnace ( EAF ) is a furnace that heats charged material by means of an electric arc . Industrial arc furnaces range in size from small units of approximately one ton capacity ( used in foundries for producing cast iron products ) up to about 400 ton units used for secondary steelmaking . Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams . Industrial electric arc furnace temperatures can be up to 1,800 ° C ( 3,272 ° F ) , while laboratory units can exceed 3,000 ° C ( 5,432 ° F ) . Arc furnaces differ from induction furnaces in that the charge material is directly exposed to an electric arc , and the current in the furnace terminals passes through the charged material .  - An induction furnace is an electrical furnace in which the heat is applied by induction heating of metal.  Induction furnace capacities range from less than one kilogram to one hundred tonnes capacity and are used to melt iron and steel, copper, aluminium and precious metals.  - An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, was the first practical electric light. It was widely used starting in the 1870s for street and large building lighting until it was superseded by the incandescent light in the early 20th century. It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II. The carbon arc lamp is now obsolete for all of these purposes and is only still made for very specialized purposes where a high intensity UV source is needed.    Given the information, choose the subject and object entities that have the relation of 'subclass of'.
electric arc furnace , oven