The invention of refrigeration machines has meant an important advance in all aspects related to the conservation and transfer of fresh foods that need to be kept cold so that they last longer in their natural state, and in achieving adequate air conditioning in homes and public premises. Refrigeration machines are classified as freezers and refrigerators. Those for industrial use are located in companies, ships or trucks that work with frozen or refrigerated foods; In the domestic sphere, machines known as refrigerators and freezers are used, as well as air conditioning units that are present in many homes, varying in performance and capacity.

In 1784 William Cullen built the first cooling machine, but it was not until 1927 that the first domestic refrigerators were manufactured (by General Electric). Four years later, Thomas Midgley discovered freon, which due to its properties has since been widely used as a working fluid in cooling machines such as air conditioning equipment and refrigerators, both on an industrial and domestic scale. However, it has been shown that Freon and chemical compounds similar to it, also known as chlorofluorocarbons (CFCs), are the main causes of destruction in the ozone layer, producing the hole detected in Antarctica, which is why in 1987 the Montreal Protocol was signed to restrict the use of these compounds. Currently (2008) all refrigeration machines use refrigerant gases that do not harm the ozone layer.[2]​.

A refrigeration machine is a type of thermal generating machine that transforms some type of energy, usually mechanical, into thermal energy to obtain and maintain a temperature lower than the outside temperature in an area. The necessary mechanical energy can be previously obtained from another type of energy, such as electrical energy through an electric motor. This transfer is carried out using a refrigerant fluid or refrigerant, which in different parts of the machine undergoes pressure, temperature and phase transformations (liquid or gaseous); and which is placed in thermal contact with the enclosures to absorb heat from some areas and transfer it to others.

A refrigeration machine must contain at least the following four elements:.

In both the evaporator and the condenser, energy transfer is carried out mainly in the form of latent heat.

From an economic point of view, the best refrigeration cycle is the one that extracts the greatest amount of heat (Q2) from the cold source (T2) with the least work (W). Therefore, the efficiency of a refrigeration machine is defined as the ratio Q2/W:.

The refrigeration machine can be used as a heater (see Carnot Cycle). To do this, it is enough to make the hot focus the room, T1, and the cold focus the outside. It is the operating principle of the heat pump, which is more advantageous to use than electrical resistance heating. This dual function of producing cold and heat is used in modern air conditioning equipment that is installed in homes.

The French engineer Nicolas Léonard Sadi Carnot was the first to address the problem of the performance of a heat engine.

In Spain, all companies that are dedicated to activities related to refrigeration and air conditioning machines fall under the concept of industrial refrigeration and the professionals dedicated to these tasks are called refrigeration specialists. [3]​.

An electromagnet is a type of magnet "Magnet (physics)") in which the magnetic field is produced by the flow of an electric current, disappearing as soon as said current ceases. It was invented by British electrician William Sturgeon in 1825. Sturgeon could regulate his electromagnet, which marked the beginning of the use of electrical energy in useful and controllable machines, establishing the foundation for large-scale electronic communications.

The simplest type of electromagnet is a coiled piece of wire. A coil shaped like a straight tube (similar to a screw) is called a solenoid, and when it is also curved so that the ends coincide, it is called a toroid. Much stronger magnetic fields can be produced if a "core" of paramagnetic or ferromagnetic material (usually soft iron) is placed inside the coil. The core concentrates the magnetic field, which can then be much stronger than that of the coil itself.

The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly manipulated over a wide range by controlling the amount of electric current. However, a continuous source of electrical energy is needed to maintain the field. In applications where a variable magnetic field is not needed, permanent magnets are often superior. Additionally, these can be manufactured to produce stronger magnetic fields than electromagnets of similar size.

Electromagnets are used in many situations where a rapidly or easily varying magnetic field is needed. Many of these applications involve the deflection of beams of charged particles"), as in the cases of the cathode ray tube and the mass spectrometer.

Electromagnets are the essential components of many switches, being used in the electromagnetic brakes and clutches of automobiles. In some trams, electromagnetic brakes are attached directly to the rails. Very powerful electromagnets are used in cranes to lift heavy iron and steel blocks as well as containers, and to magnetically separate metals in scrapyards and recycling centers. Magnetic levitation trains use powerful electromagnets to float without touching the track and thus be able to travel at high speeds. Some trains use attractive forces, while others use repulsive forces.

Electromagnets are used in rotating electric motors to produce a rotating magnetic field") and in linear motors to produce a traveling magnetic field that drives the armature&action=edit&redlink=1 "Armor (electricity) (not yet written)"). Although silver is the best conductor of electricity, copper is the most often used material due to its low cost. Aluminum is sometimes used to reduce weight.

Calculating the force on ferromagnetic materials is, in general, quite complex. This is due to the contour field lines and complex geometries. It can be simulated using finite element analysis. However, it is possible to estimate the maximum force under specific conditions. If the magnetic field is confined within a highly permeable material, as is the case with certain steel alloys, the maximum force is given by:.

where:.

The area of ​​chemistry that studies the conversion between electrical energy and chemical energy is electrochemistry. Electrochemical processes are redox reactions where the energy released by a spontaneous reaction is transformed into electricity, or electricity is used to induce a non-spontaneous chemical reaction. This last process is known as electrolysis.

The word electrolysis comes from two radicals: electro which refers to electricity, and lysis, which means rupture. Electrolysis consists of the decomposition by means of an electric current of ionized substances called electrolytes. For example, in the electrolysis of water, oxygen (O) and hydrogen (H) are released.

Chemical reactions occur at the interface of an electrical conductor (called an electrode, which can be a metal or a semiconductor) and an ionic conductor (the electrolyte), which can be a solution and in some special cases, a solid. If a chemical reaction is conducted by an externally applied voltage, it is referred to as electrolysis. However, if the voltage or drop in electrical potential is created as a consequence of the chemical reaction, it is known as an "accumulator of electrical energy", also called a battery or galvanic cell.

At the end of the century (Illustration), the Italian anatomist and doctor Luigi Galvani marked the birth of electrochemistry in a scientific way by discovering that when electricity was passed through the legs of a dead frog they contracted, and when touching both ends of the nerves using the same scalpel but discharged nothing happened. Subsequently, the manufacturing of the first battery of modern times was carried out by Alessandro Volta. By the middle of the century, the modeling and study of electrochemistry were clarified by Michael Faraday (laws of electrolysis) and John Daniell (cell dependent only on zinc-copper metal ions). Starting in the 19th century, electrochemistry allowed the discovery of the charge of the electron by Millikan, and the establishment of Brønsted's modern theory of acids and bases. These contributions have allowed electrochemistry to be related today (2008) to topics as diverse as ranging from the quantum electrochemistry of Revaz Dogonadze or Rudolph A. Marcus, to photovoltaic cells and chemiluminescence.[5]​.

A solenoid valve is a device designed to control the flow of a fluid through a conduit such as a pipe. It is very commonly used in the hydraulic and pneumatic circuits of machinery and industrial facilities.

A solenoid valve has two fundamental parts: the solenoid and the valve. The solenoid converts electrical energy into mechanical energy to actuate the valve.

There are several types of solenoid valves. In some solenoid valves the solenoid acts directly on the valve, providing all the energy necessary for its movement. It is common for the valve to be kept closed by the action of a spring and for the solenoid to open it by overcoming the force of the spring.

It is also possible to build bistable solenoid valves that use one solenoid to open the valve and another to close or a single solenoid that opens with one impulse and closes with the next.

The solenoid valves can be closed at rest or normally closed which means that when the power supply fails they remain closed or they can be of the type open at rest or normally open which remain open when there is no power supply.

There are solenoid valves that, instead of opening and closing, what they do is bifurcate or divide the input between two outputs. These types of solenoid valves are often used in zone heating systems, allowing several zones to be heated independently using a single circulation pump.

In another type of solenoid valve, the solenoid does not control the valve directly, but rather the solenoid controls a secondary pilot valve and the energy to operate the main valve is supplied by the pressure of the fluid itself.[6]​.

Illumination or public lighting is the action or effect of illuminating public roads, monuments, highways, airports, sports venues, etc., using electricity, as well as the lighting of homes and especially workplaces when natural light conditions do not provide adequate visibility.

In technology, it refers to the set of lamps, light bulbs, "Focus (lighting)" spotlights, fluorescent tubes, among others, that are installed to produce the required lighting, both at practical and decorative levels. The aim of lighting is, first of all, to achieve a level of illumination, or illuminance, appropriate to the intended use of the illuminated space, the level of which will depend on the task that the users have to perform.

Lighting in workplaces must prevent visual fatigue from occurring"), which is caused if workplaces and traffic routes do not have sufficient lighting, whether natural or artificial, adequate and sufficient at night and when natural light is not sufficient.[7]​.

Premises, workplaces and traffic routes where workers are particularly exposed to risks in the event of failure of artificial lighting must have safety lighting of sufficient intensity and duration. Poor lighting causes visual fatigue in the eyes, damages the nervous system, degrades the quality of work and is responsible for a good part of work accidents.

Photometry "Photometry (optics)") is the science that is responsible for measuring light as the brightness perceived by the human eye. That is, it studies the ability of electromagnetic radiation to stimulate the visual system. In this area, illuminance is the amount of luminous flux emitted by a light source that hits, passes through or emerges from a surface per unit area. Its unit of measurement in the International System of Units is Lux: 1 Lux = 1 Lumen/m².

In general, illuminance is defined according to the following expression:

where:.

The following table shows the main photometric quantities, their unit of measurement and the associated radiometric quantity:

The candela is a basic SI unit. The remaining photometric units can be derived from basic units.

The British physicist James Prescott Joule discovered in the 1860s that if an electric current circulates in a conductor, part of the kinetic energy of the electrons is transformed into heat due to the collision they suffer with the molecules of the conductor through which they circulate, raising its temperature. This effect is known as the Joule effect in honor of its discoverer. This effect was defined as follows: "The amount of heat energy produced by an electric current depends directly on the square of the intensity of the current, the time it circulates through the conductor and the resistance that it opposes to the passage of the current." Mathematically it is expressed as.

where.

Thus, the power dissipated by the Joule effect will be:

where V is the potential difference between the ends of the conductor.

Microscopically the Joule effect is calculated through the volume integral of the electric field times the current density:.

Resistance is the component that transforms electrical energy into heat energy. This effect is the basis for the operation of different household appliances that take advantage of heat in their performance - braziers, toasters, hair dryers, heaters, etc. - and some devices used industrially - soldering irons, industrial ovens, etc. - in which the useful effect sought is precisely the heat given off by the conductor due to the passage of current. However, in most applications of electricity it is an unwanted effect and the reason why electrical and electronic devices need a fan to dissipate the heat generated and prevent excessive heating of the different devices.[8]​.

One of the most important and transcendental innovations in the production of all types of objects in the second half of the century has been the incorporation of robots, programmable automata and machines guided by Computer Numerical Control (CNC) in production chains and machines, mainly in tasks related to the manipulation, transfer of objects, machining and welding processes. These technological innovations have been viable, among other things, due to the design and construction of new generations of direct current electric motors controlled by electronic input and output signals and the rotation they can have in both directions, as well as the variation of their speed, in accordance with the instructions contained in the computer program that controls them. Three types of electric motors are used in these machines: stepper motors, servomotors or encoder motors), and linear motors.[9]​

Robotics is a branch of technology that studies the design and construction of machines capable of performing repetitive tasks, tasks that require high precision, dangerous tasks for humans, or tasks that cannot be performed without the intervention of a machine. The sciences and technologies on which it is based are, among others, algebra, programmable automata, state machines, mechanics, electronics and computing.

A robot is defined as a man-made entity and an intelligent feedback connection between sense and direct action under the control of a computer previously programmed with the tasks it has to perform. The actions of these types of robots are generally carried out by motors or actuators that move limbs or propel the robot. Around 1942, Isaac Asimov gives a humanized version through his well-known series of stories, in which he introduces for the first time the term robotics in the sense of a scientific discipline in charge of building and programming robots. Furthermore, this author suggests that the actions carried out by a robot must be directed by a series of moral rules, called the Three Laws of Robotics.[10]​.

Robots are used today (2008) to carry out dirty, dangerous, difficult, repetitive or dull tasks for humans. This usually takes the form of an industrial robot used on production lines. Other applications include toxic waste cleanup, space exploration, mining, human search and rescue, and landmine location. Manufacturing continues to be the main market where robots are used. In particular, articulated robots (similar in movement capacity to a human arm) are the most commonly used. Applications include welding, painting and machinery loading. The automotive industry has taken great advantage of this new technology where robots have been programmed to replace the work of humans in many repetitive tasks. Recently, a breakthrough has been made in robots dedicated to medicine that uses state-of-the-art robots in minimally invasive surgery procedures. Laboratory automation is also a growing area. Robots continue to become cheaper and smaller in size, thanks to the miniaturization of the electronic components used to control them. Also, many robots are designed in simulators long before they are built and interact with real physical environments.

Safety signage is called a set of signs that, referring to a specific object, activity or situation, provides an indication or an obligation related to safety or health at work by means of a sign in the form of a panel, a color, a light or acoustic signal, a verbal communication or a gestural signal, as appropriate.[11]​.

There are two types of light signals: those that act intermittently and those that act continuously. The light signals have the following color code:.

When an intermittent light signal is used, the duration and frequency of the flashes must allow the correct identification of the message, preventing it from being perceived as continuous or confused with other light signals.

A traffic light is an electrical device that regulates vehicle and pedestrian traffic at intersections of urban roads that support a lot of traffic. Traffic lights are also used on train tracks to regulate convoy traffic on the tracks. The most common type has three colored lights:

It was in 1914 when the first electric traffic light was installed in Cleveland (United States). It had red and green lights, placed on arm-shaped supports, and also incorporated a buzzer.

Traffic lights have evolved over time and currently (2008) LED lamps are being used for light signaling, since LED lamps use only 10% of the energy consumed by incandescent lamps, have an estimated lifespan 50 times longer, and therefore generate significant energy and maintenance savings, satisfying the objective of achieving greater reliability and public safety.

The LED optics are composed of a printed circuit board, protective polycarbonate, E-27 screw cap, all of these elements integrated on a conical support.

Domestic use of electricity refers to its use in homes. The main uses are lighting, appliances, heating and air conditioning. Research is being carried out to produce electrical appliances that have the highest possible energy efficiency, just as it is necessary to improve the conditioning of homes in terms of insulation from the outside to reduce electricity consumption when using heating or air conditioning, which are the appliances with the highest electrical consumption.

Appliances are called all machines or electrical devices that perform routine domestic tasks, such as cooking, preserving food or cleaning, both for a home and for institutions, businesses or industries. Household appliances are commercially classified into three groups:

In the countries of the European Union, manufacturers of household appliances are obliged to label their products with the so-called energy label"), in order to contribute to energy savings and the preservation of the environment.

The energy label is an informative tool that indicates the amount of energy consumed by an appliance and the efficiency with which it uses that energy, in addition to other complementary data about the appliance. There are seven types of energy labels that are classified, depending on electrical consumption, in different colors and with letters of the alphabet from A (most efficient) to G (least efficient). In this way, users can evaluate and compare the energy performance of different models of the same type of appliance at the time of purchase. Comparisons can only be made between appliances of the same type. For example, the electrical consumption of a class A washing machine is not comparable with that of a dishwasher of the same class, but it is comparable with that of another class C washing machine.

The label must always be visible on the exposed device. In cases of sales by catalog, on the Internet or by any other means where the consumer cannot see the appliances in person, the energy performance described on the label must also be included.

The household appliances that, according to European Union regulations, must carry an energy label are the following: refrigerators, freezers and combined appliances, washing machines, dryers and washer-dryers, dishwashers, light sources, air conditioners, electric ovens, water heaters and other appliances that store hot water.[12]​.

The main consumers of electricity are industries, highlighting those that have large electric furnaces installed in their production processes, such as steel, cement, ceramic and chemical factories. Electrolysis processes (production of chlorine and aluminum) and seawater desalination plants are also large consumers.

In some countries, for example Spain, there are special supply contracts with these large electricity consumers who are granted a very low rate in exchange for the possibility of cutting off their electricity supply (which forces them to go into a technical stoppage), when the weather forecasts predict heat waves or intense cold waves, to avoid supply saturation due to high domestic consumption of air conditioning or heating. These large consumers also operate their most powerful ovens at night when the electricity rate is lower. In the Spanish case, the use of these special rates could be prohibited by the European Commission, considering them unfair incentives at the expense of other electricity users.[13]​.

Industries also consume electricity to provide electric lighting when natural lighting is not possible, in order to prevent "eye fatigue" in workers, which occurs if workplaces and traffic routes do not have sufficient, adequate and sufficient lighting at night.[14]​.

Another general field of electrical consumption in companies is that dedicated to the activation of air conditioning and heating machines. The electricity consumption in this chapter can be very high if the facilities are not built in accordance with ecological energy saving principles.

Likewise, the electricity used in different types of electric welding, electrolysis processes, industrial electric ovens used in many different tasks, among others, is of industrial use.

A sensitive field of electricity use in companies or institutions is the permanent power supply and constant voltage that computer installations must have, because an unforeseen power outage can damage the work being done at the time of the outage. To avoid this damage, there are emergency devices that momentarily alleviate the absence of electricity supply in the network.

Electricity plays a determining role in the operation of all types of vehicles that run on internal combustion engines. To produce the electricity that these vehicles need for their operation, they incorporate a small alternator that is driven by a pulley transmission from the engine crankshaft shaft. They also have a battery that serves as a reserve of electricity so that it is possible to start the engine when it is stopped, activating the starter motor. The most important electrical components of a transport vehicle are the following: alternator, battery, lighting equipment, ignition equipment, starter motor, signaling and emergency equipment, control instruments, among others.

The replacement of internal combustion engines with electric motors is an issue not yet resolved, mainly due to the low capacity of the batteries and the slow charging process as well as their limited autonomy. Progress is being made in the launch of hybrid cars with a double operating system: a thermal combustion engine that charges accumulators and electric motors that drive the traction on the wheels.

A field where the application of electric machines has been completely successful has been in the operation of railways.

The electrification process has been developed in two phases. The first was the replacement of locomotives that used coal with so-called diesel locomotives that used diesel. Diesel-electric locomotives basically consist of two components, a diesel engine that drives an electric generator, and several electric motors (known as traction motors) that communicate the tractive force that moves the locomotive to the wheels. Traction motors are powered with electrical current and then, through gears, drive the wheels.

The introduction of direct electric locomotives constituted an important technological advance. Electric locomotives are those that use electrical energy from an external source as a source of energy, to apply it directly to electric traction motors. These locomotives require the installation of power cables along the entire route, which are located at a height above the trains in order to avoid accidents. This installation is known as catenary "Catenary (railway)"). The locomotives receive electricity through a trolley, which is most often shaped like a pantograph and is known as such. In the 1980s, asynchronous motors were integrated as propellants for electric railway vehicles, and electronic power regulation systems appeared, giving definitive support to the choice of this type of traction by railway companies. The milestone of electric trains is the so-called high-speed trains, whose development has been as follows:

Despite the development of direct electric locomotives, diesel locomotives continue to be used in large areas of the planet.

On November 8, 1895, German physicist Wilhelm Conrad Röntgen discovered that when electrons moving at high speed collide with matter, they give rise to a highly penetrating form of radiation. This radiation was called X radiation and its discovery is considered one of the most extraordinary in the science of signaling and emergency, control instruments, among others.

The operating rooms and rehabilitation and intensive care units (ICU) or (ICU) have been equipped with high-tech electronic and computer equipment. Radiation therapy uses ionizing radiation to treat cancer.

Recently, a breakthrough has been made in robots dedicated to medicine that uses state-of-the-art robots in minimally invasive surgery procedures. Laboratory automation is also a growing area. Robots continue to become cheaper and smaller in size, thanks to the miniaturization of the electronic components used to control them. Also, many robots are designed in simulators long before they are built and interact with real physical environments.

Finally, electricity has made it possible to improve clinical analysis instruments and techniques, for example through high-resolution electron microscopes.

The invention of refrigeration machines has meant an important advance in all aspects related to the conservation and transfer of fresh foods that need to be kept cold so that they last longer in their natural state, and in achieving adequate air conditioning in homes and public premises. Refrigeration machines are classified as freezers and refrigerators. Those for industrial use are located in companies, ships or trucks that work with frozen or refrigerated foods; In the domestic sphere, machines known as refrigerators and freezers are used, as well as air conditioning units that are present in many homes, varying in performance and capacity.

In 1784 William Cullen built the first cooling machine, but it was not until 1927 that the first domestic refrigerators were manufactured (by General Electric). Four years later, Thomas Midgley discovered freon, which due to its properties has since been widely used as a working fluid in cooling machines such as air conditioning equipment and refrigerators, both on an industrial and domestic scale. However, it has been shown that Freon and chemical compounds similar to it, also known as chlorofluorocarbons (CFCs), are the main causes of destruction in the ozone layer, producing the hole detected in Antarctica, which is why in 1987 the Montreal Protocol was signed to restrict the use of these compounds. Currently (2008) all refrigeration machines use refrigerant gases that do not harm the ozone layer.[2]​.

A refrigeration machine is a type of thermal generating machine that transforms some type of energy, usually mechanical, into thermal energy to obtain and maintain a temperature lower than the outside temperature in an area. The necessary mechanical energy can be previously obtained from another type of energy, such as electrical energy through an electric motor. This transfer is carried out using a refrigerant fluid or refrigerant, which in different parts of the machine undergoes pressure, temperature and phase transformations (liquid or gaseous); and which is placed in thermal contact with the enclosures to absorb heat from some areas and transfer it to others.

A refrigeration machine must contain at least the following four elements:.

In both the evaporator and the condenser, energy transfer is carried out mainly in the form of latent heat.

From an economic point of view, the best refrigeration cycle is the one that extracts the greatest amount of heat (Q2) from the cold source (T2) with the least work (W). Therefore, the efficiency of a refrigeration machine is defined as the ratio Q2/W:.

The refrigeration machine can be used as a heater (see Carnot Cycle). To do this, it is enough to make the hot focus the room, T1, and the cold focus the outside. It is the operating principle of the heat pump, which is more advantageous to use than electrical resistance heating. This dual function of producing cold and heat is used in modern air conditioning equipment that is installed in homes.

The French engineer Nicolas Léonard Sadi Carnot was the first to address the problem of the performance of a heat engine.

In Spain, all companies that are dedicated to activities related to refrigeration and air conditioning machines fall under the concept of industrial refrigeration and the professionals dedicated to these tasks are called refrigeration specialists. [3]​.

An electromagnet is a type of magnet "Magnet (physics)") in which the magnetic field is produced by the flow of an electric current, disappearing as soon as said current ceases. It was invented by British electrician William Sturgeon in 1825. Sturgeon could regulate his electromagnet, which marked the beginning of the use of electrical energy in useful and controllable machines, establishing the foundation for large-scale electronic communications.

The simplest type of electromagnet is a coiled piece of wire. A coil shaped like a straight tube (similar to a screw) is called a solenoid, and when it is also curved so that the ends coincide, it is called a toroid. Much stronger magnetic fields can be produced if a "core" of paramagnetic or ferromagnetic material (usually soft iron) is placed inside the coil. The core concentrates the magnetic field, which can then be much stronger than that of the coil itself.

The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly manipulated over a wide range by controlling the amount of electric current. However, a continuous source of electrical energy is needed to maintain the field. In applications where a variable magnetic field is not needed, permanent magnets are often superior. Additionally, these can be manufactured to produce stronger magnetic fields than electromagnets of similar size.

Electromagnets are used in many situations where a rapidly or easily varying magnetic field is needed. Many of these applications involve the deflection of beams of charged particles"), as in the cases of the cathode ray tube and the mass spectrometer.

Electromagnets are the essential components of many switches, being used in the electromagnetic brakes and clutches of automobiles. In some trams, electromagnetic brakes are attached directly to the rails. Very powerful electromagnets are used in cranes to lift heavy iron and steel blocks as well as containers, and to magnetically separate metals in scrapyards and recycling centers. Magnetic levitation trains use powerful electromagnets to float without touching the track and thus be able to travel at high speeds. Some trains use attractive forces, while others use repulsive forces.

Electromagnets are used in rotating electric motors to produce a rotating magnetic field") and in linear motors to produce a traveling magnetic field that drives the armature&action=edit&redlink=1 "Armor (electricity) (not yet written)"). Although silver is the best conductor of electricity, copper is the most often used material due to its low cost. Aluminum is sometimes used to reduce weight.

Calculating the force on ferromagnetic materials is, in general, quite complex. This is due to the contour field lines and complex geometries. It can be simulated using finite element analysis. However, it is possible to estimate the maximum force under specific conditions. If the magnetic field is confined within a highly permeable material, as is the case with certain steel alloys, the maximum force is given by:.

where:.

The area of ​​chemistry that studies the conversion between electrical energy and chemical energy is electrochemistry. Electrochemical processes are redox reactions where the energy released by a spontaneous reaction is transformed into electricity, or electricity is used to induce a non-spontaneous chemical reaction. This last process is known as electrolysis.

The word electrolysis comes from two radicals: electro which refers to electricity, and lysis, which means rupture. Electrolysis consists of the decomposition by means of an electric current of ionized substances called electrolytes. For example, in the electrolysis of water, oxygen (O) and hydrogen (H) are released.

Chemical reactions occur at the interface of an electrical conductor (called an electrode, which can be a metal or a semiconductor) and an ionic conductor (the electrolyte), which can be a solution and in some special cases, a solid. If a chemical reaction is conducted by an externally applied voltage, it is referred to as electrolysis. However, if the voltage or drop in electrical potential is created as a consequence of the chemical reaction, it is known as an "accumulator of electrical energy", also called a battery or galvanic cell.

At the end of the century (Illustration), the Italian anatomist and doctor Luigi Galvani marked the birth of electrochemistry in a scientific way by discovering that when electricity was passed through the legs of a dead frog they contracted, and when touching both ends of the nerves using the same scalpel but discharged nothing happened. Subsequently, the manufacturing of the first battery of modern times was carried out by Alessandro Volta. By the middle of the century, the modeling and study of electrochemistry were clarified by Michael Faraday (laws of electrolysis) and John Daniell (cell dependent only on zinc-copper metal ions). Starting in the 19th century, electrochemistry allowed the discovery of the charge of the electron by Millikan, and the establishment of Brønsted's modern theory of acids and bases. These contributions have allowed electrochemistry to be related today (2008) to topics as diverse as ranging from the quantum electrochemistry of Revaz Dogonadze or Rudolph A. Marcus, to photovoltaic cells and chemiluminescence.[5]​.

A solenoid valve is a device designed to control the flow of a fluid through a conduit such as a pipe. It is very commonly used in the hydraulic and pneumatic circuits of machinery and industrial facilities.

A solenoid valve has two fundamental parts: the solenoid and the valve. The solenoid converts electrical energy into mechanical energy to actuate the valve.

There are several types of solenoid valves. In some solenoid valves the solenoid acts directly on the valve, providing all the energy necessary for its movement. It is common for the valve to be kept closed by the action of a spring and for the solenoid to open it by overcoming the force of the spring.

It is also possible to build bistable solenoid valves that use one solenoid to open the valve and another to close or a single solenoid that opens with one impulse and closes with the next.

The solenoid valves can be closed at rest or normally closed which means that when the power supply fails they remain closed or they can be of the type open at rest or normally open which remain open when there is no power supply.

There are solenoid valves that, instead of opening and closing, what they do is bifurcate or divide the input between two outputs. These types of solenoid valves are often used in zone heating systems, allowing several zones to be heated independently using a single circulation pump.

In another type of solenoid valve, the solenoid does not control the valve directly, but rather the solenoid controls a secondary pilot valve and the energy to operate the main valve is supplied by the pressure of the fluid itself.[6]​.

Illumination or public lighting is the action or effect of illuminating public roads, monuments, highways, airports, sports venues, etc., using electricity, as well as the lighting of homes and especially workplaces when natural light conditions do not provide adequate visibility.

In technology, it refers to the set of lamps, light bulbs, "Focus (lighting)" spotlights, fluorescent tubes, among others, that are installed to produce the required lighting, both at practical and decorative levels. The aim of lighting is, first of all, to achieve a level of illumination, or illuminance, appropriate to the intended use of the illuminated space, the level of which will depend on the task that the users have to perform.

Lighting in workplaces must prevent visual fatigue from occurring"), which is caused if workplaces and traffic routes do not have sufficient lighting, whether natural or artificial, adequate and sufficient at night and when natural light is not sufficient.[7]​.

Premises, workplaces and traffic routes where workers are particularly exposed to risks in the event of failure of artificial lighting must have safety lighting of sufficient intensity and duration. Poor lighting causes visual fatigue in the eyes, damages the nervous system, degrades the quality of work and is responsible for a good part of work accidents.

Photometry "Photometry (optics)") is the science that is responsible for measuring light as the brightness perceived by the human eye. That is, it studies the ability of electromagnetic radiation to stimulate the visual system. In this area, illuminance is the amount of luminous flux emitted by a light source that hits, passes through or emerges from a surface per unit area. Its unit of measurement in the International System of Units is Lux: 1 Lux = 1 Lumen/m².

In general, illuminance is defined according to the following expression:

where:.

The following table shows the main photometric quantities, their unit of measurement and the associated radiometric quantity:

The candela is a basic SI unit. The remaining photometric units can be derived from basic units.

The British physicist James Prescott Joule discovered in the 1860s that if an electric current circulates in a conductor, part of the kinetic energy of the electrons is transformed into heat due to the collision they suffer with the molecules of the conductor through which they circulate, raising its temperature. This effect is known as the Joule effect in honor of its discoverer. This effect was defined as follows: "The amount of heat energy produced by an electric current depends directly on the square of the intensity of the current, the time it circulates through the conductor and the resistance that it opposes to the passage of the current." Mathematically it is expressed as.

where.

Thus, the power dissipated by the Joule effect will be:

where V is the potential difference between the ends of the conductor.

Microscopically the Joule effect is calculated through the volume integral of the electric field times the current density:.

Resistance is the component that transforms electrical energy into heat energy. This effect is the basis for the operation of different household appliances that take advantage of heat in their performance - braziers, toasters, hair dryers, heaters, etc. - and some devices used industrially - soldering irons, industrial ovens, etc. - in which the useful effect sought is precisely the heat given off by the conductor due to the passage of current. However, in most applications of electricity it is an unwanted effect and the reason why electrical and electronic devices need a fan to dissipate the heat generated and prevent excessive heating of the different devices.[8]​.

One of the most important and transcendental innovations in the production of all types of objects in the second half of the century has been the incorporation of robots, programmable automata and machines guided by Computer Numerical Control (CNC) in production chains and machines, mainly in tasks related to the manipulation, transfer of objects, machining and welding processes. These technological innovations have been viable, among other things, due to the design and construction of new generations of direct current electric motors controlled by electronic input and output signals and the rotation they can have in both directions, as well as the variation of their speed, in accordance with the instructions contained in the computer program that controls them. Three types of electric motors are used in these machines: stepper motors, servomotors or encoder motors), and linear motors.[9]​

Robotics is a branch of technology that studies the design and construction of machines capable of performing repetitive tasks, tasks that require high precision, dangerous tasks for humans, or tasks that cannot be performed without the intervention of a machine. The sciences and technologies on which it is based are, among others, algebra, programmable automata, state machines, mechanics, electronics and computing.

A robot is defined as a man-made entity and an intelligent feedback connection between sense and direct action under the control of a computer previously programmed with the tasks it has to perform. The actions of these types of robots are generally carried out by motors or actuators that move limbs or propel the robot. Around 1942, Isaac Asimov gives a humanized version through his well-known series of stories, in which he introduces for the first time the term robotics in the sense of a scientific discipline in charge of building and programming robots. Furthermore, this author suggests that the actions carried out by a robot must be directed by a series of moral rules, called the Three Laws of Robotics.[10]​.

Robots are used today (2008) to carry out dirty, dangerous, difficult, repetitive or dull tasks for humans. This usually takes the form of an industrial robot used on production lines. Other applications include toxic waste cleanup, space exploration, mining, human search and rescue, and landmine location. Manufacturing continues to be the main market where robots are used. In particular, articulated robots (similar in movement capacity to a human arm) are the most commonly used. Applications include welding, painting and machinery loading. The automotive industry has taken great advantage of this new technology where robots have been programmed to replace the work of humans in many repetitive tasks. Recently, a breakthrough has been made in robots dedicated to medicine that uses state-of-the-art robots in minimally invasive surgery procedures. Laboratory automation is also a growing area. Robots continue to become cheaper and smaller in size, thanks to the miniaturization of the electronic components used to control them. Also, many robots are designed in simulators long before they are built and interact with real physical environments.

Safety signage is called a set of signs that, referring to a specific object, activity or situation, provides an indication or an obligation related to safety or health at work by means of a sign in the form of a panel, a color, a light or acoustic signal, a verbal communication or a gestural signal, as appropriate.[11]​.

There are two types of light signals: those that act intermittently and those that act continuously. The light signals have the following color code:.

When an intermittent light signal is used, the duration and frequency of the flashes must allow the correct identification of the message, preventing it from being perceived as continuous or confused with other light signals.

A traffic light is an electrical device that regulates vehicle and pedestrian traffic at intersections of urban roads that support a lot of traffic. Traffic lights are also used on train tracks to regulate convoy traffic on the tracks. The most common type has three colored lights:

It was in 1914 when the first electric traffic light was installed in Cleveland (United States). It had red and green lights, placed on arm-shaped supports, and also incorporated a buzzer.

Traffic lights have evolved over time and currently (2008) LED lamps are being used for light signaling, since LED lamps use only 10% of the energy consumed by incandescent lamps, have an estimated lifespan 50 times longer, and therefore generate significant energy and maintenance savings, satisfying the objective of achieving greater reliability and public safety.

The LED optics are composed of a printed circuit board, protective polycarbonate, E-27 screw cap, all of these elements integrated on a conical support.

Domestic use of electricity refers to its use in homes. The main uses are lighting, appliances, heating and air conditioning. Research is being carried out to produce electrical appliances that have the highest possible energy efficiency, just as it is necessary to improve the conditioning of homes in terms of insulation from the outside to reduce electricity consumption when using heating or air conditioning, which are the appliances with the highest electrical consumption.

Appliances are called all machines or electrical devices that perform routine domestic tasks, such as cooking, preserving food or cleaning, both for a home and for institutions, businesses or industries. Household appliances are commercially classified into three groups:

In the countries of the European Union, manufacturers of household appliances are obliged to label their products with the so-called energy label"), in order to contribute to energy savings and the preservation of the environment.

The energy label is an informative tool that indicates the amount of energy consumed by an appliance and the efficiency with which it uses that energy, in addition to other complementary data about the appliance. There are seven types of energy labels that are classified, depending on electrical consumption, in different colors and with letters of the alphabet from A (most efficient) to G (least efficient). In this way, users can evaluate and compare the energy performance of different models of the same type of appliance at the time of purchase. Comparisons can only be made between appliances of the same type. For example, the electrical consumption of a class A washing machine is not comparable with that of a dishwasher of the same class, but it is comparable with that of another class C washing machine.

The label must always be visible on the exposed device. In cases of sales by catalog, on the Internet or by any other means where the consumer cannot see the appliances in person, the energy performance described on the label must also be included.

The household appliances that, according to European Union regulations, must carry an energy label are the following: refrigerators, freezers and combined appliances, washing machines, dryers and washer-dryers, dishwashers, light sources, air conditioners, electric ovens, water heaters and other appliances that store hot water.[12]​.

The main consumers of electricity are industries, highlighting those that have large electric furnaces installed in their production processes, such as steel, cement, ceramic and chemical factories. Electrolysis processes (production of chlorine and aluminum) and seawater desalination plants are also large consumers.

In some countries, for example Spain, there are special supply contracts with these large electricity consumers who are granted a very low rate in exchange for the possibility of cutting off their electricity supply (which forces them to go into a technical stoppage), when the weather forecasts predict heat waves or intense cold waves, to avoid supply saturation due to high domestic consumption of air conditioning or heating. These large consumers also operate their most powerful ovens at night when the electricity rate is lower. In the Spanish case, the use of these special rates could be prohibited by the European Commission, considering them unfair incentives at the expense of other electricity users.[13]​.

Industries also consume electricity to provide electric lighting when natural lighting is not possible, in order to prevent "eye fatigue" in workers, which occurs if workplaces and traffic routes do not have sufficient, adequate and sufficient lighting at night.[14]​.

Another general field of electrical consumption in companies is that dedicated to the activation of air conditioning and heating machines. The electricity consumption in this chapter can be very high if the facilities are not built in accordance with ecological energy saving principles.

Likewise, the electricity used in different types of electric welding, electrolysis processes, industrial electric ovens used in many different tasks, among others, is of industrial use.

A sensitive field of electricity use in companies or institutions is the permanent power supply and constant voltage that computer installations must have, because an unforeseen power outage can damage the work being done at the time of the outage. To avoid this damage, there are emergency devices that momentarily alleviate the absence of electricity supply in the network.

Electricity plays a determining role in the operation of all types of vehicles that run on internal combustion engines. To produce the electricity that these vehicles need for their operation, they incorporate a small alternator that is driven by a pulley transmission from the engine crankshaft shaft. They also have a battery that serves as a reserve of electricity so that it is possible to start the engine when it is stopped, activating the starter motor. The most important electrical components of a transport vehicle are the following: alternator, battery, lighting equipment, ignition equipment, starter motor, signaling and emergency equipment, control instruments, among others.

The replacement of internal combustion engines with electric motors is an issue not yet resolved, mainly due to the low capacity of the batteries and the slow charging process as well as their limited autonomy. Progress is being made in the launch of hybrid cars with a double operating system: a thermal combustion engine that charges accumulators and electric motors that drive the traction on the wheels.

A field where the application of electric machines has been completely successful has been in the operation of railways.

The electrification process has been developed in two phases. The first was the replacement of locomotives that used coal with so-called diesel locomotives that used diesel. Diesel-electric locomotives basically consist of two components, a diesel engine that drives an electric generator, and several electric motors (known as traction motors) that communicate the tractive force that moves the locomotive to the wheels. Traction motors are powered with electrical current and then, through gears, drive the wheels.

The introduction of direct electric locomotives constituted an important technological advance. Electric locomotives are those that use electrical energy from an external source as a source of energy, to apply it directly to electric traction motors. These locomotives require the installation of power cables along the entire route, which are located at a height above the trains in order to avoid accidents. This installation is known as catenary "Catenary (railway)"). The locomotives receive electricity through a trolley, which is most often shaped like a pantograph and is known as such. In the 1980s, asynchronous motors were integrated as propellants for electric railway vehicles, and electronic power regulation systems appeared, giving definitive support to the choice of this type of traction by railway companies. The milestone of electric trains is the so-called high-speed trains, whose development has been as follows:

Despite the development of direct electric locomotives, diesel locomotives continue to be used in large areas of the planet.

On November 8, 1895, German physicist Wilhelm Conrad Röntgen discovered that when electrons moving at high speed collide with matter, they give rise to a highly penetrating form of radiation. This radiation was called X radiation and its discovery is considered one of the most extraordinary in the science of signaling and emergency, control instruments, among others.

The operating rooms and rehabilitation and intensive care units (ICU) or (ICU) have been equipped with high-tech electronic and computer equipment. Radiation therapy uses ionizing radiation to treat cancer.

Recently, a breakthrough has been made in robots dedicated to medicine that uses state-of-the-art robots in minimally invasive surgery procedures. Laboratory automation is also a growing area. Robots continue to become cheaper and smaller in size, thanks to the miniaturization of the electronic components used to control them. Also, many robots are designed in simulators long before they are built and interact with real physical environments.

Finally, electricity has made it possible to improve clinical analysis instruments and techniques, for example through high-resolution electron microscopes.