## Electric & magnetic fields

Electric and magnetic fields are two aspects of the same fundamental force, the electromagnetic force. The electromagnetic force is responsible for the attraction and repulsion between electrically charged particles, as well as for the propagation of light and other forms of electromagnetic radiation.

• First of all, let’s clarify the connection between force and field in this definition.
• A force is a push or pull on an object. A field is a region of space in which a force acts on objects.
• In the case of the electromagnetic force, the electric field is the region of space in which electric forces act on charged particles, and the magnetic field is the region of space in which magnetic forces act on moving charged particles.
• In other words, electric and magnetic fields are the regions in space where the electromagnetic force pushes and pulls microscopic objects such as electrons and macroscopic objects such as magnets or metal filings.
##### Interconnection of Electric and Magnetic Fields
• Electric and magnetic fields are interconnected, and changes in one field can induce changes in the other.
• Electromagnetic waves are produced when electric and magnetic fields oscillate together.
• A change in an electric field induces a change in the magnetic field.
• A change in a magnetic field induces a change in the electric field.
##### Propagation of Electromagnetic Waves
• Once an electromagnetic wave radiates outward, it generally remains unaffected by external electric or magnetic fields. This is because electromagnetic waves are not composed of particles in the same way that matter is. They are more accurately described as disturbances in the electromagnetic field.
• There are exceptions to this rule:
• If an electromagnetic wave passes through an immensely strong magnetic field, it may experience slight deflection.
• Another exception is the deflection of electromagnetic waves by gravitational fields. However, gravitational deflection of light only takes place in the presence of objects like galaxies and black holes.
##### Nature of Electromagnetic Waves
• It’s important to note that electromagnetic waves do not require a medium to propagate through. This characteristic is related to the nature of photons.
• Photons are elementary particles that constitute electromagnetic radiation, meaning that electromagnetic radiation can be viewed as a stream of photons.
• While electromagnetic waves can travel through a vacuum, they can also interact with and be affected by matter when they pass through different materials.
• This interaction with matter forms the basis for various applications in optics, communications, and imaging, where electromagnetic waves interact with substances like glass, metals, or biological tissues.
##### Electromagnetic induction
• Whilst the material above focuses on the connection between electric and magnetic fields and light, let us quickly summarise their connection to the generation and utilization of electrical energy.
• In the most simple terms, electromagnetic induction is a way of converting mechanical energy into electrical energy and vice versa. by moving a magnet near a wire or changing the magnetic field around a wire.
• When a magnet is moved near a wire, it creates a changing magnetic field around the wire. This changing magnetic field induces an electric current in the wire. The direction and magnitude of the induced current depend on the direction and speed of the moving magnet, as well as the orientation of the wire.
• Electromagnetic induction can also be used to convert electrical energy into mechanical energy. This is achieved using motors. Motors use electromagnetic induction to generate a rotating force, which can then be used to power devices like fans, pumps, compressors, or electric vehicles.

Electromagnetic waves consist of coupled oscillating electric and magnetic fields orientated at 900 to one another.

• An electric field is created by a change in voltage (charge). The higher the voltage the stronger the field.
• Electric and magnetic fields are two aspects of the same fundamental force, the electromagnetic force. The electromagnetic force is responsible for the attraction and repulsion between electrically charged particles, as well as for the propagation of light and other forms of electromagnetic radiation.
• The connection between force and field in this definition can be summarized as:
• A force is a push or pull on an object. A field is a region of space in which a force acts on objects.
• In the case of the electromagnetic force, the electric field is the region of space in which electric forces act on charged particles, and the magnetic field is the region of space in which magnetic forces act on moving charged particles.
• In other words, electric and magnetic fields are the regions in space where the electromagnetic force pushes and pulls microscopic objects such as electrons and macroscopic objects such as magnets or metal filings.

## Electric and magnetic fields

Electric and magnetic fields are fundamental forces responsible for generating and transmitting electromagnetic radiation, including visible light.

## Electric charge

• Electric charge is the physical property of matter that causes it to experience a force when it interacts with an electromagnetic field.
• An electric charge can be positive or negative. Like charges repel each other while opposite charges attract.
• An object without charge is termed neutral.
• When two objects with the same charge approach each other, they experience a repulsive force, causing them to move apart.
• If two objects with opposite charges are brought together, they encounter an attractive force that draws them closer.
• Electric charge is a fundamental property of matter, but it is not fully understood how it originates.
• It is believed that electric charge is related to the spin of subatomic particles.
• Electric charge is quantized, meaning it exists in discrete units, and the smallest unit of charge is carried by a single electron or proton.

## Electric charge

• Electric charge is an inherent property of matter at all scales, from the subatomic to the macroscopic.
• At the subatomic level, electric charge is carried by elementary particles, such as electrons, protons, and neutrons. Electrons have a negative charge, while protons have a positive charge. Neutrons have no charge.
• Electron (-)
• Protons (+)
• Neutron (o)
• At the atomic level, electric charge is determined by the number of protons and electrons in an atom.
• An atom with the same number of protons and electrons is electrically neutral.
• An atom with more protons than electrons is positively charged.
• An atom with more electrons than protons is negatively charged.
• At the macroscopic level, electric charge is determined by the net charge of all the atoms and molecules in an object.
• An object with a net positive charge is positively charged.
• An object with a net negative charge is negatively charged.
• Here are some examples of electric charge at different scales:
##### Subatomic
• An electron has a negative charge, and a proton has a positive charge.
• The charge of a subatomic particle cannot change. Elementary particles, such as electrons, protons, and neutrons, have a fixed charge that is determined by their intrinsic properties. For example, an electron will always have a negative charge, and a proton will always have a positive charge.
##### Atomic
• Only atoms with a net imbalance of protons and electrons have a charge. If an atom has the same number of protons and electrons, it is electrically neutral.
• The number of protons in an atom determines its element and ots atomic number, but the number of electrons can change. This is because atoms can lose or gain electrons to become ions.

• The atomic number is a unique identifier for each element, and it is listed in the periodic table. The number of electrons in an atom is determined by its electron configuration. The electron configuration is a description of how the electrons in an atom are arranged in energy levels.

• Atoms can lose or gain electrons to become ions. An ion is a charged atom. If an atom loses electrons, it becomes a positively charged ion called a cation. If an atom gains electrons, it becomes a negatively charged ion called an anion.

• A sodium atom has a net positive charge because it has more protons than electrons. A chlorine atom has a net negative charge because it has more electrons than protons.

##### Macroscopic
• A rubber balloon that has been rubbed on hair is negatively charged. A metal rod that has been rubbed with fur is positively charged.
• Electric charge plays a role in many aspects of physics, including electromagnetism, chemistry, and particle physics. It is responsible for the formation of atoms and molecules, the propagation of light, and the behaviour of magnets. Charge is also used to generate electricity.
• Charge is a quantized property, meaning that it can only exist in discrete units. The smallest unit of charge is the elementary charge, which is denoted by the symbol e. The elementary charge is approximately equal to 1.602 × 10⁻¹⁹ coulombs.
• Charge is conserved, meaning that the total amount of charge in an isolated system cannot change. This means that when charged particles interact with each other, they can either exchange charge or transfer charge, but the total amount of charge in the system remains the same.
• Here are some examples of charge in physics:
• The electrons in an atom have a negative charge, while the protons in the nucleus have a positive charge. The attraction between the oppositely charged particles holds the atom together.
• The current in an electric circuit is caused by the flow of electrons.
• A lightning bolt is a massive discharge of electricity caused by the build-up of charge in the atmosphere.
• The Northern Lights are caused by the interaction of charged particles from the Sun with the Earth’s atmosphere.
###### References
• 1
• 2
• Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be positive or negative. Like charges repel each other and unlike charges attract each other. An object with no net charge is referred to as electrically neutral.
• Electric charge is an inherent property of matter at all scales, from the subatomic to the macroscopic.
• At the subatomic level, electric charge is carried by elementary particles, such as electrons, protons, and neutrons. Electrons have a negative charge, while protons have a positive charge. Neutrons have no charge.
• Electron (-)
• Protons (+)
• Neutron (o)
• At the atomic level, electric charge is determined by the number of protons and electrons in an atom.
• An atom with the same number of protons and electrons is electrically neutral.
• An atom with more protons than electrons is positively charged.
• An atom with more electrons than protons is negatively charged.

## Electric charge and energy in an atom

###### About electric charge and energy in an atom
• An atom has a set number of particles that determines what kind of element they are.
• Each element has a specific number of protons (positive charge) in its nucleus. It is this number that defines an element and cannot change in everyday situations.
• Protons in the nucleus of an atom are very stable and don’t typically move around or get created or destroyed. There are a fixed number and they maintain their positive charge within the atom.
• Electrons (negative charge) surround the nucleus, with the number typically matching the number of protons to create a neutral atom.
• Regardless of their energy level, an atom retains the same number of electrons it started with.
• If an atom loses or gains an electron, it is no longer considered the same element and becomes an ion.
• The movement of electrons within an atom doesn’t change their total charge because the number of protons and electrons remains constant. However, the movement of electrons does affect the amount of energy within the atom.
• Electrons in an atom change energy levels as they gain and lose energy.
• So when an electron absorbs energy (such as visible light), it jumps to a higher energy level further away from the nucleus. However, the electron itself remains negatively charged, it just occupies a different position within the atom.

## Electric field

Dynamic electric fields are a property of photons.  Dynamic electric fields (along with dynamic magnetic fields) are responsible for the transmission of electromagnetic energy, such as visible light.

• Photons are massless particles that carry electromagnetic energy. A photon is a quantum of light.
• The electric fields produced by photons are oscillating, meaning their strength varies between maximum and minimum values over time.
• The frequency of the electric field determines the frequency of the photon. The higher the frequency of the photon, the shorter the wavelength of the photon.

## Electric field line

An electric field line is a component of a diagram representing an electric field. It is a line that corresponds with the electric field at every point along its length. The direction of the electric field line shows the direction of the electric field.

• Drawing field lines to show an electric field is a way of visualizing the direction and strength of the field at given points in space.
• Electric field lines point away from their origin at a positively charged object and towards their termination at a negatively charged object.
• At a sub-atomic scale, the electric field around a positively charged particle (such as a proton) is directed away from the charge, and the electric field around a negative charge particle (such as an electron) is directed towards the charge.
• The density of field lines is used to represent the strength of the electric field, with more lines indicating a stronger field.
##### Drawing field lines
• To draw electric field lines, start by placing a point where you want to visualise the direction of the field between a positively charged and a negatively charged ball bearing.
• The direction of electric field lines between them can be established using a small compass. A compass needle experiences a torque that causes it to align with the electric field.
• By placing a compass needle near an object with a positive or negative, you can trace out the electric field lines by following the direction of the compass needle.
• For example, if you place a compass needle near a positive charge, the compass needle will point towards the charge. This is because positive charges attract electrons, and the electrons in the compass needle will be attracted to the positive charge. If you trace out the direction of the compass needle at different points and connect them you will be tracing out the electric field lines.
###### References
• An electric field line is a component of a diagram representing an electric field. It is a line that corresponds with the electric field at every point along its length.
• The direction of the electric field line shows the direction of the electric field.
• Drawing field lines to show an electric field is a way of visualizing the direction and strength of the field at given points in space.
• Electric field lines point away from their origin at a positively charged object and towards their termination at a negatively charged object.
• At a sub-atomic scale, the electric field around a positively charged particle (such as a proton) is directed away from the charge, and the electric field around a negative charge particle (such as an electron) is directed towards the charge.
• The density of field lines is used to represent the strength of the electric field, with more lines indicating a stronger field.

## Electrically charged particle

An electrically charged particle is a particle that has a positive or negative charge. Electrically charged particles are associated with the electromagnetic force, which is one of the four fundamental forces of nature. The electromagnetic force is responsible for the attraction and repulsion between electrically charged particles, as well as for the propagation of light and other electromagnetic radiation.

• All electrically charged particles interact with each other through the electromagnetic force. The strength of the interaction depends on the magnitude of the charges and the distance between the particles.
• Two types of electrically charged particles are associated with electromagnetic force: elementary particles and composite particles.
• Elementary particles: These particles are not made up of sub-particles. They are the fundamental building blocks of matter. Electrons, photons, and neutrinos are all elementary particles.
• Composite particles: These particles are made up of sub-particles. Protons and neutrons are composite particles. They are made up of quarks, which are also elementary particles.
• All particles, except for those with no charge, have a positive or negative charge.
• Particles with opposite charges (+ and -) are attracted towards one another by the electric force.
• Particles with the same charge (+ and +, or – and -) are repelled away from one another by the electric force.
• The charge of a particle is a property that is intrinsic to the particle. It cannot be created, destroyed, or changed.
##### Electrically charged particles within atoms
• Within atoms:
• Electrons (elementary particles) have a negative charge of -1. Electrons are responsible for the negative charge of atoms. They are found in the outermost shell of atoms.
• Protons (composite particles) have a positive charge of +1. They are found in the nucleus of atoms, along with neutrons. Protons are responsible for the positive charge of atoms.
• Neutrons (composite particles) have no charge. They are found in the nucleus of atoms, along with protons. Neutrons are responsible for the mass of atoms. Neutrons can decay into protons and electrons, which means that they can acquire a charge.
• Atoms are electrically neutral, meaning that they have an equal number of protons and electrons. The protons have a positive charge, the electrons have a negative charge and neutrons have no charge. The negative charge of the electrons cancels out the positive charge of the protons.
• There are some exceptions to this rule. For example, atoms of some elements can lose or gain electrons, which can make them electrically charged. These atoms are called ions.
###### References
• An electrically charged particle is a particle that has a positive or negative charge.
• Electrically charged particles are associated with the electromagnetic force, which is one of the four fundamental forces of nature.
• The electromagnetic force is responsible for the attraction and repulsion between electrically charged particles, as well as for the propagation of light and other electromagnetic radiation.
• All electrically charged particles interact with each other through the electromagnetic force. The strength of the interaction depends on the magnitude of the charges and the distance between the particles.
• All particles, except for those with no charge, have a positive or negative charge.
• Particles with opposite charges (+ and -) are attracted towards one another by the electric force.
• Particles with the same charge (+ and +, or – and -) are repelled away from one another by the electric force.
• The charge of a particle is a property that is intrinsic to the particle. It cannot be created, destroyed, or changed.

## Electroluminescence

Electroluminescence (EL) refers to the phenomenon where light is emitted as a direct result of an applied electric field. Unlike other luminescence mechanisms that rely on chemical reactions or light absorption, electroluminescence is driven solely by the electrical energy itself.

##### Key features of electroluminescence
• Energy source: An electric field directly interacts with electrons, exciting them to higher energy levels.
• Electron transitions: Excited electrons return to their ground state, releasing excess energy as light (determining the colour).
• Materials: Certain materials like semiconductors and phosphors are susceptible to electroluminescence under electric fields.
##### Applications of electroluminescence
• Lighting technologies: LEDs, OLEDs, and EL displays use this principle for efficient lighting.
• Sensors and indicators: Some sensors and indicator lights rely on electroluminescence for visual signalling.
• Back-lighting: Electroluminescent panels can be used for back-lighting in devices like LCD screens.
##### Mechanisms involved in electroluminescence
• Injection electroluminescence: An electric field injects electrons or holes into a material, leading to recombination and light emission (common in LEDs and OLEDs).
• Impact excitation: High-energy electrons collide with atoms or molecules, exciting them and causing light emission (used in some EL displays).

In the context of electroluminescence, “recombination” refers to the process where an excited electron and a “hole” (absence of an electron) reunite within a material, releasing energy as light.

Components

• Excited electron: An electron within the material absorbs energy (often from an electric field) and occupies a higher-energy state.
• Hole: Not a physical particle, but the absence of an electron in a specific location within an atom, acting like a positive charge seeking an electron.

The Process

1. Injection: An electric field introduces electrons or holes into the material.
2. Movement: These injected particles move through the material.
3. Encounter: An excited electron and a hole meet within the material.
4. Recombination: They “recombine,” meaning the electron fills the hole, returning to its ground state.
5. Energy release: During recombination, the excess energy is released as a photon of light, causing electroluminescence.

Key Points

• Emitted light colour depends on the energy difference between the electron’s excited and ground states.
• Recombination is crucial for converting electrical energy into light in LEDs, OLEDs, and other electroluminescent devices.
Light sources
Emission mechanism DescriptionExamples
LIGHT-EMITTING PROCESS
LuminescenceLight emission due to the excitation of electrons in a material.Electrons within a material gain energy and then release light as they return to a lower energy state.Bioelectroluminescence
Electroluminescence
Photoluminescence
- Fluorescence
- Phosphorescence
Sonoluminescence
Thermoluminescence
Blackbody radiation (Type of thermal radiation)Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero.Electromagnetic radiation (including visible light) emitted by any object with a temperature above absolute zero.All objects above temperature of absolute zero.
ChemiluminescenceLight from natural and artificial chemical reactions.Light from natural and artificial chemical reactions.Bioluminescence
Chemiluminescent reactions:
- Luminol reactions
- Ruthenium chemiluminescence
Nuclear reactionLight emission as a byproduct of nuclear reactions (fusion or fission).Light emitted as a byproduct of nuclear reactions.Nuclear reactors
Stars undergoing fusion
Thermal radiationLight emission due to the thermal excitation of atoms and molecules at high temperatures.Light emission due to the thermal excitation of atoms and molecules.Sun
Stars
Incandescent light bulbs
TriboluminescenceLight emission due to mechanical stress applied to a material.Light emission due to the mechanical stress applied to a material, causing the movement of electric charges and subsequent light emission.Sugar crystals cracking
Quartz crystals fracturing.
Natural light source
Fireflies
Deep-sea creatures
Glowing mushrooms
Bioluminescence Light emission from biological organisms.Involves the luciferase enzyme.
Sun
Stars
Nuclear FusionLight emission as a byproduct of nuclear fusion reactions in stars.Electromagnetic spectrum (visible light, infrared, ultraviolet).
Fire
Candles
Thermal radiationLight emission due to the thermal excitation of atoms and molecules during the combustion of a fuel source.Burning of a fuel source, releasing heat and light.
Artificial light source
Fluorescent lights Highlighters
Safety vests
Chemiluminescence Light emission from chemical reactions.Fluorescence (absorption and re-emission of light).
Glow sticks
Emergency signs
ChemiluminescenceLight emission due to phosphorescence - a type of chemiluminescence.A type of chemiluminescence where light emission is delayed after the initial excitation.
Glow sticks
Light sticks
Chemiluminescence Chemiluminescence Light emission from a chemical reaction that does not involve combustion.
Tungsten light bulbs
Toasters
Thermal radiationHeated filament radiates light and heat.Light emission from a hot filament.
Fluorescent lamps
LED lights
ElectroluminescenceExcitation of atoms by electric current.Light emission when electric current excites atoms in a material.
Neon signsElectrical DischargeDischarge of electricity through gas.Light emission when electricity flows through a gas.
Sugar crystals cracking
TriboluminescenceLight emission from friction or pressure.Light emission due to mechanical forces.
Fluorescent paint Highlighters
Safety vests
PhotoluminescenceAbsorption and subsequent re-emission of light at a lower energy.Absorption and re-emission of light.

Light Sources: Mechanism, examples, and everyday applications

Footnote: Cerenkov radiation and Synchrotron radiation are not included in the table because they are not conventionally classified as light sources.

###### References
• Electroluminescence (EL) refers to the phenomenon where light is emitted as a direct result of an applied electric field. Unlike other luminescence mechanisms that rely on chemical reactions or light absorption, electroluminescence is driven solely by the electrical energy itself.
##### Key features of electroluminescence
• Energy source: An electric field directly interacts with electrons, exciting them to higher energy levels.
• Electron transitions: Excited electrons return to their ground state, releasing excess energy as light (determining the colour).
• Materials: Certain materials like semiconductors and phosphors are susceptible to electroluminescence under electric fields.

## Electromagnetic energy

Electromagnetic energy refers to the energy transported by electromagnetic waves.

##### Photons and electromagnetic energy
• Photons are discrete packets of energy that make up electromagnetic waves.
• The energy of each photon is directly proportional to its frequency and inversely proportional to its wavelength.
• The energy of electromagnetic radiation can be calculated as the total number of photons multiplied by the energy of each photon.
##### Electromagnetic waves and electromagnetic energy
• Electromagnetic waves can be described in terms of their electric and magnetic fields.
• The electric and magnetic fields of the wave do not carry energy in the same way that photons do.
• Electric and magnetic fields are a manifestation of the energy carried by the wave.
• In other words, the energy of the wave is distributed between the electric and magnetic fields, which are intimately linked and cannot be separated from each other.
• The electric and magnetic fields of the wave do not exist independently of the wave, but rather they are a fundamental part of the wave itself.
##### Measuring electromagnetic energy
• The energy of electromagnetic waves can be measured using various techniques, depending on the frequency range of the wave being studied.
• In the radio frequency range, measurement requires antennas and receivers capable of converting the electrical energy of the wave into a measurable signal, such as a voltage or a current.
• In the optical and ultraviolet frequency ranges, measurement requires detectors such as photo-diodes or photomultiplier tubes, which convert the energy of individual photons into a measurable electrical signal.
• In the X-ray and gamma-ray frequency ranges,  measurement requires specialized detectors such as scintillation counters or Geiger-Müller tubes, which are capable of detecting individual high-energy photons.
• The energy of an individual photon can be calculated using the Planck-Einstein relation, which relates the energy of a photon to its frequency or wavelength. This means that the energy of an electromagnetic wave can be calculated as the product of the number of photons and the energy of each photon.
• In many practical applications, it is more convenient to measure the power (or intensity) of the electromagnetic wave rather than its energy.
• Power is measured in units of watts, and intensity is measured in units of watts per square meter.

## Electromagnetic field

An electromagnetic field is a more comprehensive entity than its individual electric and magnetic field components.

## Electromagnetic field

An electromagnetic field is a physical field that describes the behaviour of electrically charged particles and their interactions. It is a region of space where electric and magnetic forces are present. These fields are created by the presence or movement of electrically charged particles.

##### Electromagnetic field and particle physics

The electromagnetic field and the electromagnetic force are two different aspects of electromagnetism.

• The electromagnetic force is one of the four fundamental forces of nature. It is the force that acts between charged particles.
• The electromagnetic field is the field that mediates the electromagnetic force. It is a physical field that exists throughout space, and it is created by charged particles.
• This means that the electromagnetic field is how the electromagnetic force is transmitted.
• The electromagnetic field is a real physical field, just like the gravitational field.
• When two charged particles such as electrons interact, they do so through the electromagnetic field.
• The electromagnetic field is a two-component field. It has an electric component and a magnetic component. The electric field is created by charges, while the magnetic field is created by moving charges. The two fields are closely related, and they can be converted into each other.
• The electromagnetic field is agitated by charged particles:
• When a charged particle moves, it creates a disturbance in the electromagnetic field. This disturbance propagates through the field as a particle-wave, a photon.
• Photons are particles of light and are responsible for the transmission of light energy.
• The faster a charge moves, the stronger the electromagnetic field it creates. This is why magnets can attract and repel each other.
• The electromagnetic field carries the force, in the form of the momentum and energy of a photon, between the particles, and it is the field that determines how the particles interact.
• The electromagnetic field is present everywhere in the universe and manifests in many ways:
• At the subatomic level, the electromagnetic field is responsible for the forces between charged particles.
• At the atomic level, it is responsible for the bonding of atoms and molecules.
• At the macroscopic level, it is responsible for light, electricity, and magnetism.
• The electromagnetic field is a continuum, which means that there are no sharp boundaries between different regions of the field. It is a smooth, wave-like field that fills all of space. This means that the field at larger scales can influence the field at smaller scales, and vice versa. For example, the Earth’s magnetic field can influence the motion of electrons in atoms, which can lead to the emission of photons.
• The electromagnetic field is a fundamental field of nature, and it does not require the presence of charged particles to exist. The field is always there, even if it is not being disturbed.
###### References

An electromagnetic field can be thought of as a single more complete object than its component electric and magnetic field. It propagates through space in the form of bundles of energy called photons which are configured as electromagnetic waves, the force carriers of radiant energy (electromagnetic radiation).

• An electromagnetic field results from the coupling of an electric and magnetic field.
• When an electromagnetic field experiences a change in voltage or current its reconfiguration into an electromagnetic wave can be described in terms of wavelength, frequency and energy.
• An electromagnetic wave can be thought to come into existence when a static electric field experiences a change in voltage or a static magnetic field experiences a change in current producing radiating oscillations of electromagnetic energy that propagate through space.
• The difference between an electromagnetic field and an electromagnetic wave is that the wave has a non-zero frequency component which is the source of the energy it transports.
• Electromagnetic radiation is essentially the result of an oscillating electromagnetic field propagating through space.

## Electromagnetic force

The electromagnetic force is one of the four fundamental forces in nature and is responsible for electricity, magnetism, and light. It governs the interaction between electrically charged particles, such as electrons and protons. The other forces are the strong nuclear force, the weak nuclear forces and gravity.

• The electromagnetic force is a fundamental force, its effects manifest as the push and pull interactions between charged particles.
• This means this force is not derived from anything else. It cannot be further broken down or explained by simpler forces.
• Even though the nature of the electromagnetic force is not fully understood, classical physics and quantum mechanics can provide a precise understanding of its emergence from charged particles, its behaviour, and the interactions it governs.
• It is one of the four most basic and essential forces in the universe. These four forces exist independently of each other, although they can interact and influence each other in certain situations.
##### Protons, electrons & photons
• The electromagnetic force, mediated by the exchange of photons, arises in the presence of and from the movement of electrically charged particles such as protons and electrons within atoms.
• Protons are positively charged and electrons are negatively charged. Due to the electromagnetic force like charges attract one another whilst opposite charges repel.
• This push and pull process is likely to take one of three forms:
• 1. The push and pull that holds an atom together
• The force holding an atom together is primarily the electrostatic force which is a specific aspect of the electromagnetic force.
• This force arises from the attraction between oppositely charged particles within an atom. Protons (positively charged) in the nucleus attract electrons (negatively charged) surrounding the nucleus.
• This attraction is mediated by the exchange of virtual photons. These virtual photons constantly fluctuate in the electromagnetic field and carry the influence of the force between the charged particles.
• A virtual photon is a temporary fluctuation in the electromagnetic field and cannot be directly observed.
• 2. Push and pull below the threshold of an electron transition
• This refers to the continuous, underlying force between charged particles in an atom, even when it does not produce an electron transition.
• This doesn’t involve emitting or absorbing a real photon but rather the ongoing exchange of virtual photons mediating the attraction or repulsion.
• Even when an atom is in its ground state, the electromagnetic force keeps electrons in their specific orbitals due to this continuous exchange. The force’s strength might vary depending on the distance and arrangement of charges within the atom, but real photons aren’t emitted or absorbed as long as the electrons remain in the same energy level.
• 3. Force that causes an electron transition
• This case represents a change in the existing electromagnetic force rather than a separate force.
• When an atom absorbs energy (e.g., from light), an electron can be excited to a higher energy level.
• The absorbed energy (which could be in the form of a real photon) provides the impetus for the electron to overcome the attraction from the nucleus and move to a higher energy orbital.
• No real photon is emitted during the absorption process itself.
• The emission of real photons only occurs when an electron transitions from a higher energy level to a lower one.
• In this case, the transition involves the emission of a real photon with an energy equal to the difference in energy levels between the initial and final states.
• This emission signifies the release of energy by the electron and is a consequence of the existing electromagnetic force, not a separate force itself.
##### Real photons
• Real photons are fundamental particles that carry electromagnetic force over long distances. They are massless and travel at the speed of light in a vacuum.
• Unlike virtual photons, which are temporary fluctuations in the electromagnetic field, real photons exist independently and can be detected or measured.
• The visible light we see originates from real photons emitted by various sources, such as stars, light bulbs, and even fireflies.
• The different colours of light correspond to different frequencies of these photons.
• Radio waves, microwaves, and X-rays are also examples of electromagnetic radiation consisting of real photons with different frequencies and energies.
##### Characteristics of real photons
• Quantized energy: They come in discrete packets of energy, with the energy of each photon directly proportional to its frequency.
• Electromagnetic spectrum: Different frequencies of real photons correspond to different parts of the electromagnetic spectrum, encompassing visible light, radio waves, X-rays, and more.
• Light source: Real photons are emitted by various light sources when electrons in atoms or molecules undergo transitions between energy levels. The specific energy of the emitted photon corresponds to the difference in energy levels between the initial and final states of the electron.
###### References
• The electromagnetic force is one of the four fundamental forces in nature, responsible for various phenomena including electricity, magnetism, and light. It governs the interaction between electrically charged particles, such as electrons and protons. The other forces are the strong nuclear force, the weak nuclear forces and gravity.
• The electromagnetic force is a fundamental force, its effects manifest as the push and pull interactions between charged particles.
• This means this force is not derived from anything else. It cannot be further broken down or explained by simpler forces.
• Even though the nature of the electromagnetic force is not fully understood, classical physics and quantum mechanics can provide a precise understanding of its emergence from charged particles, its behaviour, and the interactions it governs.
• It is one of the four most basic and essential forces in the universe. These four forces exist independently of each other, although they can interact and influence each other in certain situations.

## Electromagnetic force: manifestations

The electromagnetic force is a fundamental force that has many different manifestations in the natural world. The force itself cannot be directly observed in the same way that a physical object might be observed. Instead, it is understood and studied through its effects on matter and energy.

##### Electrostatic force
• The electrostatic force is the component of the electromagnetic force that acts between electrically charged particles. It is the force that holds atoms together and is responsible for the formation of molecules. It is used to generate electricity, which is used to power our homes and schools.
##### Magnetic force
• The magnetic force is the other component of the electromagnetic force, a phenomenon that arises from the motion of electric charges. It is the force that acts between magnets and moving electric charges. Magnets are objects that produce a magnetic field, which is a region of space where a force is exerted on other magnets and on moving electric charges. Magnets are used in compasses, motors, and generators.
##### Light
• Light is a form of electromagnetic radiation. Electromagnetic radiation can travel through space in the form of waves. Light is used by our eyes and is also used for communication and heating.
##### Chemical Bonding
• Chemical bonding is the force that holds atoms together to form molecules. It is caused by the attraction between the electrons in the atoms and the protons in the nucleus.
##### The Structure of Atoms and Molecules
• The electromagnetic force is responsible for the structure of atoms and molecules. The electrons in an atom are held in place by the attractive force between the negatively charged electrons and the positively charged nucleus. The bonds between atoms are also produced by the electromagnetic force, specifically the attraction between the electrons in one atom and the protons in another atom.
##### Behaviour of Matter
• The electromagnetic force affects the behaviour of matter in many ways. For example, it affects the way that matter conducts heat and electricity, the way that matter interacts with light, and the way that matter reacts with other matter.
##### Formation of Stars and Galaxies
• The electromagnetic force is involved in the formation of stars and galaxies. It is responsible for the formation of clouds of gas and dust within space, and it also plays a role in the collapse of these clouds to form stars and galaxies.

Summary

## Electromagnetic force: properties

The electromagnetic force is evident at both very small and very large scales. At one extreme, it acts between electrons and photons within atoms, which are incredibly small distances. At the macro scale, it influences how life on Earth interacts with distant cosmic events.

• The electromagnetic force acts between electrons and photons within atoms. Electrons are negatively charged particles, while photons are quanta of electromagnetic energy. The electromagnetic force mediates their interactions, enabling electrons to transition between energy levels and photons to be emitted or absorbed. The distances involved in atomic interactions are incredibly small on the order of angstroms (10^-10 meters).
• The electromagnetic force is responsible for interactions between charged particles at macroscopic scales. For example, it governs the interactions between celestial bodies and life on Earth. The distances involved in such interactions can indeed be measured in light years. Examples include:
• Human sight is enabled by the interaction of electromagnetic radiation with specialized cells in the retina of the eye called photoreceptors. These cells are sensitive to certain wavelengths of light, allowing us to perceive our surroundings. Our understanding of the world is heavily reliant on electromagnetic radiation (light), which allows us to observe and study both near and distant objects.
• Photosynthesis is a crucial process for plants, algae, and some bacteria. It involves the conversion of electromagnetic energy (sunlight) into chemical energy in the form of glucose. Without light, there would be no life on Earth.
• The properties listed below help to explain many of the phenomena associated with electromagnetic force, such as the behaviour of light, the formation of atoms and molecules, and the attraction between magnets.
• Properties of the electromagnetic force include:
• Charge: The electromagnetic force is only exerted between electrically charged particles. Particles with the same charge repel each other, while particles with opposite charges attract each other.
• Direction: The electromagnetic force is a vector force, meaning that it has both magnitude and direction. The direction of the electromagnetic force is always along the line connecting the two charged particles.
• Range: The electromagnetic force is a long-range force, meaning that it can act over large distances. However, the force between two charged particles decreases as the distance between them increases.
• Strength: The electromagnetic force is the second strongest of the four fundamental forces. The order and relative strength of fundamental forces are:
• Strong force (1)
• Electromagnetic force (1/137)
• Weak force (10-6)
• Gravity (10-37)
• Universality: The electromagnetic force is universal, meaning that it acts on all electrically charged particles in the same way, regardless of their mass or composition.
###### References

Summary

Electromagnetic radiation refers to the transfer of all forms of radiation through space by electromagnetic waves (or their quanta, photons) . This includes gamma rays, ultraviolet (UV), infrared (IR), X-rays, and radio waves, as well as visible light.

• Detached from its source, electromagnetic radiation (EM radiation or EMR), is transported by electromagnetic waves and propagates through space at the speed of light.
• Man-made technologies that produce electromagnetic radiation include radio and TV transmitters, radar, MRI scanners, microwave ovens, computer screens, mobile phones, all types of lights and lamps, electric blankets, electric bar heaters, lasers and x-ray machines.
• At the quantum scale of electromagnetism, electromagnetic radiation is described in terms of photons rather than waves. Photons are elementary particles responsible for all electromagnetic phenomena.
• The term quantum refers to the smallest quantity into which something can be divided. A quantum of a thing is indivisible into smaller units so they have no sub-structure.  A photon is a quantum of electromagnetic radiation.
• A single photon with a wavelength corresponding with gamma rays might carry 100,000 times the energy of a single photon of visible light.
• Electromagnetic radiation has both energy and momentum. The energy of electromagnetic radiation is proportional to its frequency, while the momentum of electromagnetic radiation is proportional to its wavelength.
• In the context of electromagnetic radiation, proportional means that the energy and momentum of the radiation are directly related to its frequency and wavelength.
• As a result,  if the frequency of the radiation increases, the energy and momentum of the radiation also increase. Similarly, if the wavelength of the radiation decreases, the energy and momentum of the radiation also increase.
##### Particle-wave duality
• The particle concepts, energy and momentum, and the wave concepts, frequency and wavelength, are all connected with particle-wave duality.
• Particle-wave duality is the concept that all objects have both particle-like and wave-like properties. This means that objects can behave like particles in some situations and like waves in other situations.
• Particle-wave duality can be seen in many different experiments. For example, if we shine a beam of light at a double slit, we will see an interference pattern on the screen behind the slits. This interference pattern is characteristic of waves. However, if we reduce the intensity of the light beam until only one photon is passing through the slits at a time, we will still see the interference pattern. This shows that the photon, which is a particle, is also behaving like a wave
##### Equations
• The energy and momentum of an object are related to its frequency and wavelength by the following equations:
``````E = hf
p = h/λ
``````

where:

• E is the energy of the object
• p is the momentum of the object
• h is Planck’s constant
• f is the frequency of the object’s associated wave
• λ is the wavelength of the object’s associated wave
• These equations show that the energy and momentum of an object are directly related to the frequency and wavelength of its associated wave. This means that if an object has a higher energy or momentum, it will also have a higher frequency and wavelength.
###### References

Electromagnetic radiation is a type of energy more commonly simply called light. Detached from its source, it is transported by electromagnetic waves (or their quanta, photons) and propagates through space at the speed of light.

• Electromagnetic radiation (EM radiation or EMR) includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.
• Man-made technologies that produce electromagnetic radiation include radio and TV transmitters, radar, MRI scanners, microwave ovens, computer screens, mobile phones, all types of lights and lamps, electric blankets, electric bar heaters, lasers and x-ray machines.
• At the quantum scale of electromagnetism, electromagnetic radiation is described in terms of photons rather than waves. Photons are elementary particles responsible for all electromagnetic phenomena.
• The term quantum refers to the smallest quantity into which something can be divided. A quantum of a thing is indivisible into smaller units so they have no sub-structure.  A photon is a quantum of electromagnetic radiation.
• A single photon with a wavelength corresponding with gamma rays might carry 100,000 times the energy of a single photon of visible light.

Electromagnetic radiation refers to the transfer of all forms of radiation through space by electromagnetic waves.

• Electromagnetic radiation includes gamma rays, ultraviolet (UV), infrared (IR), X-rays, and radio waves, as well as visible light.
• Detached from its source, electromagnetic radiation (EM radiation), is transported by electromagnetic waves (or their quanta, photons) and propagates through empty space at the speed of light.
• Man-made technologies that produce electromagnetic radiation include radio and TV transmitters, radar, MRI scanners, microwave ovens, computer screens, mobile phones, all types of lights and lamps, electric blankets, electric bar heaters, lasers and x-ray machines.

## Electromagnetic spectrum

The electromagnetic spectrum encompasses electromagnetic waves with every possible wavelength (and corresponding frequencies) of electromagnetic radiation, spanning low-energy radio waves through visible light to high-energy gamma rays.

• The electromagnetic spectrum is continuous, with no gaps between the different types of waves.
• There are no precisely defined boundaries between the bands of electromagnetic radiation in the electromagnetic spectrum.
• The electromagnetic spectrum includes, in order of increasing frequency: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
• The frequency of an electromagnetic wave is inversely proportional to its wavelength. This means that as the frequency increases, the wavelength decreases, and vice versa.
• Visible light constitutes only a small fraction of the entire electromagnetic spectrum.
• Each type of electromagnetic wave has distinct properties and interacts differently with matter.
• Electromagnetic waves can carry energy, momentum, and angular momentum away from their source and can impart those quantities to matter they interact with.
##### Electromagnetic Induction
• Electromagnetic waves can be generated by changing magnetic fields. When a magnetic field alters, it induces an electric field. This fluctuating electric field in turn produces a varying magnetic field, resulting in an electromagnetic wave.
##### Acceleration of Charged Particles
• When a charged particle is accelerated, it emits electromagnetic radiation. This principle is used in devices such as radio antennas and television broadcasting systems, where electrons are rapidly accelerated in metallic structures, producing radio and television waves.
##### Electronic Transitions in Atoms and Molecules
• When electrons in atoms or molecules transition between energy levels (either absorbing energy to move to a higher energy level or emitting energy to fall to a lower energy level), they emit or absorb electromagnetic waves.
##### Nuclear Transitions
• Similar to electronic transitions, nuclear transitions (changes in energy levels within atomic nuclei) also produce electromagnetic radiation, typically in the gamma-ray region of the spectrum.
##### Annihilation Processes
• When a particle and its corresponding antiparticle collide, they annihilate each other, and their rest mass is converted into electromagnetic radiation, typically in the form of gamma rays.
###### References

The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low energy radio waves through visible light to high energy gamma rays.

• There are no precisely defined boundaries between the bands of electromagnetic radiation in the electromagnetic spectrum.
• The electromagnetic spectrum includes, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
• Visible light is only a very small part of the electromagnetic spectrum.

## Electromagnetic spectrum

The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low energy radio waves through visible light to high energy gamma rays.

• There are no precisely defined boundaries between the bands of electromagnetic radiation in the electromagnetic spectrum.
• The electromagnetic spectrum includes, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
• Visible light is only a very small part of the electromagnetic spectrum.