Dictionary tag: E

• • 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.

Characteristics of Electromagnetic Waves

• An electromagnetic wave, travelling at the speed of light in a vacuum, is produced when either the voltage (charge) of an electric field changes or when the amperage (current) in a conductor changes. These changes in electric and magnetic fields result in synchronized oscillations, propagating at right angles to each other. This type of wave is often referred to as a transverse wave.
• The velocity at which electromagnetic waves propagate in a vacuum is the speed of light which is 299,792 kilometres per second.

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.

• 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.

• 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.

• 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.

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).

About Recombination

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.

• The amount of energy carried by an electromagnetic wave is directly proportional to its frequency and inversely proportional to its wavelength.
• Radio waves have the longest wavelength and lowest frequency so carry the least energy among electromagnetic waves, while gamma rays have the shortest wavelength and highest frequency in the electromagnetic spectrum and carry the most energy.
• Electromagnetic waves are composed of oscillating electric and magnetic fields that travel through space at the speed of light.

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.

• An electromagnetic field is a single more complete object than its component electric and magnetic fields.
• An electromagnetic field is created when an electric field and a magnetic field interact at right angles to each other.
• An electromagnetic field, when oscillating, can generate electromagnetic waves.
• Electromagnetic waves can be described in terms of wavelength, frequency and energy.
• Electromagnetic waves carry energy through space.
• The main distinction between an electromagnetic field and an electromagnetic wave is that the former is a more abstract concept.
  • An electromagnetic field is a region of space where electric and magnetic fields exist.
  • But these fields do not necessarily transport energy, so it is not the fields that produce light.
  • Electromagnetic waves do transport energy because their electric and magnetic fields are oscillating at non-zero frequencies.
• In the field of quantum mechanics, electromagnetic waves can be understood as packets of energy called photons.
• Photons are essentially the force carriers of electromagnetic radiation.
• The electromagnetic spectrum is a range of all possible wavelengths of electromagnetic fields in motion. It includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays, each distinguished by its specific wavelength.
• Visible light is an electromagnetic field in motion, oscillating within a range of wavelengths that our eyes perceive as colours.
• Electromagnetic radiation, an example of an electromagnetic wave, is produced by an oscillating electromagnetic field and can travel through vacuum, air, or solid materials.

• 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.

• Manifestations of the electromagnetic force can be observed in:
  • The propagation of electromagnetic radiation: radio waves, microwaves, infrared radiation, ultraviolet radiation, X-rays, and gamma rays.
  • The behaviour of light, such as reflection, refraction, and diffraction.
  • The generation of electricity.
  • The attraction and repulsion between magnets.
  • The structure of atoms and molecules.
  • The formation of chemical bonds.
• These manifestations are underpinned by the following facets of electromagnetism:

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.

• The electromagnetic force plays a crucial role in atomic interactions, but it acts through the exchange of photons, which are quanta of electromagnetic energy. Photons mediate interactions that enable electrons to transition between energy levels, leading to the emission or absorption of photons.
• At macroscopic scales, the electromagnetic force governs interactions between charged particles and has broad implications, though gravitational forces are often more significant for celestial bodies. Examples include:
• The interaction of electromagnetic radiation (light) with specialized cells in the retina called photoreceptors enables vision. These cells are sensitive to various wavelengths of light, allowing us to perceive and interpret our surroundings. Our ability to observe and study both near and distant objects relies heavily on electromagnetic radiation.
• 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.