Electromagnetism: Concepts

The sun emits electromagnetic radiation.

Protons: Carry a positive charge. Electrons: Carry a negative charge. Quarks: Fundamental particles that carry fractional charges.

Any charged object creates an electric field around it. This field exerts a force on other charged objects within its range.

Strong Nuclear Force: Holds the nucleus of an atom together. Weak Nuclear Force: Involved in radioactive decay. Electromagnetic Force: Governs the interactions between charged particles. Gravity: The force of attraction between any two objects with mass.

Electromagnetic charge is a fundamental property of matter that determines how a particle interacts with the electromagnetic field.Charges are either positive (+) or negative (-).

A virtual photon is a theoretical concept in particle physics. Virtual photons are thought to be particles that exist for an incredibly brief time and cannot be directly observed. Their existence is inferred through their role in mediating interactions between other particles.

• Virtual photons are created when two charged particles interact with each other. For example, when two electrons interact with each other, they can exchange a virtual photon. This exchange of a virtual photon causes the electrons to repel each other. The electric force that we observe is thought to be due to the exchange of virtual photons between charged particles.
• Virtual photons are thought to play a role in many different physical phenomena, including the electromagnetic force, the weak force, and the strong force.
• More generally, a photon is a particle that carries electromagnetic radiation. It is the fundamental unit of light.

Electric charge is a fundamental property of matter that governs its interaction with electric and magnetic fields.

• Electric charge carriers, protons (+) and electrons (-) are the primary charge carriers in matter.
• There are two types of electric charge:
  • Positive charge: Carried by protons, found in the nucleus of atoms.
  • Negative charge: Carried by electrons, which exist in orbitals around the nucleus.
• Neutons, the other particles within the nucleus of an atom, have no charge.

Electromagnetism is the fundamental force that governs the behaviour of electric and magnetic fields. It encompasses the generation, interaction, and propagation of these fields as electromagnetic waves, and includes the principles and phenomena related to these interactions.

In its broadest sense, electromagnetism refers to the entire realm of phenomena arising from the fundamental electromagnetic force. This includes:

• The electromagnetic force itself: The interaction between electrically charged particles, causing attraction or repulsion.
• Electromagnetic fields: Invisible fields associated with charged particles and currents, exerting forces on other charged particles.
• Electromagnetic radiation: Energy travelling in the form of waves or particles (photons), such as light, radio waves, and X-rays.

• Find out more about electromagnetism here.

• 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.

In physics, a force is anything that can make an object move differently. It’s like a push or a pull that can make an object start moving, stop moving, or change direction. Imagine kicking a soccer ball – the kick is the force that makes the ball move.

• Forces can be either contact forces or non-contact forces.
  • Contact forces: These happen when two objects touch, like friction when you rub your hands together, or the push you give the ball.
  • Non-contact forces: These act even when objects aren’t touching, like gravity pulling you down, or a magnet attracting a paperclip.
  • Non-contact forces are forces that act between objects that are not in contact with each other. Examples of non-contact forces include gravity, electromagnetism, and the strong nuclear force.
• Forces can make things move faster (accelerate), slower (decelerate), or change direction altogether.
• Objects, bodies, matter, particles, radiation, and space-time are all in motion.
• On a cosmological-scale, concentrated matter in planets, stars, and galaxies leads to significant push-pull interactions.
• Motion signifies a change in the position of the elements of a physical system including translational motion, rotational motion, vibrational motion, and oscillatory motion.

Radiation is energy that comes from a source and travels through space at the speed of light.

• Radiant energy has an electric field, and a magnetic field and may be described in terms of electromagnetic waves or in terms of bundles of photons travelling in a wave-like pattern.
• Visible light is a form of radiation often described in terms of either electromagnetic waves or photons.
• Types of radiation with the highest energy include ultraviolet radiation, x-rays, and gamma rays.
• When x-rays or gamma-rays interact with atoms, they can remove electrons which destabilises them and make them radioactive.
• Radioactivity is the spontaneous release of energy from an unstable atom as it returns to a stable state.
• Ionizing Radiation is the energy that comes out of a radioactive atom.

An electromagnetic wave carries electromagnetic radiation.

• An electromagnetic wave describes electromagnetic radiation as it propagates from a light source, travels through space and encounters different materials.
• Electromagnetic waves can be imagined as synchronised oscillations of electric and magnetic fields that propagate at the speed of light in a vacuum.
• Electromagnetic waves are similar to other types of waves in so far as they can be measured in terms of wavelength, frequency and amplitude.
• We can feel electromagnetic waves release their energy when sunlight warms our skin.
• Remember that electromagnetic radiation can be described either as an oscillating wave or as a stream of particles, called photons, which also travel in a wave-like pattern.
• The notion of waves is often used to describe phenomena such as refraction or reflection whilst the particle analogy is used when dealing with phenomena such as diffraction and interference.

Classical electromagnetism is a theory of physics that describes the interaction of electric and magnetic fields at macroscopic scales. It was developed in the late 19th century by physicists such as James Clerk Maxwell and Michael Faraday. Classical electromagnetism precedes quantum physics.

• Classical electromagnetism is based on the idea that electric charges and electromagnetic fields are continuous and smooth. It does not take into account the quantization of energy or the wave-particle duality of matter.
• Charged particles create electromagnetic fields, which in turn exert electromagnetic forces on other charged particles.
• The four Maxwell equations are:
  • Gauss’s law for electricity: The electric flux through a closed surface is proportional to the total electric charge enclosed by the surface.
  • Gauss’s law for magnetism: There are no magnetic monopoles, and the magnetic flux through a closed surface is always zero.
  • Faraday’s law of induction: A changing magnetic field produces an electric field.
  • Ampere’s circuital law with Maxwell’s correction: A changing electric field or an electric current produces a magnetic field.
• These equations can be used to describe a wide range of phenomena, from the propagation of electromagnetic waves to the operation of electrical and electronic devices. They are also used in many different fields, including engineering, medicine, and astronomy.

A photon is a particle that carries electromagnetic radiation. It is the fundamental unit of light.

• Thinking of photons as particles is useful for understanding the quantum nature of light.
• In the world of quantum physics, photons are the fundamental constituents of all forms of electromagnetic radiation, including light. They serve as the carriers of the electromagnetic force.
• Photons are elementary particles that have no mass and no electric charge. They are the quanta of the electromagnetic field, which is the fundamental field that describes electromagnetic interactions. Electromagnetic radiation, including light, is a manifestation of the electromagnetic field.
• Photons are the carriers of electromagnetic force because they are the only particles that can mediate electromagnetic interactions. When two charged particles interact electromagnetically, they exchange photons. The exchange of photons gives rise to the electromagnetic force.<
• Photons have no rest mass and always travel at the speed of light in a vacuum.
• Photons exhibit both wave-like and particle-like properties, a characteristic referred to as wave-particle duality. This duality is inherent to quantum particles, causing light to behave as a wave under certain conditions, as both waves and photons in others, and strictly as particles in yet others.