# Magnetic field (dynamic)

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

##### Dynamic magnetic fields
• Photons are massless particles that carry electromagnetic energy. A photon is a quantum of light.
• Although photons have no mass, they do have energy and momentum.
• The dynamic magnetic fields produced by photons oscillate, meaning their strength varies between maximum and minimum values over time.
• The oscillations of magnetic and accompanying electric fields causes light to propagate as a wave.
• The frequency of the oscillation of the magnetic field and accompanying electric fields is the same as the frequency of the photon.
• Dynamic electric fields and dynamic magnetic fields are two sides of the same coin.
• A changing electric field creates a magnetic field, and a changing magnetic field creates an electric field. This is known as Faraday’s law of induction.
• This relationship between electric and magnetic fields is what allows for the transmission of electromagnetic energy, such as visible light. When a photon is in motion, it creates a dynamic electric field. This electric field, in turn, creates a dynamic magnetic field. The two fields propagate through space together, carrying the energy of the photon.
• The behaviour of electric and magnetic fields is described by Maxwell’s equations, a set of four fundamental equations that deal with electromagnetism.
##### Photon generation
• When a charged particle accelerates, it emits electromagnetic radiation composed of photons.
• Electromagnetic radiation encompasses light, radio waves, microwaves, X-rays, and gamma rays.
• For example, in an incandescent light bulb, electrons are heated to a high temperature, leading them to accelerate and emit photons of visible light.
• Electrons are the predominant type of charged particle that generates photons in light sources. They are found in numerous light sources, including the Sun, light bulbs, and even fireflies.
• The frequency of emitted photons by an electron depends on its energy level. Electrons possessing higher energy emit photons with greater frequencies.
• Photons can be generated by other means besides the acceleration of charged particles. For instance, photons can be produced through nuclear reactions and the decay of radioactive materials.
##### Photon behaviour
• As mentioned earlier, the acceleration of charged particles results in photons comprised of electric and magnetic fields.
• Both fields exhibit dynamic behaviour, meaning their strength oscillates between maximum and minimum values over time (time-varying fields), and in phase with one another. This creates an oscillating pattern.
• The oscillating wave motions of electric and magnetic fields are perpetually perpendicular to each other. If one is horizontal, the other is vertical. and magnetic fields are always at right angles to each other, so if one is horizontal then the other is vertical.
• Their wave-like motion propagates through empty space at the speed of light.
• The frequency of the electric and magnetic waves is consistently identical and is determined by the photon’s energy.
##### Deflection of electromagnetic waves
•  Once an electromagnetic wave propagates outward, it cannot be deflected by an external electric or magnetic field. Once an electromagnetic wave radiates outward, it remains unaffected by an external electric or magnetic field.
• This is because electromagnetic waves are massless particles that travel at the speed of light.
• However, some exceptions exist to this rule.
• For instance, 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, the gravitational deflection of light is minuscule such as in the presence of objects like galaxies and black holes.
##### Dynamic electric and magnetic fields
• Electric and magnetic fields of electromagnetic waves undergo changes over time.
• One common example is a radio wave.
• When a radio transmitter emits a signal, it generates an electromagnetic wave.
• On reaching a receiver, the oscillating electric and magnetic fields prompt an electrical current to flow in the antenna.
• This variation in fields enables the transmission and reception of information using electromagnetic waves.

A magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.

• Whilst an electric field is created by a change in voltage (charge), a magnetic field is created when electric current flows. The greater the current the stronger the magnetic field.
• An electromagnetic wave is the result of the interaction of an electric and magnetic field because an electric field induces a magnetic field and a magnetic field induces an electric field.
• An electromagnetic wave can be induced when either the charge of an electric field changes or when the current of a magnetic field changes or when they both change together.
• The waveform, wavelength and frequency of an electromagnetic wave result from the rapid periodic succession of transitions between the electrical and magnetic components and the forward propagation of the wave through space.
• When electric and magnetic fields come into contact to form electromagnetic waves they oscillate at right angles to one another.
• The direction of propagation of an electromagnetic wave is at right angles to the electric and magnetic fields.