Wiktor Wise
Electromagnetic waves are a form of radiation that travels through the universe. They are formed when an electric field couples with a magnetic field. These waves are self-perpetuating, with time-dependent changes in one field (electric or magnetic) producing the other. The energy of an electromagnetic wave is stored in its electric and magnetic fields, and it carries no mass but does carry energy, has momentum, and can exert pressure. Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate and can travel through air, solid objects, and even space. Examples of electromagnetic waves include visible light, radio waves, microwaves, x-rays, and gamma rays.
| Characteristics | Values |
|---|---|
| Type of wave | Electromagnetic waves |
| Nature of light | Both particle-like and wave-like properties |
| Speed | Speed of light |
| Energy | Radiant energy |
| Behaviour | Does not require a medium to propagate |
| Fields | Electric and magnetic fields are perpendicular to each other and to the direction of the wave |
| Source | Charged particles |
| Examples | Radio waves, microwaves, visible light, x-rays, gamma rays |
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What You'll Learn
Light as an electromagnetic wave
Light is a form of electromagnetic wave. It is made up of discrete packets of energy called photons, which carry momentum, have no mass, and travel at the speed of light. Light exhibits both particle-like and wave-like properties, with the method of observation influencing which of these properties are observed.
In the 1860s, Scottish physicist James Clerk Maxwell unified the fields of electricity, magnetism, and optics in a watershed theoretical treatment. He described light as a propagating wave of electric and magnetic fields, travelling at a speed equal to the known speed of light. Maxwell's wave equation showed that the speed of these waves, labelled 'c', is determined by a combination of constants in the laws of electrostatics and magnetostatics.
Heinrich Hertz, a German physicist, later applied Maxwell's theories to the production and reception of radio waves. Through his experiments with radio waves, Hertz demonstrated that the velocity of radio waves was equal to the velocity of light, thus proving that radio waves were a form of light.
Electromagnetic waves, including light waves, differ from mechanical waves in that they do not require a medium to propagate. They can travel through air, solid objects, and even the vacuum of space. This is because electromagnetic waves are formed when an electric field couples with a magnetic field, with the two fields being perpendicular to each other and to the direction of the wave.
The electromagnetic fields of light are not affected by travelling through static electric or magnetic fields in a linear medium such as a vacuum. However, interactions can occur in nonlinear media, such as some crystals, with examples including the Faraday effect and the Kerr effect.
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Radio waves
The polarization of radio waves is determined by the spin of photons, which can be in a right-hand or left-hand sense about their direction of motion. This results in different types of polarized waves, such as horizontally polarized, vertically polarized, and circularly polarized waves. The electric field of a radio wave is perpendicular to the direction of motion, while the magnetic field is perpendicular to the electric field.
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Electric and magnetic fields are perpendicular
Electromagnetic waves are formed when an electric field and a magnetic field interact. These waves are a form of radiation that travels through the universe and can be naturally or artificially generated. They are used in everyday technologies such as radio, wireless networks, and microwave ovens.
The electric and magnetic fields in an electromagnetic wave are perpendicular to each other and to the direction of the wave. This is due to the orthogonality of the fields, which follows directly from Maxwell's equations. James Clerk Maxwell derived a wave form of the electric and magnetic equations, revealing their wave-like nature and symmetry. He also concluded that light is a type of electromagnetic wave.
The cyclic nature of electromagnetic waves, where an electric field begets a perpendicular magnetic field, and vice versa, was first proposed by Faraday. Maxwell later developed a mathematical theory to describe this experimentally observed phenomenon. According to Maxwell's equations, the electric and magnetic fields in an electromagnetic wave have a fixed ratio of strengths and are in phase.
The perpendicular relationship between the fields is also explained by classical physics. In an electromagnetic wave, the electrical portion drives the magnetic portion at a 90-degree angle, and the magnetic portion creates the electrical portion. This interaction at 90-degree angles is known as the right-hand rule in physics.
It is important to note that the perpendicular relationship between electric and magnetic fields is not always true in all cases. In certain media, such as crystals, the electric and magnetic fields may not be perpendicular.
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Maxwell's equations
Electromagnetic waves are formed when an electric field couples with a magnetic field. These waves exhibit both particle-like and wave-like properties. Light, electromagnetic waves, and radiation all refer to the same physical phenomenon: electromagnetic energy.
The four Maxwell's equations are:
- Faraday's Law of Induction
- Ampère's circuital law
- Gauss's law
- Gauss's law for magnetism
The equations provide a mathematical model for electric, optical, and radio technologies, such as power generation, electric motors, wireless communication, lenses, and radar. They established that some charges and currents produce local electromagnetic fields near them that do not radiate.
The term "Maxwell's equations" is also used for equivalent alternative formulations, such as versions based on electric and magnetic scalar potentials, which are useful for solving the equations as a boundary value problem or in quantum mechanics. The modern form of the equations in their most common formulation is credited to Oliver Heaviside, who developed the vector calculus formalism.
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Charged particles create electromagnetic waves
Electromagnetic waves are created by the movement of charged particles. Charged particles, such as electrons and protons, create electromagnetic fields when they move, and these fields transport electromagnetic radiation or light. This radiation is a form of energy called radiant energy.
The movement of charged particles produces changing electric and magnetic fields, which are linked; a changing magnetic field will induce a changing electric field and vice versa. These changing fields form electromagnetic waves.
The energy in electromagnetic waves can be described by frequency, wavelength, or energy. All three are mathematically related, so knowing one will allow you to calculate the other two. For example, radio and microwaves are described in terms of frequency (Hertz), while infrared and visible light are described in terms of wavelength (meters).
Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. They can travel through air, solid materials, and even the vacuum of space. This is because electromagnetic waves are formed when an electric field couples with a magnetic field, and these fields can move together without a medium.
Electromagnetic waves have crests and troughs similar to ocean waves, and their energy increases as their wavelength shortens. The speed of any electromagnetic wave in free space is the speed of light.
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Frequently asked questions
Electromagnetic waves are a form of radiation that travels through the universe. They are formed when an electric field couples with a magnetic field. These waves can travel through air, solid objects, and even space, as they do not require a medium to propagate. Examples of electromagnetic waves include light, radio waves, microwaves, x-rays, and gamma rays.
Electromagnetic waves are created when charged particles, such as electrons and protons, move and create electromagnetic fields. These fields then transport electromagnetic radiation, which we know as light or photons. The energy of the wave is stored in the electric and magnetic fields, and the wave travels at the speed of light.
Electromagnetic waves are very useful for a variety of technologies. For example, when you listen to the radio, connect to a wireless network, cook with a microwave, or use a refrigerator magnet, you are utilising electromagnetic waves.
