A report on Light and Electromagnetic radiation

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
400x400px
The electromagnetic spectrum, with the visible portion highlighted
Shows the relative wavelengths of the electromagnetic waves of three different colours of light (blue, green, and red) with a distance scale in micrometers along the x-axis.
800px
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power, so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Electromagnetic radiation thus includes the far field part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, forms part of the changing electromagnetic field, but does not count as electromagnetic radiation.
Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily
Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. The electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together.
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation.
Hong Kong illuminated by colourful artificial lighting.
James Clerk Maxwell
Pierre Gassendi.
Electromagnetic spectrum with visible light highlighted
Christiaan Huygens.
Rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation
Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.
400x400px

Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye.

- Light

It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

- Electromagnetic radiation
A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.

23 related topics with Alpha

Overall
The emission of electrons from a metal plate caused by light quanta – photons.

Photoelectric effect

5 links

The emission of electrons from a metal plate caused by light quanta – photons.
Schematic of the experiment to demonstrate the photoelectric effect. Filtered, monochromatic light of a certain wavelength strikes the emitting electrode (E) inside a vacuum tube. The collector electrode (C) is biased to a voltage VC that can be set to attract the emitted electrons, when positive, or prevent any of them from reaching the collector when negative.
Diagram of the maximum kinetic energy as a function of the frequency of light on zinc.
The gold leaf electroscope to demonstrate the photoelectric effect. When the electroscope is negatively charged, there is an excess of electrons and the leaves are separated. If short wavelength, high-frequency light (such as ultraviolet light obtained from an arc lamp, or by burning magnesium, or by using an induction coil between zinc or cadmium terminals to produce sparking) shines on the cap, the electroscope discharges, and the leaves fall limp. If, however, the frequency of the light waves is below the threshold value for the cap, the leaves will not discharge, no matter how long one shines the light at the cap.
Photomultiplier
Angle-resolved photoemission spectroscopy (ARPES) experiment. Helium discharge lamp shines ultraviolet light onto the sample in ultra-high vacuum. Hemispherical electron analyzer measures the distribution of ejected electrons with respect to energy and momentum.

The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material.

Circular polarization on rubber thread, converted to linear polarization

Polarization (waves)

3 links

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Circular polarization on rubber thread, converted to linear polarization
cross linear polarized
A "vertically polarized" electromagnetic wave of wavelength λ has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B (or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z).
Electric field oscillation
100px
100px
100px
100px
100px
Animation showing four different polarization states and three orthogonal projections.
A circularly polarized wave as a sum of two linearly polarized components 90° out of phase
200px
Color pattern of a plastic box showing stress-induced birefringence when placed in between two crossed polarizers.
Paths taken by vectors in the Poincaré sphere under birefringence. The propagation modes (rotation axes) are shown with red, blue, and yellow lines, the initial vectors by thick black lines, and the paths they take by colored ellipses (which represent circles in three dimensions).
A stack of plates at Brewster's angle to a beam reflects off a fraction of the s-polarized light at each surface, leaving (after many such plates) a mainly p-polarized beam.
Stress in plastic glasses
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
Effect of a polarizer on reflection from mud flats. In the picture on the left, the horizontally oriented polarizer preferentially transmits those reflections; rotating the polarizer by 90° (right) as one would view using polarized sunglasses blocks almost all specularly reflected sunlight.
One can test whether sunglasses are polarized by looking through two pairs, with one perpendicular to the other. If both are polarized, all light will be blocked.
The effects of a polarizing filter (right image) on the sky in a photograph
Colored fringes in the Embassy Gardens Sky Pool when viewed through a polarizer, due to stress-induced birefringence in the skylight
Circular polarization through an airplane plastic window, 1989

Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids.

White light is dispersed by a prism into the colors of the visible spectrum.

Visible spectrum

3 links

Portion of the electromagnetic spectrum that is visible to the human eye.

Portion of the electromagnetic spectrum that is visible to the human eye.

White light is dispersed by a prism into the colors of the visible spectrum.
Laser beams with visible spectrum
Newton's color circle, from Opticks of 1704, showing the colors he associated with musical notes. The spectral colors from red to violet are divided by the notes of the musical scale, starting at D. The circle completes a full octave, from D to D. Newton's circle places red, at one end of the spectrum, next to violet, at the other. This reflects the fact that non-spectral purple colors are observed when red and violet light are mixed.
Newton's observation of prismatic colors (David Brewster 1855)
How visible light interacts with objects to make them colorful
Approximation of spectral colors on a display results in somewhat distorted chromaticity
Earth's atmosphere partially or totally blocks some wavelengths of electromagnetic radiation, but in visible light it is mostly transparent

Electromagnetic radiation in this range of wavelengths is called visible light or simply light.

Quantum

2 links

Minimum amount of any physical entity (physical property) involved in an interaction.

Minimum amount of any physical entity (physical property) involved in an interaction.

For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation).

Aurora at Alaska showing light created by charged particles and magnetism, fundamental concepts to electromagnetism study

Electromagnetism

3 links

Branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles.

Branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles.

Aurora at Alaska showing light created by charged particles and magnetism, fundamental concepts to electromagnetism study
Hans Christian Ørsted
André-Marie Ampère
James Clerk Maxwell
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation.
Magnetic reconnection in the solar plasma gives rise to solar flares, a complex magnetohydrodynamical phenomenon.

The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light.

Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers

Laser

3 links

Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers
A laser beam used for welding
frameless
A helium–neon laser demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the gain medium for the laser. The laser produces a tiny, intense spot on the screen to the right. The center of the spot appears white because the image is overexposed there.
Spectrum of a helium–neon laser. The actual bandwidth is much narrower than shown; the spectrum is limited by the measuring apparatus.
Lidar measurements of lunar topography made by Clementine mission.
Laserlink point to point optical wireless network
Mercury Laser Altimeter (MLA) of the MESSENGER spacecraft
Aleksandr Prokhorov
Charles H. Townes
LASER notebook: First page of the notebook wherein Gordon Gould coined the acronym LASER, and described the elements required to construct one. Manuscript text: "Some rough calculations on the feasibility / of a LASER: Light Amplification by Stimulated / Emission of Radiation. / Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.
Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).
A 50 W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range
A 5.6 mm 'closed can' commercial laser diode, such as those used in a CD or DVD player
Close-up of a table-top dye laser based on Rhodamine 6G
The free-electron laser FELIX at the FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein
Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments.
The US–Israeli Tactical High Energy weapon has been used to shoot down rockets and artillery shells.
Laser application in astronomical adaptive optics imaging

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

Fig. 1: Schematic diagram of Compton's experiment. Compton scattering occurs in the graphite target on the left. The slit passes X-ray photons scattered at a selected angle. The energy of a scattered photon is measured using Bragg scattering in the crystal on the right in conjunction with ionization chamber; the chamber could measure total energy deposited over time, not the energy of single scattered photons.

Compton scattering

4 links

Scattering of a high frequency photon after an interaction with a stationary charged particle, usually an electron.

Scattering of a high frequency photon after an interaction with a stationary charged particle, usually an electron.

Fig. 1: Schematic diagram of Compton's experiment. Compton scattering occurs in the graphite target on the left. The slit passes X-ray photons scattered at a selected angle. The energy of a scattered photon is measured using Bragg scattering in the crystal on the right in conjunction with ionization chamber; the chamber could measure total energy deposited over time, not the energy of single scattered photons.
Fig. 3: Energies of a photon at 500 keV and an electron after Compton scattering.

Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain shifts in wavelength at low intensity: classically, light of sufficient intensity for the electric field to accelerate a charged particle to a relativistic speed will cause radiation-pressure recoil and an associated Doppler shift of the scattered light, but the effect would become arbitrarily small at sufficiently low light intensities regardless of wavelength.

At energies of a few eV to a few keV, corresponding to visible light through soft X-rays, a photon can be completely absorbed and its energy can eject an electron from its host atom, a process known as the photoelectric effect.

A pendulum making 25 complete oscillations in 60 s, a frequency of 0.41 Hertz

Frequency

2 links

Number of occurrences of a repeating event per unit of time.

Number of occurrences of a repeating event per unit of time.

A pendulum making 25 complete oscillations in 60 s, a frequency of 0.41 Hertz
A pendulum with a period of 2.8 s and a frequency of 0.36 Hz
Diagram of the relationship between the different types of frequency and other wave properties.
Modern frequency counter
Complete spectrum of electromagnetic radiation with the visible portion highlighted
The sound wave spectrum, with rough guide of some applications

Frequency is an important parameter used in science and engineering to specify the temporal rate of change observed in oscillatory and periodic phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

Visible light is an electromagnetic wave, consisting of oscillating electric and magnetic fields traveling through space.

A ray of light being refracted in a plastic block.

Refraction

1 links

Redirection of a wave as it passes from one medium to another.

Redirection of a wave as it passes from one medium to another.

A ray of light being refracted in a plastic block.
Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the phase velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.
A pen partially submerged in a bowl of water appears bent due to refraction at the water surface.
When a wave moves into a slower medium the wavefronts get compressed. For the wavefronts to stay connected at the boundary the wave must change direction.
A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.
An image of the Golden Gate Bridge is refracted and bent by many differing three-dimensional drops of water.
The sun appears slightly flattened when close to the horizon due to refraction in the atmosphere.
Heat haze in the engine exhaust above a diesel locomotive.
Mirage over a hot road.
Water waves are almost parallel to the beach when they hit it because they gradually refract towards land as the water gets shallower.

Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction.

1) Light slows as it travels through a medium other than vacuum (such as air, glass or water). This is not because of scattering or absorption. Rather it is because, as an electromagnetic oscillation, light itself causes other electrically charged particles such as electrons, to oscillate. The oscillating electrons emit their own electromagnetic waves which interact with the original light. The resulting "combined" wave has wave packets that pass an observer at a slower rate. The light has effectively been slowed. When light returns to a vacuum and there are no electrons nearby, this slowing effect ends and its speed returns to c.

Emission spectrum of a metal halide lamp.

Emission spectrum

1 links

Emission spectrum of a metal halide lamp.
A demonstration of the 589 nm D2 (left) and 590 nm D1 (right) emission sodium D lines using a wick with salt water in a flame
Emission spectrum of hydrogen
Emission spectrum of iron
Schematic diagram of spontaneous emission

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an electron making a transition from a high energy state to a lower energy state.

In physics, emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in the production of light.