Name: measuring light with wavelength and frequency
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 12 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

The Wave Nature of Light

La luce del sole, il forno a microonde usato per cuocere il cibo e le onde radio emesse dai router wi-fi sono tutti esempi di radiazioni elettromagnetiche. La radiazione elettromagnetica è la trasmissione dell'energia che proviene dal movimento di particelle cariche elettricamente. Questo movimento crea campi elettrici e magnetici oscillanti perpendicolari che si propagano nello spazio sotto forma di onde.

Come tutte le onde, le onde elettromagnetiche sono caratterizzate dalla loro ampiezza, lunghezza d'onda e frequenza. L'ampiezza del picco è la distanza dalla linea mediana al picco o alla depressione di un'onda. Essa determina l'intensità dell'onda.

Per esempio, l'ampiezza della luce visibile è correlata alla sua luminosità;maggiore è l'ampiezza, più luminosa o più intensa è la luce. La lunghezza d'onda è la distanza tra punti identici su onde adiacenti, come picchi o diminuzioni successive;è simboleggiato dalla lettera greca lambda. La radiazione elettromagnetica può essere classificata in base alla lunghezza d'onda, che può variare da chilometri a picometri.

Per esempio, l'intervallo di lunghezze d'onda della luce visibile è di circa 400-750 nanometri, che corrispondono rispettivamente alla luce viola e rossa. La frequenza, che è simboleggiata dalla lettera greca nu, è il numero di cicli d'onda che attraversano un punto di riferimento in un secondo e si misura in hertz, o cicli al secondo. La lunghezza d'onda è la larghezza di un ciclo.

La velocità di un'onda è il prodotto della sua frequenza e lunghezza d'onda. Dunque, la frequenza di un'onda è direttamente proporzionale alla velocità alla quale l'onda viaggia. Tuttavia, è inversamente proporzionale alla lunghezza d'onda dell'onda stessa.

Pertanto, le onde con lunghezze d'onda lunghe, come le onde radio, hanno basse frequenze. Queste onde sono meno energetiche di quelle con alte frequenze e lunghezze d'onda corte, come i raggi gamma.

la natura ondulatoria della luce

La natura della luce stata oggetto di studio fin dall’antichit. Nel diciassettesimo secolo Isaac Newton effettu esperimenti con lenti e prismi e riusc a dimostrare che la luce bianca costituita dai singoli colori dell'arcobaleno combinati insieme. Newton spieg le sue scoperte sull'ottica in termini di una visione "corpuscolare" della luce, in cui la luce era composta da flussi di particelle estremamente piccole che viaggiavano ad alta velocit secondo le leggi del movimento di Newton.

Altri nel XVII secolo, come Christiaan Huygens, avevano dimostrato che fenomeni ottici come la riflessione e la rifrazione potevano essere altrettanto ben spiegati in termini di luce come onde che viaggiano ad alta velocit attraverso un mezzo chiamato "etere luminifero" che si pensava permeasse tutto lo spazio. All’inizio del diciannovesimo secolo, Thomas Young dimostr che la luce che passa attraverso fenditure strette e ravvicinate produceva schemi di interferenza che non potevano essere spiegati in termini di particelle newtoniane ma potevano essere facilmente spiegati in termini di onde. Pi tardi, nel diciannovesimo secolo, dopo che James Clerk Maxwell svilupp la sua teoria della radiazione elettromagnetica e dimostr che la luce era la parte visibile di un vasto spettro di onde elettromagnetiche, la visione corpuscolare della luce venne completamente screditata.

Entro la fine del diciannovesimo secolo, gli scienziati consideravano l'universo fisico come composto da due domini separati: la materia composta da particelle che si muovono secondo le leggi del movimento di Newton e la radiazione elettromagnetica costituita da onde governate dalle equazioni di Maxwell. Oggi, questi domini sono indicati come meccanica classica ed elettrodinamica classica (o elettromagnetismo classico). Sebbene esistessero alcuni fenomeni fisici che non potevano essere spiegati all’interno di questo quadro, gli scienziati dell’epoca erano cos sicuri della solidit complessiva di questo quadro che consideravano queste aberrazioni come paradossi sconcertanti che alla fine sarebbero stati risolti in qualche modo all’interno di questo quadro. Questi paradossi hanno portato a un quadro contemporaneo che collega intimamente particelle e onde a un livello fondamentale chiamato dualit onda-particella, che ha sostituito la visione classica.

La luce visibile e altre forme di radiazione elettromagnetica svolgono un ruolo importante in chimica poich possono essere utilizzate per dedurre le energie degli elettroni all'interno di atomi e molecole. Gran parte della tecnologia moderna si basa sulla radiazione elettromagnetica. Ad esempio, le onde radio di un telefono cellulare, i raggi X utilizzati dai dentisti, l’energia utilizzata per cuocere il cibo nel microonde, il calore radiante di oggetti roventi e la luce dello schermo televisivo sono forme di radiazione elettromagnetica che mostrano tutte un comportamento ondulatorio.

Onde

Un'onda un'oscillazione o movimento periodico in grado di trasportare lenergia da un punto all'altro dello spazio. Esempi comuni di onde sono ovunque intorno a noi. Scuotere l'estremit di una corda trasferisce energia dalla mano all'altra estremit della corda, far cadere un sasso in uno stagno provoca onde che si increspano verso l'esterno lungo la superficie dell'acqua e l'espansione dell'aria che accompagna un fulmine genera onde sonore (il tuono) che pu viaggiare verso l'esterno per diversi chilometri. In ciascuno di questi casi, l'energia cinetica viene trasferita attraverso la materia (la corda, l'acqua o l'aria) mentre la materia rimane essenzialmente al suo posto.

Le onde non hanno bisogno di essere limitate per viaggiare attraverso la materia. Come ha dimostrato Maxwell, le onde elettromagnetiche sono costituite da un campo elettrico che oscilla di pari passo con un campo magnetico perpendicolare, entrambi perpendicolari alla direzione di viaggio. Queste onde possono viaggiare nel vuoto a una velocit costante di 2.998 108 m/s, la velocit della luce (indicata con c).

Tutte le onde, comprese le forme di radiazione elettromagnetica, sono caratterizzate da una lunghezza d'onda (indicata con λ, la lettera greca minuscola lambda), una frequenza (indicata con ν, la lettera greca minuscola nu) e un'ampiezza.

La lunghezza d'onda la distanza tra due picchi o valli consecutivi di un'onda (misurata in metri nel sistema SI). Le onde elettromagnetiche hanno lunghezze d'onda che rientrano in un intervallo enorme: sono state osservate lunghezze d'onda da chilometri (103 m) a picometri (10-12 m). La frequenza il numero di cicli d'onda che attraversano un punto specifico nello spazio in un periodo di tempo specificato (nel sistema SI, questo viene misurato in secondi). Un ciclo corrisponde ad una lunghezza d'onda completa. L'unit di frequenza, espressa in cicli al secondo [s−1], l'hertz (Hz). I multipli comuni di questa unit sono i megahertz (1 MHz = 1 106 Hz) e gigahertz (1 GHz = 1 109 Hz).

L'ampiezza corrisponde all'entit dello spostamento dell'onda, e questo corrisponde alla met dell'altezza tra i picchi e le valli. L'ampiezza legata all'intensit dell'onda, che per la luce la luminosit, e per il suono il volume. Il prodotto della lunghezza d'onda di un'onda (λ) e della sua frequenza (ν), λν, la velocit dell'onda. Pertanto, per la radiazione elettromagnetica nel vuoto, la velocit uguale alla costante fondamentale, c:

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/974/974_Equations-01.png" style="height: 40px;" />

Lunghezza d'onda e frequenza sono inversamente proporzionali: all'aumentare della lunghezza d'onda, la frequenza diminuisce. Lo spettro elettromagnetico la gamma di tutti i tipi di radiazione elettromagnetica.

La natura ondulatoria della luce

La natura della luce è stata oggetto di indagine fin dall'antichità. Nel XVII secolo, Isaac Newton eseguì esperimenti con lenti e prismi ...

Education

Didattica

JoVE Core

Chemistry

Chimica

Electronic Structure of Atoms

Struttura elettronica degli atomi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

measuring light with wavelength and frequency

Light can be described as an electromagnetic wave, and its behavior helps explain many patterns seen in science. For centuries, scientists have tried to understand light. Newton used lenses and prisms to show that white light is made of the colors of the rainbow mixed together. He explained light as tiny particles moving at high speed.

Other scientists, including Christiaan Huygens, showed that reflection and refraction could also be explained by treating light as a wave. At the time, people imagined these waves traveling through a medium called luminiferous aether, which was thought to fill all space. In the early 1800s, Thomas Young showed that light passing through two narrow slits makes an interference pattern. That result fit the wave model much better than the particle model.

James Clerk Maxwell later developed electromagnetic theory and showed that visible light is part of a much larger spectrum of electromagnetic waves. By the end of the nineteenth century, many scientists accepted a split view of the physical world. Matter was described as particles, while electromagnetic radiation was described as waves. These ideas are now called classical mechanics and classical electrodynamics, or classical electromagnetism.

Some experimental results did not fit that classical picture. Scientists first saw them as strange puzzles that might still be solved within the old framework. Those puzzles eventually led to wave-particle duality, a modern idea that links waves and particles at a basic level. This idea replaced the older view.

Electromagnetic radiation matters in chemistry because it can help reveal the energies of electrons in atoms and molecules. It also powers many technologies. Radio waves from a mobile phone, X-rays used by dentists, microwave energy used to cook food, radiant heat from red-hot objects, and the light from a television screen are all forms of electromagnetic radiation. Each of these shows wavelike behavior.

A wave is an oscillation, or repeating motion, that carries energy from one place to another. Rope waves, ripples on water after a pebble falls in, and sound waves from thunder are common examples. In these cases, energy moves through the rope, water, or air while the material itself stays mostly in place. Waves do not have to travel through matter, because electromagnetic waves can move through empty space.

Maxwell showed that electromagnetic waves contain an electric field and a magnetic field that oscillate together. These fields are perpendicular to each other and to the direction the wave travels. In a vacuum, electromagnetic waves move at 2.998 × 10^8 m/s, which is the speed of light, c. Like all waves, they are described by wavelength, frequency, and amplitude.

Wavelength is the distance between two peaks or two troughs. Frequency is the number of wave cycles that pass a point in a given time. Amplitude is the size of the wave’s displacement, which is half the height between a peak and a trough. Amplitude is related to intensity, so for light it affects brightness, and for sound it affects loudness. Wavelength and frequency are linked by the equation λν = speed, so in a vacuum c = λν. As wavelength increases, frequency decreases. Electromagnetic waves span a huge range, from kilometers to picometers, and the full set is called the electromagnetic spectrum.

Measuring Light with Wavelength and Frequency

measuring-light-with-wavelength-and-frequency

the wave nature of light

Light can be described as an electromagnetic wave, and its behavior helps explain many patterns seen in science. For centuries, scientists have tried to understand light. Newton used lenses and prisms to show that white light is made of the colors of the rainbow mixed together. He explained light as tiny particles moving at high speed. Other scientists, including Christiaan Huygens, showed that reflection and refraction could also be explained by treating light as a wave. At the time, people...

the electromagnetic spectrum

Electromagnetic Waves: Uses Across the Spectrum

The electromagnetic spectrum includes all electromagnetic radiation arranged by frequency and wavelength. Visible light is only a small part of it, and each color of visible light has its own frequency and wavelength. Different parts of the spectrum also use different units. Radio waves are usually measured in MHz, while the visible range is often measured in nm or angstroms. The spectrum is organized from radio waves to gamma rays as frequency increases and wavelength decreases. Radio waves...

interference and diffraction

Wave Patterns from Light and Slits

Light can form wave patterns through interference and diffraction. When two electromagnetic waves meet with their peaks and troughs lined up, they combine into a larger wave. This is constructive interference, and the waves are in phase. When a peak of one wave meets a trough of the other, the waves reduce each other. This is destructive interference, and the result has a much lower amplitude. Diffraction is another wave behavior. When light passes through a slit that is about the same size as...

photoelectric effect

Why Light Ejects Electrons from Metals

Light can eject electrons from a metal surface when it has the right frequency. This process is called the photoelectric effect. Each metal has its own threshold frequency, which is the minimum light frequency needed to free electrons. Light below the threshold frequency cannot cause emission, even if it is very bright. When the light frequency is above the threshold, electrons are ejected. In that case, the number of electrons released is directly proportional to the intensity, or brightness,...

the bohr model

Bohr’s Quantized Atomic Orbits

Bohr’s quantized atomic orbits explain why hydrogen atoms can stay stable. Early in the twentieth century, Ernest Rutherford and his colleagues described atoms as tiny dense nuclei with lighter electrons moving around them. This picture was called the planetary model because it compared the atom to a miniature solar system, with electrons orbiting the nucleus like planets around the sun. The simplest atom is hydrogen. It has one proton in the nucleus and one electron moving around it. In the...

emission spectra

Line Spectra from Heated Gases

Line spectra are produced when heated gases give off light at specific wavelengths. In contrast, hot solids, liquids, or condensed gases radiate excess energy as a continuous spectrum. That spectrum contains an unbroken range of wavelengths. A gas at low partial pressure can produce a line spectrum when it is excited by an electric current or heated. Fluorescent light bulbs and neon signs work in this way. Each element has its own characteristic set of lines, and molecules can also produce...

the de broglie wavelength

Electron Waves and Standing Orbits

Electron waves and standing orbits explain how tiny particles can behave like waves. Large objects in the macroscopic world, like a billiard ball on a table, follow classical physics. A ball keeps moving in a straight line unless it hits another ball or a force such as friction acts on it. It also has a well-defined position, velocity, and momentum, where momentum is mass times velocity. Waves behave differently from macroscopic particles. When waves interact, they can form interference...

the uncertainty principle

Electron Position and Momentum Limits

Heisenberg’s uncertainty principle sets a limit on how precisely we can know an electron’s position and momentum at the same time. Momentum is the motion of a particle, and the two measurements affect each other. If the momentum is known more accurately, the position becomes less certain, and the reverse is also true. Heisenberg described this limit with an equation that uses Planck’s constant. The equation shows the smallest possible uncertainty for position and momentum together. It explains...

the quantum-mechanical model of an atom

Electron Orbitals in Quantum Mechanics

Quantum mechanics explains how electrons behave in atoms using waves and probability. Erwin Schrödinger built on de Broglie’s idea that an electron in hydrogen could act like a circular standing wave instead of moving in fixed circular paths. He then derived the Schrödinger equation, which became a major step in modern atomic theory. When Schrödinger applied his equation to hydrogen-like atoms, it matched Bohr’s energy expression and the Rydberg formula for hydrogen spectra. He described...

quantum numbers

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Electron orbitals are described by quantum numbers that show where an electron is most likely to be found around the nucleus. These numbers come from the quantum mechanical model, which is based on solutions of the Schrödinger equation. They also help explain why electron energy comes in set values instead of changing smoothly. The principal quantum number, n, labels the energy level. It can be 1, 2, 3, and so on, and higher n values usually mean higher electron energy. This number also tells...

atomic orbitals

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the pauli exclusion principle

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the energies of atomic orbitals

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the aufbau principle and hund's rule

Electron Filling Order in Atomic Orbitals

Electron filling order in atomic orbitals follows the aufbau principle and Hund's rule. To write an electron configuration, we build atoms in order of atomic number. Starting with hydrogen and moving across the periods of the periodic table, one proton is added to the nucleus and one electron is placed into the correct subshell. This process describes the ground-state electron configurations of the elements. The aufbau principle comes from the German word aufbau, which means "to build up." It...

electron configuration of multielectron atoms

electron-configuration-of-multielectron-atoms

Valence Electrons and Noble Gas Shorthand

Valence electrons and noble gas shorthand help show how electrons are arranged in multielectron atoms. Sodium, the alkali metal with atomic number 11, has one more electron than neon. That extra electron goes into the lowest-energy subshell available, the 3s orbital, so sodium has the configuration 1s2 2s2 2p6 3s1. Electrons in the outermost shell, where n is highest, are called valence electrons. Electrons in the inner shells are called core electrons. Because core electrons often match a...

key terms and concepts

Explore light as an electromagnetic wave, including wavelength, frequency, amplitude, the speed of light, and examples from the electromagnetic spectrum.

Measuring Light with Wavelength and Frequency | JoVE K12

chemistry

JoVE Core: Chimica illustra concetti chiave di chimica attraverso video animazioni concise e di immediata comprensione. Inoltre, i video della sezione "scienziati in azione" mostrano procedure metodologiche realizzate da ricercatori provenienti dai migliori laboratori internazionali.

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Earth's Systems

3.3.9-12.H

Space Systems

3.3.9-12.B

Weather and Climate

3.3.9-12.E

Physical Science

Waves and Electromagnetic Radiation

3.2.9-12.X

Louisiana Student Standards for Science

Earth Science

Earth’s Place In The Universe

HS-ESS1-1

HS-ESS1-2

Earth’s Systems

HS-ESS2-4

Energy

HS-PS3-3

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Physics

Waves

Light phenomena

Tennessee Academic Standards

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Waves and Their Applications in Technologies for Information Transfer

PHYS.PS4.7

CHEM1.PS4.1

Virginia  Standards of Learning

HIgh School

ES.2

ES.2.a

Arizona Science Standards

HS+C.P1

HS+C.P1U1.2

CHEM.6

CHEM.6.C

Alabama Course of Study Science

Matter and Its Interactions

9-12.C.1.1.c

Earth's Place in the Universe

9-12.ESS.1.2

9-12.ESS.1.2.a

9-12.ESS.1.2.b

Next Generation Science Standards

HS-PS4-1

HS-PS4-3

Earth’s Place in the Universe

Florida Department of Education

SC.912.E.5

SC.912.E.5.8

SC.912.P.8

SC.912.P.8.3

SC.912.P.12

SC.912.P.12.7

PHYS.9

PHYS.9.A

PHYS.9.C

PHYS.9.D

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS4-4

P-PS3-3

P-PS4-1

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-7.

HS. Waves and Electromagnetic Radiation

HS-PS4-3.

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Lewis Structures of Molecular Compounds and Polyatomic Ions

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	Determine the ...

Bond Energies and Bond Lengths

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Model basic atomic structure and relate an element's atomic structure to its bonding, reactivity, and placement on the Periodic Table.

IPC.7.A

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Physical and Chemical Properties of Matter

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Physical Properties of Matter

A physical property is ...

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Atomic Radii and Effective Nuclear Charge

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Ionic Radii

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Ionization Energy

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Electron Affinity

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This process can be either ...

Use patterns within the Periodic Table to predict the relative physical and chemical properties of elements.

IPC.7.B

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Measuring Light with Wavelength and Frequency

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