Name: wave patterns from light and slits
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 18 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Physics

Waves

Wave properties

Interference and Diffraction

Unikalną właściwością fal jest to, że kiedy wchodzą ze sobą w kontakt, oddziałują w taki sposób, że wynikowa fala ma albo zwiększoną, albo zmniejszoną amplitudę. Zjawisko to nazywa się interferencją. 

Kiedy grzbiety dwóch fal są wyrównane, są one "w fazie". Gdy fale te oddziałują ze sobą, ich amplitudy sumują się i powstaje fala o zwiększonej amplitudzie. To jest konstruktywna ingerencja. 

Jeśli dwie fale nie są wyrównane – tak, że ich grzbiety znajdują się w przeciwnych kierunkach  – są "poza fazą". W tym przypadku wynikowa fala ma mniejszą amplitudę. To jest destrukcyjna ingerencja. Kiedy dolina jednej fali całkowicie pokrywa się z grzbietem drugiej, fale znoszą się nawzajem.

Dyfrakcja to kolejne charakterystyczne zachowanie fal. Spójrz z góry na falę – tak, aby grzbiety były reprezentowane przez pionowe linie – i wyobraź sobie, że porusza się ona w kierunku bariery o wąskim otworze. Otwór w barierze ma rozmiar podobny do długości fali. 

Gdy fala przechodzi, wygina się w rogach otworu i rozchodzi się w różnych kierunkach. 

Ale jak zachowują się fale, gdy w barierze znajdują się dwa lub więcej otworów? Można to zaobserwować za pomocą źródła światła. Kiedy emitowane jest światło, fala przechodzi przez parę blisko rozmieszczonych szczelin i wyłaniają się dwie fale dyfrakcyjne. Fale te interferują ze sobą, tworząc wzór.

Kiedy dwie fale pokonują tę samą odległość, zakłócają się konstruktywnie. Obserwuje się to po pojawieniu się jasnej linii. 

W niewielkiej odległości od środka, w dowolnym kierunku, jedna fala pokonuje nieco większą odległość niż druga fala i stają się one "poza fazą". Destrukcyjna interferencja tworzy ciemny obszar. 

W zależności od odległości pokonywanych przez fale, tworzy się wzór interferencyjny naprzemiennie jasnych i ciemnych linii. Ten eksperyment z podwójną szczeliną demonstruje falową naturę światła.

interferencja i dyfrakcja

Interferencja jest zjawiskiem charakterystycznym dla fal. Kiedy dwie fale elektromagnetyczne oddziałują ze sobą, a ich szczyty i doliny pokrywają się, powstaje fala o zwiększonej amplitudzie. Nazywa się to konstruktywną interferencją. W tym przypadku dwie fale oddziałujące na siebie są w tej samej fazie.

Alternatywnie, jeśli dwie fale zbiegają się i oddziałują w taki sposób, że dolina jednej fali pokrywa się ze szczytem drugiej (w sposób przesunięty w fazie), powstała fala będzie miała znacznie niższą amplitudę. Nazywa się to destrukcyjną interferencją.

Fale wykazują również charakterystyczne zachowanie zwane dyfrakcją. Kiedy wiązka światła przechodzi przez szczelinę o wielkości porównywalnej z długością fali padającej wiązki - wiązka załamuje się (lub ugina) wokół szczeliny. I odwrotnie, gdy strumień cząstek przechodzi przez szczelinę, cząstki po prostu wychodzą przez otwór.

Ponadto, gdy wiązka światła przechodzi przez parę blisko rozmieszczonych szczelin oddzielonych odległością porównywalną z długością fali światła, w procesie dyfrakcji na każdej szczelinie powstają fale kołowe. Te dwie fale interferują ze sobą w taki sposób, że na ekranie umieszczonym w niewielkiej odległości za szczelinami uzyskuje się wzór interferencyjny z naprzemiennymi ciemnymi i jasnymi liniami.

Jasna linia powstaje na środku ekranu, gdy dwie fale pokonują równą odległość, aby dotrzeć do tego punktu i konstruktywnie interferować. Kiedy dwie fale przemieszczają się na niewielką odległość od środka w dowolnym kierunku, pokonują nieco inne odległości. Są poza fazą. Kiedy różnica w przebytych odległościach wynosi dokładnie połowę długości fali, spotykają się, wytwarzając niszczycielską interferencję. Ciemne obszary odpowiadają obszarom, w których szczyty fali z jednej szczeliny pokrywają się z dolinami fali z drugiej szczeliny (interferencja destrukcyjna), podczas gdy najjaśniejsze obszary odpowiadają obszarom, w których szczyty obu fal (lub ich dwa doliny) tak się składa, że pokrywają się (konstruktywna interferencja). Wzór dyfrakcyjny jest nieodłączną właściwością fal i stanowi przekonujący dowód na falową naturę światła.

Interferencja i dyfrakcja

Interferencja jest charakterystycznym zjawiskiem przejawianym przez fale. Kiedy dwie fale elektromagnetyczne oddziałują ze swoimi szczytami i dołkami, ...

Education

JoVE Core

Chemistry

Chemia

Jeden

Electronic Structure of Atoms

Budowa elektronowa atomów

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

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 its wavelength, it bends around the opening. A stream of particles passing through a slit does not spread in the same way and simply passes through the aperture. This contrast helps show that light behaves like a wave in this setting.

Diffraction also appears when light passes through two closely spaced slits. Each slit produces circular waves by diffraction. The two waves then interfere and form a pattern of bright and dark lines on a screen behind the slits. The center of the screen is bright because the waves travel the same distance and combine constructively. Farther from the center, the waves travel slightly different distances and become out of phase. When that path difference is one half of a wavelength, destructive interference creates dark bands. The bright and dark regions in this pattern are evidence for the wave nature of light.

Wave Patterns from Light and Slits

the wave nature of light

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...

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

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

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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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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

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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

See how light creates bright and dark bands through interference and diffraction, and how slit size and wave spacing reveal light’s wave nature.

Wave Patterns from Light and Slits | JoVE K12

chemistry

JoVE Core Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

Light phenomena

Tennessee Academic Standards

High School

waves-and-their-applications-in-technologies-for-information-transfer

Waves and Their Applications in Technologies for Information Transfer

PHYS.PS4.7

Florida Department of Education

Physical Science

SC.912.P.8

SC.912.P.8.3

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-7.

Kinetic and Potential Energy of a Wave

All forms of waves carry energy; this is directly visualized in nature. For instance, the waves of earthquakes are so intense that they can shake huge ...

Energy and Power of a Wave

The total energy associated with a wavelength is the sum of the potential energy and the kinetic energy. The average rate of energy transfer associated ...

Interference and Superposition of Waves

When two waves of the same nature occur in the same region simultaneously, they result in interference. Interference of waves implies that the net effect ...

Reflection of Waves

When a wave travels from one medium to another, it gets reflected at the boundary of the second medium. A common example of this is when a person yells at ...

Propagation of Waves

When a wave propagates from one medium to another, part of it may get reflected in the first medium, and part of it may get transmitted to the second ...

Standing Waves

Sometimes waves do not seem to move; rather, they just vibrate in place. Unmoving waves can be seen on the surface of a glass of milk kept in a ...

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Modes of Standing Waves - I

A close look at earthquakes provides evidence for the conditions appropriate for resonance, standing waves, and constructive and destructive interference. ...

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Modes of Standing Waves: II

The starting point for expressing the modes of standing waves is understanding the boundary conditions that the waves must follow. The boundary conditions ...

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Sound Waves: Interference

Sound waves can be modeled either as longitudinal waves, wherein the molecules of the medium oscillate around an equilibrium position, or as pressure ...

Interference: Path Lengths

Consider two sources of sound, that may or may not be in phase, emitting waves at a single frequency, and consider the frequencies to be the same.
Two ...

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Sound Waves: Resonance

Resonance is produced depending on the boundary conditions imposed on a wave. Resonance can be produced in a string under tension with symmetrical ...

Interference is a characteristic phenomenon exhibited by waves. When two electromagnetic waves interact with their peaks and troughs coinciding, a ...

Wave properties
• Conservation of energy
• Reflection
• Refraction
• Interference
• Diffraction

Content elaboration: When a wave reaches a barrier or a new medium, a portion of its energy is reflected at the boundary and a portion of the energy passes into the new medium. Some of the energy that passes to the new medium may be absorbed by the medium and transformed to other forms of energy, usually thermal energy, and some continues as a wave in the new medium. Some of the energy may also be dissipated and no longer be part of the wave since it has been transformed into thermal energy or transferred out of the system due to the interaction of the system with surrounding objects. Usually all of these processes occur simultaneously, but the total amount of energy must remain constant. When waves bounce off barriers (reflection), the angle at which a wave approaches the barrier (angle of incidence) equals the angle at which the wave reflects off the barrier (angle of reflection). When a wave travels from a two-dimensional (e.g., surface water, seismic waves) or three-dimensional (e.g., sound, electromagnetic waves) medium into another medium in which the wave travels at a different speed, both the speed and the wavelength of the transferred wave change. Depending on the angle between the wave and the boundary, the direction of the wave can also change, resulting in refraction. The amount of bending of waves around barriers or small openings (diffraction) increases with decreasing wavelength. When the wavelength is smaller than the obstacle or opening, no noticeable diffraction occurs. Standing waves and interference patterns between two sources are included in this topic. As waves pass through a single or double slit, diffraction patterns are created with alternating lines of constructive and destructive interference. The diffraction patterns demonstrate predictable changes as the width of the slit(s), spacing between the slits and/or the wavelength of waves passing through the slits changes.

Photoelectric Effect

When light of a particular wavelength strikes a metal surface, electrons are emitted. This is called the photoelectric effect. The minimum frequency of ...

Electromagnetic Waves

James Clerk Maxwell formulated a single theory combining all the electric and magnetic effects scientists knew during that time, calling the phenomena his ...

The Electromagnetic Spectrum

Electromagnetic waves are categorized according to their wavelengths and frequencies, giving the electromagnetic spectrum. These waves are classified as ...

The Wave Nature of Light

The nature of light has been a subject of inquiry since antiquity. In the seventeenth century, Isaac Newton performed experiments with lenses and prisms ...

dual-nature-of-electromagnetic-em-radiation

Dual Nature of Electromagnetic (EM) Radiation

Electromagnetic (EM) radiation consists of electric and magnetic field components oscillating in planes perpendicular to each other and mutually ...

Light phenomena
• Ray diagrams (propagation of light)
• Law of reflection (equal angles)
• Snell's law
• Diffraction patterns
• Wave-particle duality of light
• Visible spectrum of color

Content elaboration: The path of light waves can be represented with ray diagrams to show reflection and refraction through converging lenses, diverging lenses and plane mirrors. Since light is a wave, the law of reflection applies. Snell's law, $n_{1}sin\theta_{1}=n_{2}sin~\theta_{2},$ quantifies refraction in which n is the index of refraction of the medium and is the angle the wave enters or leaves the medium as measured from the normal line. The index of refraction of a material can be calculated by the equation $n=c/v$, where n is the index of refraction of a material, v is the speed of light through the material, and c is the speed of light in a vacuum. Diffraction patterns of light are addressed, including patterns from diffraction gratings. There are two models of how radiant energy travels through space at the speed of light. One model is that the radiation travels in discrete packets of energy called photons that are continuously emitted from an object in all directions. The energy of these photons is directly proportional to the frequency of the electromagnetic radiation. This particle-like model is called the photon model of light energy transfer. A second model is that radiant energy travels like a wave that spreads out in all directions from a source. This wave-like model is called the electromagnetic wave model of light energy transfer. Strong scientific evidence supports both the particle-like model and wave-like model. Depending on the problem scientists are trying to solve, either the particle-like model or the wave-like model of radiant energy transfer is used. Students are not required to know the details of the evidence that supports either model at this level. Humans can only perceive a very narrow portion of the electromagnetic spectrum. Radiant energy from the sun or a light bulb filament is a mixture of all the colors of light (visible light spectrum). The different colors correspond to different radiant energies. When white light hits an object, the pigments in the object reflect one or more colors in all directions and absorb the other colors.

Wave Patterns from Light and Slits

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