chapter 24

Chapter 24Chapter 24

Wave OpticsWave Optics

InterferenceInterference

Light waves interfere with each Light waves interfere with each other much like mechanical waves other much like mechanical waves dodo

All interference associated with All interference associated with light waves arises when the light waves arises when the electromagnetic fields that electromagnetic fields that constitute the individual waves constitute the individual waves combinecombine

Conditions for InterferenceConditions for Interference

For sustained interference between For sustained interference between two sources of light to be observed, two sources of light to be observed, there are two conditions which there are two conditions which must be metmust be met The sources must be The sources must be coherentcoherent

They must maintain a constant phase with They must maintain a constant phase with respect to each otherrespect to each other

The waves must have identical The waves must have identical wavelengthswavelengths

Producing Coherent Producing Coherent SourcesSources

Light from a monochromatic source is Light from a monochromatic source is allowed to pass through a narrow slitallowed to pass through a narrow slit

The light from the single slit is allowed The light from the single slit is allowed to fall on a screen containing two to fall on a screen containing two narrow slitsnarrow slits

The first slit is needed to insure the light The first slit is needed to insure the light comes from a tiny region of the source comes from a tiny region of the source which is coherentwhich is coherent

Old methodOld method

Producing Coherent Producing Coherent Sources, contSources, cont

Currently, it is much more common Currently, it is much more common to use a laser as a coherent sourceto use a laser as a coherent source

The laser produces an intense, The laser produces an intense, coherent, monochromatic beam coherent, monochromatic beam over a width of several millimetersover a width of several millimeters

Young’s Double Slit Young’s Double Slit ExperimentExperiment

Thomas Young first demonstrated Thomas Young first demonstrated interference in light waves from two interference in light waves from two sources in 1801sources in 1801

Light is incident on a screen with a Light is incident on a screen with a narrow slit, Snarrow slit, Soo

The light waves emerging from this The light waves emerging from this slit arrive at a second screen that slit arrive at a second screen that contains two narrow, parallel slits, contains two narrow, parallel slits, SS11 and S and S22

Young’s Double Slit Young’s Double Slit Experiment, DiagramExperiment, Diagram

The narrow slits, SThe narrow slits, S11 and Sand S2 2 act as act as sources of wavessources of waves

The waves The waves emerging from the emerging from the slits originate from slits originate from the same wave the same wave front and therefore front and therefore are always in phaseare always in phase

Resulting Interference Resulting Interference PatternPattern

The light from the two slits form a The light from the two slits form a visible pattern on a screenvisible pattern on a screen

The pattern consists of a series of bright The pattern consists of a series of bright and dark parallel bands called and dark parallel bands called fringesfringes

Constructive interferenceConstructive interference occurs where occurs where a bright fringe occursa bright fringe occurs

Destructive interferenceDestructive interference results in a results in a dark fringedark fringe

Interference PatternsInterference Patterns

Constructive Constructive interference interference occurs at the occurs at the center pointcenter point

The two waves The two waves travel the same travel the same distancedistance Therefore, they Therefore, they

arrive in phasearrive in phase

Interference Patterns, 2Interference Patterns, 2 The upper wave has The upper wave has

to travel farther to travel farther than the lower wavethan the lower wave

The upper wave The upper wave travels one travels one wavelength fartherwavelength farther Therefore, the waves Therefore, the waves

arrive in phasearrive in phase A bright fringe A bright fringe

occursoccurs

Interference Patterns, 3Interference Patterns, 3

The upper wave The upper wave travels one-half of a travels one-half of a wavelength farther wavelength farther than the lower wavethan the lower wave

The trough of the The trough of the bottom wave bottom wave overlaps the crest of overlaps the crest of the upper wavethe upper wave

This is destructive This is destructive interferenceinterference A dark fringe occursA dark fringe occurs

Interference EquationsInterference Equations

The path The path difference, difference, δ, is δ, is found from the tan found from the tan triangletriangle

δ = rδ = r22 – r – r11 = d sin θ = d sin θ This assumes the This assumes the

paths are parallelpaths are parallel Not exactly, but a Not exactly, but a

very good very good approximationapproximation

Interference Equations, 2Interference Equations, 2

For a bright fringe, produced by For a bright fringe, produced by constructive interference, the path constructive interference, the path difference must be either zero or some difference must be either zero or some integral multiple of of the wavelengthintegral multiple of of the wavelength

δ = d sin θδ = d sin θbrightbright = m λ = m λ m = 0, ±1, ±2, … m = 0, ±1, ±2, … m is called the m is called the order numberorder number

When m = 0, it is the zeroth order maximumWhen m = 0, it is the zeroth order maximum When m = ±1, it is called the first order maximumWhen m = ±1, it is called the first order maximum


When destructive interference When destructive interference occurs, a dark fringe is observedoccurs, a dark fringe is observed

This needs a path difference of an This needs a path difference of an odd half wavelengthodd half wavelength

δ = d sin θδ = d sin θdarkdark = (m + ½) λ = (m + ½) λ m = 0, ±1, ±2, … m = 0, ±1, ±2, …


The positions of the fringes can be The positions of the fringes can be measured vertically from the zeroth measured vertically from the zeroth order maximumorder maximum

y = L tan y = L tan θ ~ θ ~ L sin L sin θθ AssumptionsAssumptions

L>>dL>>d d>>λd>>λ

ApproximationApproximation θ is small and therefore the approximation θ is small and therefore the approximation

tan tan θ ~ θ ~ sin sin θ can be usedθ can be used

Interference Equations, Interference Equations, finalfinal

For bright fringesFor bright fringes

For dark fringesFor dark fringes

2,1,0mmd

Lybright

2,1,0m2

1m

d

Lydark

Uses for Young’s Double Uses for Young’s Double Slit ExperimentSlit Experiment

Young’s Double Slit Experiment Young’s Double Slit Experiment provides a method for measuring provides a method for measuring wavelength of the lightwavelength of the light

This experiment gave the wave This experiment gave the wave model of light a great deal of model of light a great deal of credibilitycredibility It is inconceivable that particles of It is inconceivable that particles of

light could cancel each otherlight could cancel each other

Lloyd’s MirrorLloyd’s Mirror An arrangement for An arrangement for

producing an producing an interference pattern interference pattern with a single light with a single light sourcesource

Wave reach point P Wave reach point P either by a direct either by a direct path or by reflectionpath or by reflection

The reflected ray can The reflected ray can be treated as a ray be treated as a ray from the source S’ from the source S’ behind the mirrorbehind the mirror

Interference Pattern from Interference Pattern from the Lloyd’s Mirrorthe Lloyd’s Mirror

An interference pattern is formed An interference pattern is formed The positions of the dark and The positions of the dark and

bright fringes are bright fringes are reversedreversed relative relative to pattern of two real sourcesto pattern of two real sources

This is because there is a 180° This is because there is a 180° phase change produced by the phase change produced by the reflectionreflection

Phase Changes Due To Phase Changes Due To ReflectionReflection

An electromagnetic An electromagnetic wave undergoes a wave undergoes a phase change of phase change of 180° upon reflection 180° upon reflection from a medium of from a medium of higher index of higher index of refraction than the refraction than the one in which it was one in which it was travelingtraveling Analogous to a Analogous to a

reflected pulse on a reflected pulse on a stringstring

Phase Changes Due To Phase Changes Due To Reflection, contReflection, cont

There is no phase There is no phase change when the change when the wave is reflected wave is reflected from a boundary from a boundary leading to a leading to a medium of lower medium of lower index of refractionindex of refraction Analogous to a Analogous to a

pulse in a string pulse in a string reflecting from a reflecting from a free supportfree support

Interference in Thin FilmsInterference in Thin Films

Interference effects are Interference effects are commonly observed in thin filmscommonly observed in thin films Examples are soap bubbles and oil Examples are soap bubbles and oil

on wateron water Assume the light rays are Assume the light rays are

traveling in air nearly normal to traveling in air nearly normal to the two surfaces of the filmthe two surfaces of the film

Interference in Thin Films, Interference in Thin Films, 22

Rules to rememberRules to remember An electromagnetic wave traveling from a An electromagnetic wave traveling from a

medium of index of refraction nmedium of index of refraction n11 toward a toward a medium of index of refraction nmedium of index of refraction n22 undergoes a undergoes a 180° phase change on reflection when n180° phase change on reflection when n22 > n > n11

There is no phase change in the reflected wave if nThere is no phase change in the reflected wave if n22 < n< n11

The wavelength of light The wavelength of light λλnn in a medium with in a medium with index of refraction n is λindex of refraction n is λnn = λ/n where λ is the = λ/n where λ is the wavelength of light in vacuumwavelength of light in vacuum


Ray 1 undergoes a Ray 1 undergoes a phase change of phase change of 180° with respect 180° with respect to the incident rayto the incident ray

Ray 2, which is Ray 2, which is reflected from the reflected from the lower surface, lower surface, undergoes no undergoes no phase change with phase change with respect to the respect to the incident waveincident wave


Ray 2 also travels an additional Ray 2 also travels an additional distance of 2t before the waves distance of 2t before the waves recombinerecombine

For constructive interferenceFor constructive interference 2nt = (m + ½ ) 2nt = (m + ½ ) λλ m = 0, 1, 2 … m = 0, 1, 2 …

This takes into account both the difference in This takes into account both the difference in optical path length for the two rays and the optical path length for the two rays and the 180° phase change180° phase change

For destruction interferenceFor destruction interference 2 n t = m 2 n t = m λλ m = 0, 1, 2 … m = 0, 1, 2 …


Two factors influence interferenceTwo factors influence interference Possible phase reversals on reflectionPossible phase reversals on reflection Differences in travel distanceDifferences in travel distance

The conditions are valid if the medium The conditions are valid if the medium above the top surface is the same as the above the top surface is the same as the medium below the bottom surfacemedium below the bottom surface

If the thin film is between two different If the thin film is between two different media, one of lower index than the film and media, one of lower index than the film and one of higher index, the conditions for one of higher index, the conditions for constructive and destructive interference constructive and destructive interference are are reversedreversed

Interference in Thin Films, Interference in Thin Films, finalfinal

An example of An example of different indices different indices of refractionof refraction

A coating on a A coating on a solar cellsolar cell

Newton’s RingsNewton’s Rings Another method for viewing interference is to Another method for viewing interference is to

place a planoconvex lens on top of a flat glass place a planoconvex lens on top of a flat glass surfacesurface

The air film between the glass surfaces varies The air film between the glass surfaces varies in thickness from zero at the point of contact to in thickness from zero at the point of contact to some thickness tsome thickness t

A pattern of light and dark rings is observedA pattern of light and dark rings is observed This rings are called This rings are called Newton’s RingsNewton’s Rings The particle model of light could not explain the The particle model of light could not explain the

origin of the ringsorigin of the rings Newton’s Rings can be used to test optical Newton’s Rings can be used to test optical

lenseslenses

Problem Solving Strategy Problem Solving Strategy with Thin Films, 1with Thin Films, 1

Identify the thin film causing the Identify the thin film causing the interferenceinterference

The type of interference – The type of interference – constructive or destructive – that constructive or destructive – that occurs is determined by the phase occurs is determined by the phase relationship between the upper relationship between the upper and lower surfacesand lower surfaces

Problem Solving with Thin Problem Solving with Thin Films, 2Films, 2

Phase differences have two causesPhase differences have two causes differences in the distances traveleddifferences in the distances traveled phase changes occurring on reflectionphase changes occurring on reflection Both must be considered when determining Both must be considered when determining

constructive or destructive interferenceconstructive or destructive interference The interference is constructive if the path The interference is constructive if the path

difference is an integral multiple of difference is an integral multiple of λ and λ and destructive if the path difference is an odd destructive if the path difference is an odd half multiple of λhalf multiple of λ The conditions are reversed if one of the waves The conditions are reversed if one of the waves

undergoes a phase change on reflectionundergoes a phase change on reflection

CD’s and DVD’sCD’s and DVD’s

Data is stored digitallyData is stored digitally A series of ones and zeros read by laser light A series of ones and zeros read by laser light

reflected from the diskreflected from the disk Strong reflections correspond to Strong reflections correspond to

constructive interferenceconstructive interference These reflections are chosen to represent These reflections are chosen to represent

zeroszeros Weak reflections correspond to Weak reflections correspond to

destructive interferencedestructive interference These reflections are chosen to represent onesThese reflections are chosen to represent ones

CD’s and Thin Film CD’s and Thin Film InterferenceInterference

A CD has multiple tracks A CD has multiple tracks The tracks consist of a sequence of The tracks consist of a sequence of

pits of varying length formed in a pits of varying length formed in a reflecting information layerreflecting information layer

The pits appear as bumps to the The pits appear as bumps to the laser beamlaser beam The laser beam shines on the metallic The laser beam shines on the metallic

layer through a clear plastic coatinglayer through a clear plastic coating

Reading a CDReading a CD As the disk rotates, the As the disk rotates, the

laser reflects off the laser reflects off the sequence of bumps and sequence of bumps and lower areas into a lower areas into a photodectorphotodector The photodector converts The photodector converts

the fluctuating reflected the fluctuating reflected light intensity into an light intensity into an electrical string of zeros electrical string of zeros and onesand ones

The pit depth is made The pit depth is made equal to one-quarter of equal to one-quarter of the wavelength of the the wavelength of the lightlight

Reading a CD, contReading a CD, cont

When the laser beam hits a rising or When the laser beam hits a rising or falling bump edge, part of the beam falling bump edge, part of the beam reflects from the top of the bump and reflects from the top of the bump and part from the lower adjacent areapart from the lower adjacent area This ensures destructive interference and This ensures destructive interference and

very low intensity when the reflected beams very low intensity when the reflected beams combine at the detectorcombine at the detector

The bump edges are read as onesThe bump edges are read as ones The flat bump tops and intervening flat The flat bump tops and intervening flat

plains are read as zerosplains are read as zeros

DVD’sDVD’s

DVD’s use shorter wavelength DVD’s use shorter wavelength laserslasers The track separation, pit depth and The track separation, pit depth and

minimum pit length are all smallerminimum pit length are all smaller Therefore, the DVD can store about Therefore, the DVD can store about

30 times more information than a CD30 times more information than a CD

DiffractionDiffraction Huygen’s principle Huygen’s principle

requires that the requires that the waves spread out after waves spread out after they pass through slitsthey pass through slits

This spreading out of This spreading out of light from its initial line light from its initial line of travel is called of travel is called diffractiondiffraction In general, diffraction In general, diffraction

occurs when wave pass occurs when wave pass through small openings, through small openings, around obstacles or by around obstacles or by sharp edgessharp edges

Diffraction, 2Diffraction, 2

A single slit placed between a distant A single slit placed between a distant light source and a screen produces a light source and a screen produces a diffraction patterndiffraction pattern It will have a broad, intense central bandIt will have a broad, intense central band The central band will be flanked by a The central band will be flanked by a

series of narrower, less intense series of narrower, less intense secondary bandssecondary bands

Called secondary maximaCalled secondary maxima The central band will also be flanked by The central band will also be flanked by

a series of dark bandsa series of dark bands Called minimaCalled minima

Diffraction, 3Diffraction, 3

The results of the single slit cannot The results of the single slit cannot be explained by geometric opticsbe explained by geometric optics Geometric optics would say that light Geometric optics would say that light

rays traveling in straight lines should rays traveling in straight lines should cast a sharp image of the slit on the cast a sharp image of the slit on the screenscreen

Fraunhofer DiffractionFraunhofer Diffraction Fraunhofer DiffractionFraunhofer Diffraction

occurs when the rays occurs when the rays leave the diffracting leave the diffracting object in parallel object in parallel directionsdirections Screen very far from the Screen very far from the

slitslit Converging lens (shown)Converging lens (shown)

A bright fringe is seen A bright fringe is seen along the axis (along the axis (θ = 0) θ = 0) with alternating bright with alternating bright and dark fringes on and dark fringes on each sideeach side

Single Slit DiffractionSingle Slit Diffraction According to Huygen’s According to Huygen’s

principle, each portion principle, each portion of the slit acts as a of the slit acts as a source of wavessource of waves

The light from one The light from one portion of the slit can portion of the slit can interfere with light interfere with light from another portionfrom another portion

The resultant intensity The resultant intensity on the screen on the screen depends on the depends on the direction direction θθ

Single Slit Diffraction, 2Single Slit Diffraction, 2 All the waves that originate at the slit are in All the waves that originate at the slit are in

phasephase Wave 1 travels farther than wave 3 by an Wave 1 travels farther than wave 3 by an

amount equal to the path difference (a/2) sin amount equal to the path difference (a/2) sin θ θ

If this path difference is exactly half of a If this path difference is exactly half of a wavelength, the two waves cancel each other wavelength, the two waves cancel each other and destructive interference resultsand destructive interference results

In general, In general, destructive interferencedestructive interference occurs for occurs for a single slit of width a when sin a single slit of width a when sin θθdarkdark = mλ / a = mλ / a m = m = 1, 1, 2, 2, 3, …3, …

Single Slit Diffraction, 3Single Slit Diffraction, 3 The general features of The general features of

the intensity distribution the intensity distribution are shownare shown

A broad central bright A broad central bright fringe is flanked by fringe is flanked by much weaker bright much weaker bright fringes alternating with fringes alternating with dark fringesdark fringes

The points of The points of constructive interference constructive interference lie approximately lie approximately halfway between the halfway between the dark fringesdark fringes

QUICK QUIZ 24.1

In a single-slit diffraction experiment, as the width of the slit is made smaller, the width of the central maximum of the diffraction pattern becomes (a) smaller, (b) larger, or (c) remains the same.

QUICK QUIZ 24.1 ANSWER

(b). The outer edges of the central maximum occur where sin θ = ± λ/a. Thus, as a, the width of the slit, becomes smaller, the width of the central maximum will increase.

Diffraction GratingDiffraction Grating

The diffracting grating consists of The diffracting grating consists of many equally spaced parallel slitsmany equally spaced parallel slits A typical grating contains several A typical grating contains several

thousand lines per centimeterthousand lines per centimeter The intensity of the pattern on the The intensity of the pattern on the

screen is the result of the screen is the result of the combined effects of interference combined effects of interference and diffractionand diffraction

Diffraction Grating, contDiffraction Grating, cont The condition for The condition for

maximamaxima is is d sin d sin θθbrightbright = m λ = m λ

m = 0, 1, 2, …m = 0, 1, 2, … The integer m is the The integer m is the

order numberorder number of the of the diffraction patterndiffraction pattern

If the incident radiation If the incident radiation contains several contains several wavelengths, each wavelengths, each wavelength deviates wavelength deviates through a specific through a specific angleangle

Diffraction Grating, finalDiffraction Grating, final All the wavelengths are All the wavelengths are

focused at m = 0focused at m = 0 This is called the zeroth This is called the zeroth

order maximumorder maximum The first order maximum The first order maximum

corresponds to m = 1corresponds to m = 1 Note the sharpness of Note the sharpness of

the principle maxima and the principle maxima and the broad range of the the broad range of the dark areadark area This is in contrast to to This is in contrast to to

the broad, bright fringes the broad, bright fringes characteristic of the two-characteristic of the two-slit interference patternslit interference pattern

QUICK QUIZ 24.2If laser light is reflected from a phonograph record or a compact disc, a diffraction pattern appears. This occurs because both devices contain parallel tracks of information that act as a reflection diffraction grating. Which device, record or compact disc, results in diffraction maxima that are farther apart?

QUICK QUIZ 24.2 ANSWER

The compact disc. The tracks of information on a compact disc are much closer together than on a phonograph record. As a result, the diffraction maxima from the compact disc will be farther apart than those from the record.

Diffraction Grating in CD Diffraction Grating in CD TrackingTracking

A diffraction grating A diffraction grating can be used in a three-can be used in a three-beam method to keep beam method to keep the beam on a CD on the beam on a CD on tracktrack

The central maximum The central maximum of the diffraction of the diffraction pattern is used to read pattern is used to read the information on the the information on the CDCD

The two first-order The two first-order maxima are used for maxima are used for steeringsteering

Polarization of Light Polarization of Light WavesWaves

Each atom produces Each atom produces a wave with its own a wave with its own orientation of Eorientation of E

All directions of the All directions of the electric field E vector electric field E vector are equally possible are equally possible and lie in a plane and lie in a plane perpendicular to the perpendicular to the direction of direction of propagationpropagation

This is an unpolarized This is an unpolarized wavewave

Polarization of Light, contPolarization of Light, cont A wave is said to be A wave is said to be linearly linearly

polarizedpolarized if the resultant if the resultant electric field vibrates in the electric field vibrates in the same direction at all times same direction at all times at a particular pointat a particular point

Polarization can be obtained Polarization can be obtained from an unpolarized beam from an unpolarized beam by by selective absorptionselective absorption reflectionreflection scatteringscattering

Polarization by Selective Polarization by Selective AbsorptionAbsorption

The most common technique for polarizing lightThe most common technique for polarizing light Uses a material that transmits waves whose Uses a material that transmits waves whose

electric field vectors in the plane parallel to a electric field vectors in the plane parallel to a certain direction and absorbs waves whose certain direction and absorbs waves whose electric field vectors are perpendicular to that electric field vectors are perpendicular to that directiondirection

Selective Absorption, contSelective Absorption, cont

E. H. Land discovered a material E. H. Land discovered a material that polarizes light through that polarizes light through selective absorptionselective absorption He called the material He called the material polaroidpolaroid The molecules readily absorb light The molecules readily absorb light

whose electric field vector is parallel to whose electric field vector is parallel to their lengths and transmit light whose their lengths and transmit light whose electric field vector is perpendicular to electric field vector is perpendicular to their lengthstheir lengths

Selective Absorption, finalSelective Absorption, final

The intensity of the polarized beam The intensity of the polarized beam transmitted through the second transmitted through the second polarizing sheet (the analyzer) varies polarizing sheet (the analyzer) varies asas I = II = Ioo cos cos22 θθ

IIoo is the intensity of the polarized wave is the intensity of the polarized wave incident on the analyzerincident on the analyzer

This is known as This is known as Malus’ LawMalus’ Law and applies to any and applies to any two polarizing materials whose transmission two polarizing materials whose transmission axes are at an angle of axes are at an angle of θ to each otherθ to each other

Polarization by ReflectionPolarization by Reflection When an unpolarized light beam is reflected When an unpolarized light beam is reflected

from a surface, the reflected light isfrom a surface, the reflected light is Completely polarizedCompletely polarized Partially polarizedPartially polarized UnpolarizedUnpolarized

It depends on the angle of incidenceIt depends on the angle of incidence If the angle is 0° or 90°, the reflected beam is If the angle is 0° or 90°, the reflected beam is

unpolarizedunpolarized For angles between this, there is some degree of For angles between this, there is some degree of

polarizationpolarization For one particular angle, the beam is completely For one particular angle, the beam is completely

polarizedpolarized

Polarization by Reflection, Polarization by Reflection, contcont

The angle of incidence for which the The angle of incidence for which the reflected beam is completely polarized is reflected beam is completely polarized is called the called the polarizing anglepolarizing angle, , θθpp

Brewster’s Law relates the polarizing Brewster’s Law relates the polarizing angle to the index of refraction for the angle to the index of refraction for the materialmaterial

θθpp may also be called Brewster’s Angle may also be called Brewster’s Angle

pp

p tancos

sinn

Polarization by ScatteringPolarization by Scattering

When light is incident on a system When light is incident on a system of particles, the electrons in the of particles, the electrons in the medium can absorb and reradiate medium can absorb and reradiate part of the lightpart of the light This process is called This process is called scatteringscattering

An example of scattering is the An example of scattering is the sunlight reaching an observer on sunlight reaching an observer on the earth becoming polarizedthe earth becoming polarized

Polarization by Scattering, Polarization by Scattering, contcont

The horizontal part of The horizontal part of the electric field the electric field vector in the incident vector in the incident wave causes the wave causes the charges to vibrate charges to vibrate horizontallyhorizontally

The vertical part of the The vertical part of the vector simultaneously vector simultaneously causes them to causes them to vibrate verticallyvibrate vertically

Horizontally and Horizontally and vertically polarized vertically polarized waves are emittedwaves are emitted

Optical ActivityOptical Activity

Certain materials display the Certain materials display the property of property of optical activityoptical activity A substance is optically active if it A substance is optically active if it

rotates the plane of polarization of rotates the plane of polarization of transmitted lighttransmitted light

Optical activity occurs in a material Optical activity occurs in a material because of an asymmetry in the because of an asymmetry in the shape of its constituent materialsshape of its constituent materials

Liquid CrystalsLiquid Crystals A A liquid crystalliquid crystal is a substance with properties is a substance with properties

intermediate between those of a crystalline intermediate between those of a crystalline solid and those of a liquidsolid and those of a liquid The molecules of the substance are more orderly The molecules of the substance are more orderly

than those of a liquid but less than those in a than those of a liquid but less than those in a pure crystalline solidpure crystalline solid

To create a display, the liquid crystal is To create a display, the liquid crystal is placed between two glass plates and placed between two glass plates and electrical contacts are made to the liquid electrical contacts are made to the liquid crystalcrystal A voltage is applied across any segment in the A voltage is applied across any segment in the

display and that segment turns ondisplay and that segment turns on

Liquid Crystals, contLiquid Crystals, cont

Rotation of a polarized light beam by a liquid Rotation of a polarized light beam by a liquid crystal when the applied voltage is zerocrystal when the applied voltage is zero

Light passes through the polarizer on the Light passes through the polarizer on the right and is reflected back to the observer, right and is reflected back to the observer, who sees the segment as being brightwho sees the segment as being bright

Liquid Crystals, finalLiquid Crystals, final

When a voltage is applied, the liquid crystal does When a voltage is applied, the liquid crystal does not rotate the plane of polarizationnot rotate the plane of polarization

The light is absorbed by the polarizer on the right The light is absorbed by the polarizer on the right and none is reflected back to the observerand none is reflected back to the observer

The segment is darkThe segment is dark

chapter 24

Documents