NV6028 New

Fresnel Biprism SetupNV6028

Operating ManualVer 1.1

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Nvis Technologies Pvt. Ltd. 2

Fresnel Biprism Setup

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Table of Contents

1. Introduction 3

2. Features 4

3. Technical Specifications 5

4. Theory 6

5. Experiments

· Experiment 1 22Determination of wavelength of monochromatic light with thehelp of Fresnel Biprism.

· Experiment 2 26Determination of fringe width by interference pattern

6. Warranty 29

7. List of Accessories 29

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IntroductionNV6028 Fresnel Biprism Setup illustrates about the phenomena of interference oflight. Interference is the interaction of two or more waves passing through the samepoint. With the help of interference phenomena we can find the wavelength ofmonochromatic light source like Laser, Sodium lamp etc. in a very simple manner.

In this experiment students understand the concept of interference, image formation,and the width of fringes. In addition, we use convex lens here to converge the imageas well as concave to diverge the fringes, which are produced by interferencephenomenon.

Young successfully demonstrated the phenomenon of interference. As Young'sDouble Slit Experiment, Double Slit Interference consists of allowing a plane wave topass through two narrow slits spaced at a certain distance apart and observing theintensity distribution given by interference between two parts of the wavefront on ascreen, placed at a certain distance away from the slits. But it was doubted that thefringes are not due to interference of light waves but due to some modification of lightwaves at the slits. These doubts were removed by Fresnel’s Biprism Experiment.

The interference of two coherent light sources occurs when waves of equal amplitude,wavelength and velocity meet. They produce and an interference pattern, consisting ofa succession of bright and dark fringes called intensity “minima” and “maxima”. Thedark fringe corresponds to destructive interference, while the bright fringes are due toconstructive interference.

By using Biprism, Fresnel obtained two coherent sources from a single source ofrefraction.

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Features

· A comprehensive and self contained optics system

· A complete system with a light source, bench and all other accessories

· Sliding uprights are provided

· Laser as a monochromatic source is provided

· Convex lens is provided for focused image

· Concave lens for clear vision of fringes

· Two years warranty

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Optics Bench

Technical Specifications

Length : 1.5 m

Laser Source

Wavelength : 630 nm

Output : Less than 3mW

Biprism

Dimension : 50 x 40 mm

Material : Glass

Refractive Index : 1.54

Convex Lens

Type : Double Convex

Focal Length : 100 mm

Diameter : 50mm

Concave Lens

Type : Double Concave

Focal Length : 200 mm

Diameter : 75mm

Screen

Horizontal Scale : 100-0-100 mm

Vertical Scale : 85-0-85 mm

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Theory

Optics is the branch of science which describes the behaviour and properties of lightand the interaction of light with matter. Optics explains the optical phenomena.Thefield of optics usually describes the behavior of visible, infrared, and ultraviolet light;however because light is an electromagnetic wave. Geometrical optics deals with theproperties of reflection and refraction of light, as part of the study of mirrors, lenses,and optical fibers.

Wave :

A wave is a disturbance that propagates through space and time, usually with transferof energy. While a mechanical wave exists in a medium (which on deformation iscapable of producing elastic restoring forces), waves of electromagnetic radiation(and probably gravitational radiation) can travel through vacuum, that is, without amedium. Waves travel and transfer energy from one point to another, often with littleor no permanent displacement of the particles of the medium (that is, with little or noassociated mass transport); instead there are oscillations around almost fixedpositions.

Periodic waves are characterized by crests (highs) and troughs (lows), and mayusually be categorized as either longitudinal or transverse. Transverse waves are thosewith vibrations perpendicular to the direction of the propagation of the wave;examples include waves on a string and electromagnetic waves. Longitudinal wavesare those with vibrations parallel to the direction of the propagation of the wave;examples mostly include most sound waves.

Waves can be described using a number of standard variables including: frequency,wavelength, amplitude and period.

All waves have common behaviour under a number of standard situations. All wavescan experience the following:

Reflection : Waves direction change from hitting a reflective surface.

Refraction : Waves direction change from entering a new medium.

Diffraction : Bending of waves as they interact with obstacles in their path,most pronounced for wavelengths on the order of the diffracting object size.

Interference : Superposition of two waves that come into contact with eachother (collide).

Dispersion : Wave splitting up by frequency.

Rectilinear propagation : The movement of light waves in a straight line.

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Wavelength :

The wavelength is the distance between two corresponding points in the wave'spattern (e.g. normally two peaks or two valleys, but can be any other correspondingpoints) in some quantity, usually an intensity. It is commonly designated by the greekletter lambda (λ).There are two types of wavelength that are excitation and emissionwavelength. The excitation wavelength is the wavelength of the radiation (usuallycoming from a laser line) used to stimulate fluorescence in the measured object. Thestimulated dye will emit radiation with a particular emission wavelength.

Frequency and Time Period :

Figure 1

The period (T) is the time for one complete cycle for an oscillation of a wave. Thefrequency (f) is how many periods per unit time (for example one second) and ismeasured in hertz.

These are related by:

f = 1/T

Frequency is cycles per second. A cycle in a wave is from one point to the same pointas in from crest to crest. Another way to express frequency is:

f = c / λ

When waves are expressed mathematically, the angular frequency (ω, radians/second)is often used; it is related to the frequency f by:

f = ω / 2π

All electromagnetic waves travel at the speed of light in vacuum. (Other waves suchas sound waves travel at much lower velocities), and electromagnetic waves travel ata speed lower than speed of light in non-vacuum medium. Different types ofelectromagnetic waves have different frequencies.

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Amplitude :

The amplitude or peak amplitude of a wave is a measure of oscillation. Amplitudesare always positive numbers (for example: 3.5, 1, 120) and are never negative (forexample: -3.5, -1, -120). Amplitudes are positive because distance can only be greaterthan zero or equal to zero; negative distance does not exist.

The distance from the top of one peak to the bottom of another is called peak-to-peakamplitude. Or we can say that peak to peak amplitude is the distance between themaximum positive value and the maximum negative value of a wave.

Speed :

Speed of wave is the distance that wave moves in a certain amount of time. Speed is ameasure of how fast wave is moving. Speed is a scalar quantity. When speed changes(the wave starts moving faster), it is called acceleration. Decreasing speed is calleddeceleration, or negative acceleration.

Basic Optics Property :

Reflection :

When light is incident on any surface and it returns back to the same medium, thisphenomena is known as Reflection.

If a ray of light could be observed approaching and reflecting off a flat mirror, thenthe behaviour of the light as it reflects would follow a predictable law known as theLaw of Reflection. The figure 2 below illustrates the law of reflection.

Figure 2

In the figure 2, the ray of light approaching the mirror is known as the Incident Ray(labeled I in the figure 2). The ray of light which leaves the mirror is known as theReflected Ray (labeled R in the figure 2). At the point of incidence where the raystrikes the mirror, a line can be drawn perpendicular to the surface of the mirror. Thisline is known as a Normal line (labeled N in the figure 2). The normal line divides theangle between the incident ray and the reflected ray into two equal angles. The anglebetween the incident ray and the normal is known as the Angle of Incidence. Theangle between the reflected ray and the normal is known as the Angle of Reflection.

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Refraction :

Refraction is the name given to the observed phenomenon that light changes thedirection, or "bends," as it passes the boundary between one medium and another.

Figure 3Here, we see a beam of light traveling through air, until it meets a surface of glass. Itarrives at some angle to the surface as shown in figure 3. As it passes through theboundary, going from air to glass, it actually slows down.

If we change the angle at which the light enters the glass, we find that the angle of thelight in the glass also changes, as we change the entering angle more and more awayfrom the perpendicular, we see that the ray of light in the glass bends more and moreaway from the direction taken by that ray of light in the air.

Diffraction :

Diffraction is the phenomena associated with the bending of waves, when theyinteract with obstacles in their path. It occurs with any type of wave, including soundwaves, water waves, and electromagnetic waves such as visible light, X-rays andradio waves. As physical objects have wave-like properties, diffraction also occurswith matter and can be studied according to the principles of quantum mechanics.While diffraction always occurs when propagating waves encounter obstacles in theirpaths, its effects are generally most pronounced for waves where the wavelength is onthe order of the size of the diffracting objects. The complex patterns resulting fromthe intensity of a diffracted wave are a result of interference between different parts ofa wave that traveled to the observer by different paths.

Figure 4

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Polarization :

A light wave which is vibrating in more than one plane is referred to as unpolarizedlight. Light emitted by the sun, by a lamp in the classroom, or by a candle flame isunpolarized light. Such light waves are created by electric charges which vibrate in avariety of directions, thus creating an electromagnetic wave which vibrates in avariety of directions. This concept of unpolarized light is rather difficult to visualize.It is possible to transform unpolarized light into polarized light. Polarized light wavesare light waves in which the vibrations occur in a single plane. The process oftransforming unpolarized light into polarized light is known as polarization.

Polarization is a property of transverse waves which describes the orientation of theoscillations in the plane perpendicular to the wave's direction of travel. Longitudinalwaves such as sound waves in liquids and gases do not exhibit polarization, becausefor these waves the direction of oscillation is along the direction of wave's travel. Incontrast, the direction of the (electric field) oscillation in electromagnetic waves is notuniquely determined by the direction of propagation. Polarization is present in therainbow, in the hidden colour of minerals, in the dance of honeybees, in the flow ofmolten metal, in the colour of beetles, and the gloss of tree leaves at dawn etc.

Interference :

Interference is the phenomenon which occurs when two waves meet while travelingalong the same medium. It works on the principle of superposition. The source shouldbe coherent, monochromatic having same wavelength and same velocity.

Constructive interference is a type of interference which occurs at any location alongthe medium where the two interfering waves have a displacement in the samedirection.

Destructive interference is a type of interference which occurs at any location alongthe medium where the two interfering waves have a displacement in the oppositedirection.

Figure 5

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Monochromatic light source :

Monochromatic light can be described by only one frequency light of a singlewavelength or very narrow bandwidth. Monochromatic light is made up of a singlecolour of light.

A monochromatic light is an optical device that transmits a mechanically selectablenarrow band of wavelengths of light or other radiation chosen from a wider range ofwavelengths available at the input. The name is from the Greek roots, mono-meanssingle, and chroma means colour.

If we see the figure given below figure 6 shows, the comparision between white lightsource and monochromatic light source and in which laser light source is the bestexample of monochromatic light source.

Figure 6

A device that can produce monochromatic light has many uses in science and inoptics because many optical characteristics of a material are dependent on colour.Although there are a number of useful ways to produce pure colours, there are not somany other ways to easily select any pure colour in a wide range.

Prism :

A prism is a transparent optical element with flat, polished surfaces that refract light.The exact angles between the surfaces depend on the application. The traditionalgeometrical shape is that of a triangular prism with a triangular base and rectangularsides, and in colloquial use "prism" usually refers to this type. Some types of opticalprism are not in fact in the shape of geometric prisms. Prisms are typically made outof glass, but can be made from any material that is transparent to the wavelengths forwhich they are designed. A prism can be used to break light up into its constituentspectral colours (the colours of the rainbow). Prisms can also be used to reflect light,or to split light into components with different polarizations.

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Figure 7

Light changes speed as it moves from one medium to another (for example, from airinto the glass of the prism). This speed-change causes light striking the boundarybetween two media at an angle to be refracted and enter the new medium at a differentangle (Huygens principle), or to be reflected away from it. The amount of reflectedlight and the degree of bending of the light's path will depend on the angle that theincident beam of light makes with the surface, and on the ratio between the refractiveindices of the two media (Snell's law).

Types of prisms :

1. Dispersive prisms : Dispersive prisms are used to break up light into itsconstituent spectral colours because the refractive index depends on frequency;the white light entering the prism is a mixture of different frequencies, each ofwhich bends slightly differently.

2. Reflective prisms : Reflective prisms are used to reflect light, for instance inbinoculars.

3. Polarizing prisms : There are also polarizing prisms which can split a beam oflight into components of varying polarization. These are typically made of abirefringent crystalline material.

4. Fresnel biprism : Fresnel Biprism consists of a glass prism, two faces of whichmake an angle of nearly 180o with one another, and are equally inclined to thethird face making the other two angles each equal to 30”.

There are also many other types of prism.

Fresnel Biprism

Figure 8

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Uses of Prism :

Prisms are used to reflect light, for instance in binoculars, since they are easier tomanufacture than mirrors. Prisms can also be used to break up light into itsconstituent spectral colours because the refractive index depends on frequency; thewhite light entering the prism is a mixture of different frequencies, each of which getsbends slightly differently. Blue light is slowed down more than red light and willtherefore be bent more than red light.

Lens

A piece of a transparent material, such as glass, with two polished surfaces – oneconcave or convex, and the other plane, concave, or convex – that modifies rays oflight. The way to distinguish among the two types of lenses is to look at the relativethickness of two parts, the center and the edges. Converging lenses are thicker in themiddle than they are at the edges, while diverging lenses are thicker at the edges thanthey are in the middle.

A convex lens brings rays of light together; a concave lens makes the rays diverge.Here convex lens is used to converge the images of source and concave lens used todiverge the fringes to count easily.

· Convex lens :

It is a converging lens thick in the middle and thin at the edges. If both the surfacesare convex, it is called a double convex or a bi-convex lens. If one surface is convexand the other plane is called plano-convex lens. If one surface is concave and theother is convex is called concavo-convex lens.

· Concave lens

Figure 9

It is a diverging lens thin in the middle and thick at the edges. If both the surfaces areconcave, it is called a double concave or a bi-concave lens. If one surface is concaveand the other plane is called plano-concave lens. If one surface is convex and theother concave is called convexo-concave lens.

Figure 10

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Interference and its types :Interference is the addition (superposition) of two or more waves that results in a newwave pattern.

As most commonly used, the term interference usually refers to the interaction ofwaves which are correlated or coherent with each other, either because they comefrom the same source or because they have the same or nearly the same frequency.

Two non-monochromatic waves are only fully coherent with each other if they bothhave exactly the same range of wavelengths and the same phase differences at each ofthe constituent wavelengths.

It is based on the principle of superposition and this principle works when two ormore waves pass simultaneously through the same region. When two sinusoidalwaves of the same wavelength and amplitude travel in the same direction, thisprinciple works there.

The nature of the interference pattern produced by two bobbing sources is shown infigure 11. The diagram at the right depicts the pattern resulting from the propagationof water waves across the surface of the water. The waves propagate outward fromthe point sources, forming a series of concentric circles about the source. In thediagram, the thick lines represent wave crests and the thin lines represent wavetroughs. The crests and troughs from the two sources interfere with each other at aregular rate to produce nodes (shown in dark circle in the diagram) and antinodes(shown in light circle) along the water surface. The nodal positions are locationswhere the water is undisturbed; the antinodal positions are locations where the wateris undergoing maximum disturbances above and below the surrounding water level.One unique feature of the two-point source interference pattern is that the antinodaland nodal positions all lie along distinct lines. Each line can be described as arelatively straight hyperbola. The spatial separation between the antinodal and nodallines in the pattern is related to the wavelength of the waves.

Figure 11· If the waves are exactly in phase so that the peaks and valleys of one are exactly

aligned with those of the other, they combine to double the displacement ofeither wave.

· If they are exactly out of phase they combine to cancel everywhere and theytravel straight.

This phenomenon of combining waves is called interference and the waves are said tointerfere.

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Conditions for Interference :

1. The light should be monochromatic. (Light of a single wavelength or a narrowwavelength range).

2. The two sources, which are producing interference, must be coherent. (The lightwaves of same frequency or wavelength and of a stable phase difference).

3. The waves, which are causing interference, must be of same wavelengths andmust travel with same velocity.

4. To observe interference pattern clearly, it is necessary that fringe width ω issufficiently large. They should be observing at sufficiently large distance.

The interference of two coherent light sources occurs when waves of equal amplitudemeet. They produce interference pattern, consisting of a succession of bright and darkfringes called intensity “minima” and “maxima”. The dark fringes correspond todestructive interference, while the bright fringes are due to constructive interference.

In Young’s Double Slit Experiment, light travels through a narrow slit and undergoesdiffraction. This causes the light to spread out and enter two narrow slits. These slitsin theory behave as point sources and light coming from them interferes, to produce apattern of bright and dark fringes.

Types of interference :

There are two types of interference Constructive and Destructive Interference.

Light waves from the same source that are traveling in direction D, as illustratedbelow in figure 12. If the vibrations, which are perpendicular to the propagationdirection as represented by C, are parallel to each other and are parallel with respect tothe direction of vibration, then the light waves may interfere with each other.However, if the vibrations are not in the same plane or are vibrating at 90 degrees toeach other, then they cannot interfere with one another. Then the waves can interfereeither constructively or destructively with each other.

· Constructive interference :

If the crests of one wave coincide with the crests of the other, the amplitudes of thewaves are additive. Thus, if the amplitudes of both waves are equal, the resultantamplitude is doubled. It is important to remember, however, that light intensity variesdirectly as the square of the amplitude. Thus, if the amplitude of a light wave isdoubled, its intensity is quadrupled. Such additive interference is demonstrated infigure 12 and is known as Constructive Interference.

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Figure 12

When the two light wave’s travels have the phase difference is the even integralmultiple of or the path difference is the integral multiple of λ.

x = n λ

Where, x is path difference and n = 0, 1, 2 …etc.

· Destructive Interference :

If the crests of one wave coincide with the troughs of the other wave, the resultantamplitude is decreased, as illustrated in figure 13. This destructive interference isaccompanied by a decrease in light intensity and may even result in completeblackness if a total cancellation of light waves occurs.

Figure 13

When the two light wave’s travels have the phase difference is an odd integralmultiple of or the path difference is the odd integral multiple of λ/2.

x = (2n + 1) λ/2

Where, x is path difference and n = 0, 1, 2 …etc.

Whenever light constructively interferes (such as when a crest meeting a crest or atrough meeting a trough), the two waves act to reinforce one another and to produce a"super light wave." On the other hand, whenever light destructively interferes (such aswhen a crest meets a trough), the two waves act to destroy each other and produce nolight wave. Thus, the two-point source interference pattern would still consist of an

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alternating pattern of antinodal lines and nodal lines. However for light waves, theantinodal lines are equivalent to bright lines and the nodal lines are equivalent to darklines. If such an interference pattern could be created by two light sources andprojected onto a screen, then there ought to be an alternating pattern of dark andbright bands on the screen. Since the central line in such a pattern is an antinodal line,the central band on the screen ought to be a bright band.

A two point source interference pattern creates an alternating pattern of brightand dark lines

Young Double Slit Experiment :

Figure 14

The double slit interference of electrons was crucial to the modern understanding ofwave-particle duality, while the original experiments were significant in thedevelopment of the wave model of light. This phenomenon of the particle theory oflight is revealed by an innovative physicist named Thomas Young. In 1801, heconducted an important experiment, often termed the Double-Slit Experiment, whichdemonstrated interference in such a way that it could only be explained if visible lightpossessed wave-like properties.

Figure 15

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In his experiment, Young created a coherent light source by diffracting sunlightthrough a single slit. However, in figure 15, in which the basic set-up of the double-slit experiment is illustrated, a coherent red laser acts as the light source. In thisexample, coherent laser light illuminates a barrier containing two small apertures anda screen is placed in the region behind the slits. As the light is diffracted through theapertures, each diffracted wave meets the other in a series of steps, or phases. Whenthe waves meet in step, their amplitudes add together due to constructive interferenceand a bright area is displayed on the screen. In areas where the waves meetcompletely out of step, they subtract from each other due to destructive interferenceand a dark area appears in that portion of the screen. The resulting patterns on thescreen, a product of interference between the two diffracted beams of laser light, areoften referred to as interference fringes.

The results of Young’s Double Slit Experiment quite clearly indicate interference andthe wave nature of light, when the experiment was first done objections were raisedthat the results were not conclusive since there could have been diffraction effectsfrom the edge of the slits. To counter this, Augustin Fresnel proposed a series ofinterference experiments that would have no diffracting edges. The most notable ofthese is the Fresnel biprism, where two virtual sources are created by refractionthrough a biprism.

Interference through Fresnel Biprism :

Fresnel Biprism as the name suggests consist of two prisms joined together to form anisosceles triangle. Light from the slit incident on prism and is refracted through eachhalf of the prism. This light then interferes with itself to produce an interferencepattern like Young’s slits. In Fresnel biprism there are two point sources with virtualslits. These slits are created virtually from where the light appears to come after, it isrefracted through the slit.

Fresnel Biprism :

Fresnel’s Biprism is made by joining two thin prisms at their base to create a singletriangular shape. It consists of two prisms joined to form an isosceles triangle. Lightfrom single slit S forms spherical wave’s incident on the biprism and is refractedthrough each half of the prism. These light gives interference pattern like Young’sslits.

Due to the fact that point sources are idealizations this is never the case and unwanteddiffraction effects can occur. The Fresnel biprism overcomes this by replacing the twopoint sources with virtual slits. These slits are created virtually where the light appearsto come from after is refracted through the slit. These virtual slits do behave as pointsources S1 and S2. And thus no unwanted effects occur.

Figure 16

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Advantages of Biprism :Biprism is very useful in many technologies some examples are one category oftechnique called single-lens stereovision attracted many researchers interest becauseof its significant advantages over the normal stereovision setup includingcompactness, low cost, less system parameters and ease of calibration, etc. but withthe biprism this present some new understanding of a single-lens stereovision systemusing a biprism (2F filter). Image captured by the real camera with a biprism placedbefore its lens, is divided into two equal halves. Each half-image is assumed to becaptured by one virtual camera. Two related but different approaches ofunderstanding and modeling such a system are introduced one is based on cameracalibration technique and another is based on geometrical analysis. The latter approachprovides an interesting way of understanding this system. A system of electroninterferometry and holography using two electron biprisms has been developed. Thefirst biprism is installed in the image plane of the objective lens and the second one isset behind the first magnifying lens, inside the shadow area of the first biprism. Thesystem can independently control two important parameters for interferograms andholograms, the fringe spacing and interference width. Thus, it gives us moreflexibility on performing electron interferometry and holography.

In the figure 17, the point a is the refraction edge of biprism by which we get twoimages i.e., b and c, now two waves of same wavelength and amplitude travelingthrough the same region in same direction then principle of superposition works hereand interfere alternate bright and dark fringes are produced.

Interference band with Biprism :

Figure 17

When a source S is placed parallel to the refracting edge of a biprism, it gives usvirtual images as S1 and S2, a certain distance d apart. The two sources S1 and S2 givenout light waves parallel to each other in the same phase having same amplitude. Asthe point O is equidistant from S1 and S2 the displacement will be in the same phaseand it will produce maximum intensity. The intensity at any point P, distant y from O,depends on the path difference between the rays reaching P from S1 and S2. It will bemaximum, if the path difference (S2P – S1P) is even a multiple of half a wavelengthand minimum if it is odd multiple of half a wavelength.

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2dy 2dy dy

S2P + S1P 2D D

2

1

S P2 = D2 + (y + d/2)2

S P2 = D2 + (y - d/2)2

Figure 18

S P2 S P2 (y + d/2)2 (y - d/2)22 1

= 2dy

Path difference S2P - S1P =

For maximum intensity

Fringe width x = yn -yn-1

dy = n λ

D

y =D

n λd

Dn λ -

D(n-1) λ =

Dλ

d d d

λ = xd

D

By measuring x, d and D, the wavelength of monochromatic light can be determined.When a monochromatic light source is incident on the refracting edge of the biprism,splits into two halves of the Biprism. The light appears to diverge from two virtualslits, S1 and S2, separated by a small distance d. Since these sources are “coherent”,interference fringes will be produced, where the two beams of light overlap. Thefringe width, x, observed at a distance D cm from the slit is given by

xD λd

λ = ...............nm

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To get the interference pattern clearly, we use monochromatic laser source, fromwhich we get two images that is also of same wavelengths and interference patternobserved at certain distance.

A

S1 N

S B DM

S2C

Figure 19Setup of optical bench for Fresnel Biprism :

Figure 20

The optical bench is approximately 1 and half meter long, sufficient length for theseexperiments. The components used can be mounted on carriages that slide along thebench and have calibrated vernier scales to enable accurate determination of theirposition. The carriage height can be adjusted, but the horizontal position of the mountis fixed. The components have slots in their base to fit onto the carriages. In thisoptical bench at the left end monochromatic (laser) source, on the second standFresnel Biprism, on third stand of optical bench we place convex lens to converge theimage on the fourth stand concave lens for clear vision of fringes (interferencepattern) and on the fifth stand viewing screen place to observe bright and darkalternate fringes as shown in figure 20.

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Objective :

Experiment 1

Determination of wavelength of monochromatic light with the help of FresnelBiprism

Equipments Needed :

1. Optics bench

2. Sliding Stands (3)

3. Fix stands (2)

4. Uprights (3)

5. Monochromatic light source (laser light)

6. Fresnel biprism

7. Convex lens

8. Concave lens

9. Screen

10. Screen holder

11. Holding rod

Safety :

Never look directly into the laser beam or stare at its bright reflections-just as youshould avoid staring at the sun or other light sources.

Procedure :

1. Place the optics bench in the dark room and adjust the height of the bench withthe help of leveling screw.

2. Fix the laser light source with a holding rod.

3. Now mount the light source on the first fix stand at 0 cm mark of the opticsbench.

4. Fix the biprism on the upright and mount it on the first sliding stand just near tothe laser source.

5. Fix the screen in the screen holder and mount it on the second fix stand.

6. Switch ON the laser light.

Precaution : Laser light must fall on the refracting edge of Biprism.

Note : Adjust the heights of all uprights to be nearly the same i.e., all aligned insame plane.

8. Adjust the Biprism position with the help of sliding stand screw.

9. Move the screen along the optics bench till well defined (sharp and intense)refractive images are not formed on screen.

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Note : Two virtual images must be seen distinctly.

Figure 21

10. Observe the distance (d) between the images which is obtained due to refraction(as shown in figure 21).

Precaution: Distance between biprism and screen should be minimum.

11. Measure the distance (d) with the help of scale provided on screen which isabout 1 mm.

12. Tabulate the reading in given observation table 1.

Observation Table 1 :

S. No. Position of first image(b) in mm

Position of secondimage (c) in mm

d = c-b

1.

2.

Mean d =

For obtaining the fringe width :

13. Shift the screen at the end of optics bench. Laser and biprism positions are sameas previous.

Note : The positions of laser source and biprism must not be disturbed in wholeexperiment.

14. Fix the convex and concave lens on the two uprights.

15. Mount the convex and concave lens on the second and third sliding standrespectively.

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Note : Both lenses are used to focus the interference pattern.

16. Setup is arranged as shown in figure 22.

Figure 22

17. Adjust the position of both the lenses with the help of the sliding stand screw(horizontally and vertically) to obtain clear fringes (as shown in figure 23).

Figure 23

18. To observe the fringes more clearly turn the screen and also a concave lens witha very small angle.

19. Note the number of fringes in 1 cm which will give value of ‘x’.

Note : Scale is provided on screen to take the width in cm corresponding to thenumber of fringes and then convert into mm.

20. Distance between screen and source i.e., ‘D’ (in cm) change into mm tabulate ingiven observation table 2.

21. Now move screen by 2 cm towards source and again repeat the procedure 17 to20 and note down the reading in given observation table 2.

For more appropriate result or for clear vision observe the fringes at a fardistance from source like on the wall about 200 cm distance from the source.Determine the fringe width with the help of vernier caliper.

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Observation Table :

Figure 24

Position of uprightsS no.

Source(A)

Screen (B) D = B-A (inmm)

Number offringes (n) in

1 cm

Fringewidth x =10/n (in

mm)

1.

2.

3.

Mean value of D =…………..mm

Mean value of x =………..10

mm = mmn

22. All the values i.e., d, D and x should be in mm.

23. Put all the values in formula

λ xd

Dλ = ...............nm

Note : Some conversion are 1cm = 10mm

1m = 1000 mm

1m = 100 cm

1m = 109 nm

1cm = 107 nm

1 mm = 106 nm

24. To determine the Percentage Error

Percentage error =Actual value - Calculated value

Actual value100%

NV6028


Objective :

Experiment 2

Determination of fringe width by interference pattern

Equipments Needed :

1. Optics bench

2. Sliding Stands (3)

3. Fix stands (2)

4. Uprights (3)

5. Laser source

6. Fresnel biprism

7. Convex lens

8. Concave lens

9. Screen

10. Screen holder

11. Holding rod

Procedure :

1. Fix the laser light source with a holding rod.

2. Now mount the light source on the first fix stand at 0 cm of the optics bench.

3. Fix the biprism on the upright and mount it on the first sliding just near to thelaser source.

4. Fix the convex and concave lens on the two uprights.

5. Mount the convex and concave lens on the second and third sliding standrespectively.

Note : Both lenses are used to focus the interference pattern.

6. Fix the screen in the screen holder and mount it on the second fix stand.

Note : This stand must be at the maximum distance from laser source.

7. Setup is as arrangements shown in figure 25.

8. Switch ON the laser light.

Precaution : Laser light must fall on the refracting edge of Biprism.

NV6028


Figure 25

9. Adjust the position of both the lenses with the help of sliding stand screw(horizontally and vertically) to obtain clear fringes (as shown in figure 26).

Figure 26

10. To observe the fringes more clearly turn the screen and also the concave lenswith a very small angle.

11. For the particular number of fringes (10 or 15) take the reading on screen.

Note : Scale is provided on screen to take the width in cm corresponding to theno. of fringes.

12. For more appropriate result or clear fringes observe the fringes at a far distancefrom source like on the wall about 200 cm distances from the source. Determinethe fringe width with the help of vernier caliper.

Figure 27

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13. Note the readings of fringe width.

14. Tabulate the readings in the given observation table.

Observation Table :

Metal plate scale reading (in cm)S no. Number offringes (n)

1st fringe(a)

nth fringe(b)

Difference b-a

x = (b-a)/n (incm)

1.

2.

3.

Mean of fringe width x = ………..

15. With the help of this formula

xb-a

n

Fringe width x =……..cm

NV6028


Warranty

1) We guarantee the product against all manufacturing defects for 24 months fromthe date of sale by us or through our dealers.

2) The guarantee does not cover perishable item like cathode ray tubes, crystals,batteries, photocells etc.

3) The guarantee will become void, if

a) The product is not operated as per instruction given in the instructionmanual.

b) The agreed payment terms and other conditions of sale are not followed.

c) The customer resells the instrument to another party.

d) Any attempt is made to service and modify the instrument.

4) The non-working of the product is to be communicated to us immediately givingfull details of the complaints and defects noticed specifically mentioning thetype, serial number of the product and date of purchase etc.

5) The repair work will be carried out, provided the product is dispatched securelypacked and insured. The transportation charges shall be borne by the customer.

List of Accessories

1. Optics Bench (1.5 m)………………………………..……..….1 No.

2. Fresnel Biprism………………………………………….…….1 No.

3. Fix Stands………………………………………….………….2 Nos.

4. Sliding Stands…………………………………….…………..3 Nos.

5. Laser Light Source…………………………………………….1 No.

6. Holding Rod…………………………………………………...1 No.

7. Holding Uprights……………………………………….…..…3 Nos.

8. Screen…………………………………………………………1 No.

9. Screen Holder……………………………………….……...…1 No.

10. Concave Lens (f=20cm, d=75mm)……………………………1 No.

11. Convex Lens (f=10cm, d=50mm)…………………….………1 No.

12. e-Manual……………………………………………..………..1 No.

NV6028 New

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