Engineering Physics Unit-IV: Interference and Diffraction
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Questions and Answers

What is the fundamental requirement to get a well-defined interference pattern?

  • The phase difference between the two waves should be constant. (correct)
  • The two sources should have different wavelengths.
  • The two sources should have different amplitudes.
  • The two sources should have different frequencies.

    • What is the correct definition of temporal coherence?

  • Measure of phase relation between the waves reaching at two different points in space at different times.
  • Measure of phase relation between the waves reaching at two different points in space at the same time.
  • Measure of phase relation of a wave reaching at two different points in space at the same time.
  • Measure of phase relation of a wave reaching at a given point at two different times. (correct)

    • What is the correct definition of spatial coherence?

  • Measure of phase relation between the waves reaching at two different points in space at different times.
  • Measure of phase relation between the waves reaching at two different points in space at the same time. (correct)
  • Measure of phase relation of a wave reaching at two different points in space at the same time.
  • Measure of phase relation of a wave reaching at a given point at two different times.

    • Why is it not possible to show interference due to two independent sources of light?

    <p>Because the phase difference between the two sources changes with time.</p> Signup and view all the answers

    What is the purpose of using virtual sources formed from a single source in interference experiments?

    <p>To produce coherent sources</p> Signup and view all the answers

    What is an example of interference of light taking place between waves from two sources formed due to a single source?

    <p>Interference by division of wave front</p> Signup and view all the answers

    What is the condition for constructive interference in a wedge-shaped thin film?

    <p>2µcos (r + θ) = (2n + 1) λ/2</p> Signup and view all the answers

    Why is a broad source or extended source necessary in an interference pattern experiment?

    <p>To allow the whole interference pattern to be visible</p> Signup and view all the answers

    What is the path difference produced in a Newton's ring experiment?

    <p>∆ = 2 µt cos (r+θ) - λ/2</p> Signup and view all the answers

    What is the phenomenon of bending of light around the corners of an obstacle and their spreading into the geometrical shadow?

    <p>Diffraction</p> Signup and view all the answers

    What is the type of diffraction where the source of light or screen or both are at a finite distance from the diffracting element?

    <p>Fresnel's diffraction</p> Signup and view all the answers

    What is the name of the scientist who explained the phenomenon of diffraction by considering the interference of innumerable secondary wavelets?

    <p>Fresnel</p> Signup and view all the answers

    What is the range of thickness for a thin film in optical medium?

    <p>0.5 𝜇𝑚 to 10 𝜇𝑚</p> Signup and view all the answers

    What is the path difference between the rays AB and DE in the case of reflected light?

    <p>2 µ t Cos r - λ/2</p> Signup and view all the answers

    What is the condition for constructive interference in the case of reflected light?

    <p>2 µt cos r = n λ</p> Signup and view all the answers

    What is the condition for maximum intensity at point C in Fraunhofer diffraction at a single slit?

    <p>α = πa sinθ / λ = 0</p> Signup and view all the answers

    What is the condition for minimum intensity in Fraunhofer diffraction at a single slit?

    <p>sinα = 0</p> Signup and view all the answers

    What happens when the path difference between the rays is an odd multiple of λ/2 in the case of reflected light?

    <p>The film will appear dark</p> Signup and view all the answers

    What is the expression for the resultant amplitude at point P due to a single slit?

    <p>R = A sin(πα)/(πa sinθ/λ)</p> Signup and view all the answers

    What is the difference between the conditions of maxima and minima in reflected and transmitted light?

    <p>They are opposite for reflected and transmitted light</p> Signup and view all the answers

    What is the path difference between the two waves originating from S1 and S2 in Fraunhofer diffraction at a double slit?

    <p>b sinθ</p> Signup and view all the answers

    Why do we see different colors in the pattern when white light is incident on a thin film?

    <p>Because only a few wavelengths of light satisfy the condition of maxima</p> Signup and view all the answers

    How many interference maxima and minima are observed in the diffraction pattern of a double slit?

    <p>Equally spaced maxima and minima</p> Signup and view all the answers

    What is the expression for the intensity distribution due to Fraunhofer’s diffraction at a double slit?

    <p>I = A^2 cos^2(φ/2)</p> Signup and view all the answers

    What is the condition for the nth order principal maximum in the grating spectrum?

    <p>(a + b) sin θ = nλ</p> Signup and view all the answers

    What is the condition for the absent spectra in the diffraction pattern?

    <p>(a + b) / a = n / m</p> Signup and view all the answers

    If a = b, which orders of the spectra will be absent?

    <p>2nd, 4th, 6th, ...</p> Signup and view all the answers

    If b = 2a, which orders of the spectra will be absent?

    <p>3rd, 6th, 9th, ...</p> Signup and view all the answers

    What is the maximum possible value of the angle of diffraction θ?

    <p>90°</p> Signup and view all the answers

    What is the maximum number of orders of spectra that can be visible in a given grating?

    <p>(a + b) / λ</p> Signup and view all the answers

    If (a + b) is between λ and 2λ, what is the maximum number of orders of spectra that can be visible?

    <p>n max &lt; 2</p> Signup and view all the answers

    What is the path difference between the diffracted ray from the two extreme ends of one slit?

    <p>An integral multiple of λ</p> Signup and view all the answers

    Why are there (N - 1) minima between two successive principal maxima?

    <p>Due to the positions of principal maxima</p> Signup and view all the answers

    What is the equation for the direction of the nth order principal maximum in the grating spectrum?

    <p>(a + b) sin θ = nλ</p> Signup and view all the answers

    What is the purpose of drawing a series of very fine, equidistant and parallel lines on an optically plane glass plate in a plane transmission diffraction grating?

    <p>To block light from passing through the lines</p> Signup and view all the answers

    What is the effect of increasing the number of slits (N) on the intensity of principal maxima in a diffraction pattern?

    <p>The intensity of principal maxima increases</p> Signup and view all the answers

    According to Huygen's principle, what happens to all points within each slit when illuminated by a plane wave front of monochromatic light?

    <p>They become the source of secondary wavelets</p> Signup and view all the answers

    What is the expression for the resultant amplitude R due to all waves diffracted from each slit in the direction θ?

    <p>R = Asin(α)</p> Signup and view all the answers

    What is the path difference between the waves originating from two consecutive slits in a plane transmission diffraction grating?

    <p>(a+b) sin(θ)</p> Signup and view all the answers

    What is the expression for the corresponding phase difference between the waves from any two consecutive slits in a plane transmission diffraction grating?

    <p>2π/λ(a+b) sin(θ)</p> Signup and view all the answers

    ما هو أحد أمثلة الاستخدامات ل-มوجات فوق السمعية؟

    <p>كل ما سبق</p> Signup and view all the answers

    ما هو الدور الرئيسي لشكل قاعة المحاضرات؟

    <p>تحديد جودة الصوت</p> Signup and view all the answers

    ما هو الهدف من وضع قاعة المحاضرات بعيداً عن حركة المرور المزدحم؟

    <p>تقليل الضوضاء</p> Signup and view all the answers

    ما هو عامل رئيسي في تحديد جودةالصوت في قاعة المحاضرات؟

    <p>کل ما سبق</p> Signup and view all the answers

    ما هو تحديد معادلة سابين لزمن الرجوع؟

    <p>زمن الرجوع يتناسب عكسياً مع معامل امتصاص الصوت</p> Signup and view all the answers

    ما هو تأثير زيادة حجم القاعة على جودة الصوت؟

    <p>يرفع من جودة الصوت</p> Signup and view all the answers

    ما هو قانون ستوكس الذي يعبر عن قوة الاحتكاك الليزdynmic عندما يتحرك جسم صغير سلس داخل سائل لزج؟

    <p>F = 6πηrv</p> Signup and view all the answers

    ما هو تعريف اللزوجة؟

    <p>خصية مادة تمنع الحركة النسبية بين طبقات السائل</p> Signup and view all the answers

    ما هو قانون نيوتن للزوجة السائلية الذي ينطبق على السائلات اللزجة؟

    <p>F = ηA dv/dx</p> Signup and view all the answers

    ما هو معادلة بواسييل لتدفق السائل من خلال أنبوب صغير؟

    <p>v = P(r^2 - x^2) / 4ηl</p> Signup and view all the answers

    ما هو النوع من المائع الذي يقبل معادلة Bernoulli؟

    <p>مائع مثالي</p> Signup and view all the answers

    ما هو الشرط لتدفق السائل من خلال أنبوب صغير؟

    <p>التدفق المستقر والمتوازي مع محور الأنبوب</p> Signup and view all the answers

    ما هو Tên من رأس الصحون في معادلة Bernoulli؟

    <p>رأس ال壓</p> Signup and view all the answers

    ما هو التطبيق العملي لمعادل Bernoulli في مجال الطيران؟

    <p>رفع الطائرة</p> Signup and view all the answers

    ما هو مق استر النسيج في معادلة بواسييل؟

    <p>A = πxr^2</p> Signup and view all the answers

    ما هو 名称 من الأداة التي تستخدم لقياس معدل جریان السائل في الأنابيب؟

    <p>فنتوري متر</p> Signup and view all the answers

    ما هو سرعة الخروج من السائل من حاوية عند ارتفاع 'h' فوق مستوى 'O' من الحاوية؟

    <p>√(2gh)</p> Signup and view all the answers

    ما هو adını من قاعدة التحميل المهمة في نظرية Bernoulli؟

    <p>قاعدة المحافظة على الطاقة</p> Signup and view all the answers

    ما är der Grund für die Entstehung von Ultraschallwellen im Rod AB?

    <p>Änderung der magnetischen Flussdichte</p> Signup and view all the answers

    Was ist die Bedingung für Resonanz imMagnetostrictions-Verfahren?

    <p>Die Frequenz des Oszillatorschaltkreises ist gleich der Frequenz des vibrierenden Rods</p> Signup and view all the answers

    Was ist die physikalische Größe, die durch die Formel v = √(Y/ρ) beschrieben wird?

    <p>Die Geschwindigkeit des Schallwellen</p> Signup and view all the answers

    Was ist die Gleichung, die den Massenstrom eines Fluids durch einen Rohr beschreibt?

    <p>m = v × a × ρ</p> Signup and view all the answers

    Was ist die Bedeutung der Kontinuitätsgleichung?

    <p>Es ist eine mathematische Aussage des Erhaltungssatzes der Masse für ein inkompressibles Fluid</p> Signup and view all the answers

    Was ist der physikalische Effekt, der auftritt, wenn ein mechanischer Druck oder eine mechanische Zugkraft auf ein bestimmtes Kristallmaterial wie Quarz ausübt?

    <p>Piezo-elektrischer Effekt</p> Signup and view all the answers

    ما هو الشكل الذي تتبعبه جسيمات السائل في جريان سطحي?

    <p>مسار مستقر متشابه</p> Signup and view all the answers

    ما هو الحد الأقصى للسريع الذي يصبح الجريان السطحي неприطما?

    <p>السرعة الحرجة</p> Signup and view all the answers

    ما هو النوع من الجريان الذي يحدث عندما يتدفق السائل في طبقات متوازية بدون أي اضطراب بين الطبقات?

    <p>جريان سطحي</p> Signup and view all the answers

    ما هو قانون بوازوي لحجم السائل الذي يتدفق خلال أنبوبкапيلي؟

    <p>V = πPr⁴ / 8ηl</p> Signup and view all the answers

    ما هو النوع من الجريان الذي يحدث عندما يتدفق السائل في طبقات متوازية مع وجود اضطراب بين الطبقات?

    <p>جريان مهيض</p> Signup and view all the answers

    ما هو السبب الرئيسي لحدوث جريان مهيض؟

    <p>الاضطراب بين الطبقات</p> Signup and view all the answers

    ما هو الفرق بين جريان سطحي وجريان مهيض?

    <p>السرعة والاضطراب معا</p> Signup and view all the answers

    ما هو الشكل الذي يتبعه السائل عندما يتدفق خلال أنبوبкапيلي?

    <p>مسار مستقر متشابه</p> Signup and view all the answers

    ما هو القانون الذي يصف علاقة بين حجم السائل والسرعة والقوة الاحتكاكية?

    <p>قانون بوازوي</p> Signup and view all the answers

    ما هو التعريف الصحيح للرنين؟

    <p>عندما يحدث صوت متعدد من الانعكاسات قبل أن يصبح أقل وضوحا.</p> Signup and view all the answers

    ما هو الوقت الذي يحتاجه الصوت ليعود إلى الأذن بعد الانعكاس؟

    <p>0.1 ثانية أو أكثر</p> Signup and view all the answers

    ما هو Zweck من समय الرنين؟

    <p>مجال زماني متساوي للصوت</p> Signup and view all the answers

    ما هو الشكل الصحيح لزمن الرنين؟

    <p>t = V / A</p> Signup and view all the answers

    ما هو الظروري ليكون القاعة الصوتية جيدة؟

    <p>يجب أن تكون القاعة في منطقة هادئة</p> Signup and view all the answers

    ما هو الشكل الصحيح لجملة امتصاص المواد في القاعة؟

    <p>A = ∑𝑛 𝛼𝑠 = 𝛼1𝑠1 + 𝛼2𝑠2 + […] + 𝛼𝑛𝑠𝑛</p> Signup and view all the answers

    Study Notes

    Here are the study notes for the text:

    Interference

    • Coherent Sources: Two sources are said to be coherent if they emit light waves of the same frequency, nearly the same amplitude, and are always in phase with each other.
    • Types of Coherence:
      • Temporal Coherence (Longitudinal Coherence): Measure of phase relation of a wave reaching a given point at two different times.
      • Spatial Coherence (Transverse Coherence): Measure of phase relation between waves reaching two different points in space at the same time.

    Thin Film Interference

    • Thin Film: Optical medium of thickness in the range of 0.5 μm to 10 μm.
    • Interference in Thin Film:
      • Reflected Light: Interference occurs between reflected light and transmitted light.
      • Transmitted Light: Interference occurs between transmitted light and reflected light.
    • Path Difference: Given by Δ = 2µt cos r - λ/2.
    • Conditions for Constructive and Destructive Interference:
      • Constructive Interference: 2µt cos r = nλ (bright fringe).
      • Destructive Interference: 2µt cos r = (2n + 1) λ/2 (dark fringe).

    Interference Due to Non-uniform Thin Film (Wedge Shaped Thin Film)

    • Wedge Shaped Thin Film: Path difference given by Δ = 2µt cos (r + θ) - λ/2.

    Newton's Ring Experiment

    • Newton's Rings: Interference pattern formed by a thin film of variable thickness, such as between a plane glass plate and a convex lens.
    • Experimental Arrangement: Monochromatic light is incident normally on the glass plate, and the interference pattern is viewed through a microscope.
    • Theory: The air film formed is of wedge shape, and the path difference produced is Δ = 2µt cos (r + θ) - λ/2.

    Diffraction

    • Diffraction: Phenomenon of bending of light around the corners of an obstacle and spreading into the geometrical shadow.
    • Fresnel's Diffraction: Diffraction phenomenon caused by the interference of innumerable secondary wavelets produced by the unobstructed portions of the same wave front.
    • Fraunhofer's Diffraction: Diffraction phenomenon caused by the interference of light waves from different parts of the same wave front.

    Fraunhofer's Diffraction at a Single Slit

    • Diffraction Pattern: Consists of a central bright band with alternate dark and bright bands of decreasing intensity on both sides.
    • Analysis and Explanation: The diffracted ray along the direction of the incident ray is focused at a point, and those at an angle θ are focused at a different point.
    • Path Difference: Given by Δ = α = (πa sinθ) / λ.
    • Intensity Distribution: Given by I = I0 (sin^2(α) / (α^2)).

    Fraunhofer's Diffraction at a Double Slit

    • Diffraction Pattern: Consists of a number of equally spaced interference maxima and minima.
    • Theory: The resultant amplitude due to all wavelets from each slit is given by R = (A / (2i)) (e^(iα) - e^(-iα)).
    • Intensity Distribution: Given by I = I0 (cos^2(φ/2)).

    Plane Transmission Diffraction Grating (N-Slits Diffraction/Diffraction due to double slits)

    • Definition: An arrangement consisting of a large number of close, parallel, straight, transparent, and equidistant slits, each of equal width a, with neighboring slits being separated by an opaque region of width b.
    • Theory: The resultant amplitude due to all wavelets from each slit is given by R = (A / (2i)) (e^(iα) - e^(-iα)).
    • Intensity Distribution: Given by I = I0 (sin^2(Nα) / (N^2 sin^2(α))).

    Absent Spectra with a Diffraction Grating

    • Definition: A spectrum that is not visible due to the path difference between the diffracted rays from the two extreme ends of one slit being equal to an integral multiple of λ.### Conditions for Absent Spectra

    • Dividing equation (2) by equation (1) gives the condition for absent spectra in the diffraction pattern: (a+ b) /a =n/m

    • When a = b (width of transparent portion equals width of opaque portion), n = 2m and 2nd, 4th, 6th, etc. orders of the spectra are absent

    • When b = 2a, n = 3m and 3rd, 6th, 9th, etc. orders of the spectra are absent

    Number of Orders of Spectra with a Grating

    • The number of visible spectra in a grating can be calculated using the equation: (a + b) sin θ = n λ
    • (a + b) is the grating element, equal to 1/N, where N is the number of lines per inch in the grating
    • Maximum possible value of the angle of diffraction (θ) is 90°, so sin θ = 1
    • Maximum possible order of spectra (N max) is (a+b)/λ
    • If (a + b) is between λ and 2 λ, n max depends on the grating element and wavelength of light

    Acoustics of Building

    • Acoustics is the study of sound, its generation, transmission, and reception in the form of vibration waves in matter.

    Echoes and Reverberation

    • Echo: a reflection of sound that is heard distinctly after the original sound has stopped, with a time delay of at least 0.1 seconds between the original sound and its reflection.
    • Reverberation: the persistence of sound in a room due to multiple reflections from walls, floor, and ceiling, even after the source of sound has stopped.

    Reverberation Time

    • Reverberation time is the time it takes for sound energy density to decrease to one millionth of its initial value after the source of sound has stopped.
    • Sabine's Formula: t = (V / A) * (ln(10^6)), where t is the reverberation time, V is the volume of the hall, and A is the total absorption.

    Requirements of an Acoustically Good Hall

    • Site selection: choose a quiet location away from noisy areas.
    • Volume: the hall should be large enough to allow for uniform sound distribution.
    • Shape: the shape of the hall should be designed to minimize sound reflections.
    • Reverberation: the reverberation time should be optimal, not too long or too short.
    • Sound source: the sound source should generate sound of adequate intensity.

    Ultrasonic Waves

    • Ultrasonic waves: sound waves with frequencies higher than 20 kHz, beyond human hearing range.
    • Applications: sonar, echo sounding, cleaning, cutting, soldering, bloodless surgery, and tumor detection.

    Production of Ultrasonic Waves

    • Magnetostriction method: uses a rod of ferromagnetic material and an alternating magnetic field to generate ultrasonic waves.
    • Piezoelectric method: uses a crystal, such as quartz, that generates a potential difference when compressed or expanded, producing ultrasonic waves.

    Fluid Dynamics

    • Rate of flow: the volume of fluid that flows across a section of a pipe in unit time.
    • Continuity equation: the rate of fluid entering a region is equal to the rate of fluid leaving the region.

    Bernoulli's Theorem

    • Statement: the sum of pressure head, velocity head, and gravitational head remains constant for a fluid in steady flow.
    • Applications: atomizers, sprayers, airplane wings, velocity of efflux of liquid, venturimeter, and filter pumps.

    Stokes' Law of Viscosity

    • Statement: the viscous force opposing the motion of a small spherical body in a viscous fluid is proportional to the velocity of the body, the radius of the body, and the coefficient of viscosity.
    • Formula: F = 6πηrv.

    Viscosity and Coefficient of Viscosity

    • Viscosity: the property of a fluid that opposes the relative motion of its layers.
    • Coefficient of viscosity: the proportionality constant in Stokes' law of viscosity.

    Poiseuille's Equation

    • Derivation: assumes steady, parallel flow of a fluid through a capillary tube, with no radial flow or slip at the tube walls.
    • Formula: V = (Pπr^4) / (8ηl), where V is the volume of fluid flowing per unit time, P is the pressure difference, r is the radius, η is the coefficient of viscosity, and l is the length of the tube.

    Streamline Flow and Turbulent Flow

    • Streamline flow: a steady, parallel flow of a fluid, with each layer moving smoothly and steadily.
    • Turbulent flow: an unsteady, zigzag flow of a fluid, with many disturbances between layers.

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    Understanding interference and diffraction in Engineering Physics, including coherent sources and interference patterns.

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