Wave Propagation and Interface Behavior Quiz
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Questions and Answers

What happens to a plane wave when it obliquely incident on an interface between two materials?

  • It is completely absorbed by the material.
  • It will always reflect without any transmission.
  • It can be transmitted or reflected. (correct)
  • It cannot penetrate the interface at all.
  • How does the behavior of a wave at an interface depend on its polarization?

  • It remains unchanged regardless of polarization.
  • Only the angle of incidence impacts its behavior.
  • Different polarizations can lead to different ratios of reflection and transmission. (correct)
  • The type of wave determines whether it can transmit or reflect.
  • Which law governs the relationship between the angles of incidence and refraction in wave propagation?

  • Maxwell's Equations.
  • Newton's First Law.
  • Ohm's Law.
  • Snell’s Law. (correct)
  • What are the two types of oblique incidence based on the orientation of the electric field?

    <p>Parallel and Perpendicular. (B)</p> Signup and view all the answers

    At which specific angle does light behave differently at the interface due to total internal reflection?

    <p>Critical Angle. (C)</p> Signup and view all the answers

    What does the wave number or propagation vector represent in the wave equation?

    <p>Direction and magnitude of wave propagation (A)</p> Signup and view all the answers

    In the context of wave propagation, what does the symbol 'k' denote?

    <p>The wave number (B)</p> Signup and view all the answers

    Which of the following correctly defines the condition for lossless unbounded media?

    <p>k = β (D)</p> Signup and view all the answers

    What is true about parallel polarization (||) in wave interactions?

    <p>E is parallel to the plane of incidence (C)</p> Signup and view all the answers

    How can arbitrary polarization be analyzed?

    <p>By separating E into its normal and parallel components (B)</p> Signup and view all the answers

    What does the plane of incidence describe?

    <p>The direction of wave propagation and the normal to the surface (A)</p> Signup and view all the answers

    What role do ε, μ, and σ play in wave propagation between two media?

    <p>They are parameters that describe the electromagnetic properties of the media (B)</p> Signup and view all the answers

    What relationship does 'β' express in the context of wave behavior?

    <p>The wave vector in a given medium (D)</p> Signup and view all the answers

    What is the expression for the transmitted electric field intensity in terms of the incident electric field intensity using the transmission coefficient?

    <p>$E_{to} = \tau_{\perp} E_{io}$ (A), $E_t = \tau_{\perp} E_{io} e^{-j\beta_2 (x sin \theta_t + z cos \theta_t)}$ (B)</p> Signup and view all the answers

    What value do Γ⊥ and τ⊥ reduce to when the angles θi and θt are both zero?

    <p>$\Gamma = \tau = \frac{\eta_2 - \eta_1}{\eta_2 + \eta_1}$ and τ = 1 (A)</p> Signup and view all the answers

    How is the transmission coefficient τ⊥ calculated?

    <p>$\tau_{\perp} = \frac{\eta_2 cos \theta_i - \eta_1 cos \theta_t}{\eta_2 cos \theta_i + \eta_1 cos \theta_t}$ (C)</p> Signup and view all the answers

    What does the symbol β represent in the context of transmitted electric field equations?

    <p>The phase constant associated with the transmitted medium. (D)</p> Signup and view all the answers

    Which law relates the angles of incidence and transmission in this context?

    <p>Snell's law (B)</p> Signup and view all the answers

    If the incident electric field intensity is Eio = 100 V/m, what is the amplitude of the transmitted electric field intensity Eto when τ⊥ is assumed to be 0.5?

    <p>50 V/m (A)</p> Signup and view all the answers

    What characterizes the polarization of the electric field in the discussed scenario?

    <p>Perpendicular polarization (B)</p> Signup and view all the answers

    What is the effect of increasing the relative permittivity (εr) of the plastic on the transmission coefficient τ⊥?

    <p>It increases τ⊥ and decreases Γ⊥. (D)</p> Signup and view all the answers

    What is the value of $\theta_r$ based on the relation provided?

    <p>$\theta_i$ (B)</p> Signup and view all the answers

    Which of the following represents the relationship between $\eta_1$ and $\eta_2$?

    <p>$\eta_1 = 2\eta_2$ (C)</p> Signup and view all the answers

    What is the value of $\tau_{\perp}$ based on the equation derived?

    <p>$0.618$ (D)</p> Signup and view all the answers

    When deriving $\sin \theta_t$, what condition is used?

    <p>$\sin \theta_t = \sin \theta_i \cdot 0.25$ (B)</p> Signup and view all the answers

    What does $\epsilon_1$ equal according to the equations given?

    <p>$\epsilon_o$ (B)</p> Signup and view all the answers

    What is represented by the time-averaged Poynting vector $S_t$?

    <p>The average energy flow per unit area over time (A)</p> Signup and view all the answers

    Which trigonometric values are used in the calculation of the time-averaged power density?

    <p>sin(θ_t) = 0.25, cos(θ_t) = 0.968 (B)</p> Signup and view all the answers

    In the expression for the average power density $S_t$, what is the role of $\eta_2$?

    <p>It is a scaling factor related to the impedance (C)</p> Signup and view all the answers

    What does the vector $E_t$ depend on in the provided equations?

    <p>The sinusoidal function of position and time (A)</p> Signup and view all the answers

    If $\sin(\theta_t) = 0.25$, what is the approximate value of $\cos(\theta_t)$ based on the given information?

    <p>0.968 (A)</p> Signup and view all the answers

    What equation is used to express $S_t$ in terms of the vectors involved?

    <p>$S_t = Re(E_t \times H_t)$ (B)</p> Signup and view all the answers

    What does $\tau_{\perp} E_{io}$ signify in the equations?

    <p>The amplitude of the electric field (B)</p> Signup and view all the answers

    What is the final expression for the average power density $S_t$ given the values?

    <p>$S_t = 2.533a_x - 9.8a_z$ (D)</p> Signup and view all the answers

    What is the correct expression for the unit vector of the incident wave?

    <p>𝐚𝑥 sin 𝜃𝑡 + 𝐚𝑧 cos 𝜃𝑡 (A)</p> Signup and view all the answers

    What does the symbol $k_t$ represent?

    <p>The incident wave vector (A)</p> Signup and view all the answers

    Which direction is the reflected wave propagating in terms of its components?

    <p>In both the +ve $x$ and -ve $z$ directions (D)</p> Signup and view all the answers

    How is the phase constant for the reflected wave defined?

    <p>It is equal to $eta_1$ (A)</p> Signup and view all the answers

    What is the significance of obtaining the propagation vector $k$ for wave analysis?

    <p>It allows for the decoupling of wave components (C)</p> Signup and view all the answers

    The wave vector for the incident wave is expressed as a combination of which components?

    <p>The x and z-components (D)</p> Signup and view all the answers

    What mathematical representation is used for the unit vector of the reflected wave?

    <p>𝐚𝑥 sin 𝜃𝑟 - 𝐚𝑧 cos 𝜃𝑟 (C)</p> Signup and view all the answers

    In the context of wave propagation, what does $ heta_t$ represent?

    <p>The angle of transmission (C)</p> Signup and view all the answers

    Signup and view all the answers

    Flashcards

    Oblique Incidence

    When a plane wave hits a boundary between two materials at an angle, it behaves similarly to normal incidence. Part of the wave passes through (transmitted) and part of it bounces back (reflected). The way the wave acts at the boundary depends on its polarization.

    Snell's Law

    Snell's Law describes the relationship between the angle of incidence, angle of refraction, and the refractive indices of the two materials. It determines how much the wave bends as it passes from one material to another.

    Critical Angle

    The critical angle is the angle of incidence at which the refracted wave travels along the boundary between the two materials. Beyond this angle, there is only reflection and no transmission.

    Types of Polarization in Oblique Incidence

    In oblique incidence, there are two polarization types: parallel and perpendicular. Parallel polarization means the electric field is parallel to the plane of incidence, while in perpendicular polarization, the electric field is perpendicular to the plane of incidence.

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    Brewster Angle

    The Brewster angle is the specific angle of incidence where the reflected wave is completely polarized with its electric field perpendicular to the plane of incidence. This means no parallel polarized light is reflected.

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    Propagation Vector (k)

    The direction of propagation of a wave, represented by a vector.

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    Unit Propagation Vector (ak)

    The unit vector representing the direction of propagation of a wave, obtained by dividing the propagation vector by its magnitude.

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    Angle of Incidence (θt)

    The angle between the incident wave and the normal line to the boundary.

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    Angle of Reflection (θr)

    The angle between the reflected wave and the normal line to the boundary.

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    x-Component of Propagation Vector (kx)

    The component of the propagation vector in the x-direction.

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    z-Component of Propagation Vector (kz)

    The component of the propagation vector in the z-direction.

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    Wave Number ("beta")

    The magnitude of the propagation vector, representing the wave's speed in a specific medium.

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    Incident Wave Propagation Vector in z-direction (ktz)

    The component of the incident wave's propagation vector in the z-direction.

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    Propagation Vector (𝐤)

    Describes the direction of propagation of a wave. It is a vector quantity with components in the x, y, and z directions.

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    Plane of Incidence

    The plane formed by the direction of the incident wave (𝐤𝑖) and the normal vector to the surface at the point of incidence.

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    Parallel Polarization (||)

    The electric field vector is parallel to the plane of incidence. This means the electric field oscillates in the plane defined by the incident wave direction and the surface normal.

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    Perpendicular Polarization (⊥)

    The electric field vector is perpendicular to the plane of incidence. This means the electric field oscillates perpendicular to the plane defined by the incident wave direction and the surface normal.

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    Wave Number (k)

    The wave number or propagation constant, k, is a measure of how many waves occur in a given distance (usually in radians per meter).

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    Phase Constant (β)

    The phase constant, β, is a measure of the phase change of a wave per unit distance. For lossless media, it is equal to the wave number.

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    Poynting Vector (S)

    Describes the relationship between the electric field (E), magnetic field (H), and the direction of wave propagation (k). The Poynting vector is proportional to the cross product of E and H.

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    Wave Impedance (𝜂)

    The ratio of the electric field intensity to the magnetic field intensity in a medium.

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    Angle of Incidence (𝜃𝑖)

    The angle between the incident wave and the normal to the boundary between two materials.

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    Angle of Reflection (𝜃𝑟)

    The angle between the reflected wave and the normal to the boundary between two materials.

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    Angle of Transmission (𝜃𝑡)

    The angle between the transmitted wave and the normal to the boundary between two materials.

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    Time-averaged Poynting Vector (St)

    The time-averaged Poynting vector represents the average power density of an electromagnetic wave. It's a vector quantity and provides information about the direction and magnitude of power flow.

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    Calculating St

    The time-averaged Poynting vector for a plane wave traveling in a lossless medium is calculated as the real part of the cross product of the electric and magnetic field vectors.

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    Power Density

    The power density is the amount of power per unit area, and in this context, it represents the intensity of the electromagnetic wave.

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    Units of St

    The unit of power density is Watts per square meter (W/m²).

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    Wave Impedance (η)

    The wave impedance (η) is a property of the medium that the electromagnetic wave is traveling through and influences the relationship between the electric and magnetic fields. It's a complex quantity in general.

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    St Dependence on E and η

    The time-averaged Poynting vector is proportional to the square of the electric field magnitude and inversely proportional to the square of the wave impedance.

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    Parallel Polarization

    The polarization of an electromagnetic wave refers to the orientation of the electric field vector. When the electric field is parallel to the plane of incidence, it's called parallel polarization.

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    Transmission Coefficient (𝜏⊥)

    The transmission coefficient (𝜏⊥) represents the fraction of the incident electric field that is transmitted into the second medium for perpendicular polarization.

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    Reflection Coefficient (Γ⊥)

    The reflection coefficient (Γ⊥) represents the fraction of the incident electric field that is reflected back into the first medium for perpendicular polarization.

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    Energy Conservation Equation

    The equation 1 + Γ⊥ = 𝜏⊥ describes the conservation of energy at the boundary. The sum of the transmitted and reflected power equals the incident power.

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    Transmission Coefficient and Snell's Law

    The transmission coefficient (𝜏⊥) can be expressed in terms of the angles of incidence (𝜃𝑖) and the refractive indices of the two media (𝜂1 and 𝜂2) using Snell's law.

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    Time-averaged Power Density

    The time-averaged power density transmitted into the second medium is calculated by multiplying the square of the transmitted electric field amplitude by the impedance of the second medium and dividing by 2.

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    Material Properties and Light Interaction

    The relative permittivity (𝜀𝑟) and relative permeability (𝜇𝑟) of a material determine its refractive index and, therefore, its effect on the transmission and reflection of light.

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    Perpendicular Polarization

    The perpendicular polarization refers to the case where the electric field of the light wave is perpendicular to the plane of incidence, which is defined by the incident ray and the normal to the boundary.

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    Study Notes

    Lecture 4: Oblique Incidence I

    • The lecture covers oblique incidence of waves, specifically focusing on the behavior of waves at an interface between two different media.
    • Waves experience changes similar to those observed during normal incidence.
    • A portion of the wave is transmitted, and a portion is reflected.
    • In some cases, only transmission or reflection occurs.
    • The wave's behavior at the interface depends on its polarization.

    Oblique Incidence

    • Waves arrive at an angle.
    • Snell's Law and Critical Angle are relevant concepts.
    • Two types of polarization are considered: Parallel and Perpendicular.
    • Brewster angle is also discussed.

    Introduction

    • A plane wave incident obliquely on an interface between two materials undergoes changes similar to those during normal incidence.
    • Part of the wave is transmitted and part is reflected.
    • Wave behavior at the interface depends on wave polarization.

    Introduction (cont.)

    • Uniform plane wave in general form: E(r, t) = E₀ cos(ωt - kr) aₑ
    • General phasor form: E(r) = aₑE₀e⁻ʲᵏ⋅ᵣ
    • Position vector: r = xax + yay + zaz
    • Wave number (propagation vector): k = kxax + kyay + kzaz
    • k = ω√μє
    • For lossless unbounded media, k =β
    • β = βₓax + βᵧay + βz az

    Introduction (cont.)

    • Plane of incidence: the plane described by the direction of propagation of the incident wave (kᵢ), i.e., the Poynting vector.
    • Normal to the surface at the interface.
    • Parallel Polarization (||): E is parallel to the plane of incidence.
    • Perpendicular Polarization (⊥): E is perpendicular to the plane of incidence.
    • Arbitrary polarization can be treated as a combination of the two components (parallel and perpendicular).

    Introduction (cont.)

    • Medium 1: ε₁, μ₁, σ₁
    • Medium 2: ε₂, μ₂, σ₂
    • β₁ = ω√ε₁μ₁
    • β₂ = ω√ε₂μ₂
    • kᵢ = β₁ sin θᵢ ax + β₁ cos θᵢ az
    • kᵣ = β₁ sin θᵣ ax – β₁ cos θᵣ az
    • kₜ = β₂ sin θₜ ax + β₂ cos θₜ az

    Introduction (cont.)

    • Incident wave can be viewed as two components.
    • One propagating in the +ve x direction with phase constant kᵢₓ
    • One propagating in the +ve z direction with phase constant kᵢz
    • kᵢ = kᵢₓax + kᵢz az = β₁ sin θᵢ ax + β₁ cos θᵢ az
    • Unit vector for the incident wave: αᵢₖ = kᵢ/|kᵢ| = (sin θᵢ ax + cos θᵢ az)/√(sin² θᵢ + cos² θᵢ)

    Introduction (cont.)

    • Similarly, reflected wave can be viewed as two components.

    Introduction (cont.)

    • Similarly, transmitted wave can be viewed as two components.

    Introduction (cont.)

    • Once k is known, E is defined such that aₖ ⋅ E = 0.

    Introduction (cont.)

    • Oblique Incidence on a Conducting Interface:
    • Incidence from a dielectric medium
    • Perfect conductor surface
    • No transmitted wave
    • Total tangential E must be zero at the interface (z = 0).

    Perpendicular Polarization

    • E is perpendicular to the plane of incidence
    • Incident E is in the +ve y direction
    • Eᵢ(r) = aᵧEᵢ₀e⁻ʲᵏᵢ⋅ᵣ
    • kᵢ = β₁ sin θᵢ ax + β₁ cos θᵢ az
    • Incident wave phase: kᵢ ⋅ r = β₁x sin θᵢ + β₁z cos θᵢ

    Perpendicular Polarization (cont.)

    • Incident H has -ve x and +ve z components
    • H₁(x,z) = [aₖᵢ x Eᵢ (x,z)]/η₁ =...

    Perpendicular Polarization (cont.)

    • Reflection coefficient, Γ = -1
    • Reflection angle θᵣ = incident angle θᵢ
    • The total electric field E at the interface is zero.

    Perpendicular Polarization (cont.)

    • Expressions for E and H are provided.
    • Time-averaged Poynting vector, S

    Parallel Polarization

    • E lies in the incidence plane
    • Incident E has two components: one in the +ve x direction, and the second in the -ve z direction
    • Incident H is perpendicular to the incidence plane (y-direction).

    Parallel Polarization (cont.)

    • Reflected fields inside medium 1.
    • Tangential components of the electric field at the interface (z=0) must be zero.
    • Expressions for E and H are provided

    Parallel Polarization (cont.)

    • Total fields in material 1.

    Oblique Incidence on Dielectric Interfaces

    • Incident wave produces a reflected wave in the same material.
    • Also, wave propagating in material 2.
    • Reflection angle, θᵣ, depends on the incident angle, θᵢ (Snell's law of reflection: ).
    • A relation between refraction angle, θₜ, and incidence angle, θᵢ, is needed.
    • The electric field, E, is perpendicular to the plane of incidence (y-direction).
    • Medium 1 (permittivity ε₁, permeability μ₁): no conductivity (σ₁ = 0).
    • Medium 2 (permittivity ε₂, permeability μ₂): no conductivity (σ₂ = 0)
    • Specific equations for the fields (E and H) are given in both media
    • Relationship between incident and transmitted angles is given
    • The tangential components of E and H are equated on both sides of the interface(z=0)
    • Equations to determine the reflection and transmission coefficients (Г and τ) are derived.

    Example Calculations

    • Calculations for time-averaged power density.
    • Explicit values for various parameters are provided.

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    Description

    Test your knowledge on wave propagation when a plane wave encounters an interface between two materials. This quiz covers the effects of polarization, laws of reflection and refraction, and specific behaviors like total internal reflection. Dive into the fundamental principles governing wave interactions and their mathematical representations.

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