pre class quiz 12-23

pre class quiz 12-23 - 3 Time-Averaged Power Which of the...

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Unformatted text preview: 3. Time-Averaged Power: Which of the following statements are true for timeiaveraged power? Student Response Value . Due to skin effect loss, the timeiaveraged power loss generally increases with increasing frequency. 25% . The timeiaveraged power is always a real quantity. 25% 3. For a dispersionless transmission line, the timeiaveraged power may vary with propagation distance. . For a lossless transmission line, the timeiaveraged power is a constant. 25% 1. Question wording One of these quantities osCIllates With a period equal to one half the wave period. Which one? Student Response Value 1. Time average power 2. Instantaneous power 100% 3. Both 4. Neither 3. Distortionless Transmission Line What of the following statements are true for a distortionless transmission line? Student Response Value @ 1. A lossless transmission line is always distrotionless 33.333% 2. A distortionless line will transmit signals well even ifit is coiled up a 3. A distortionless line tranmits signals of different frequenCies With the same phase velocity 33.333% 4. A distortionless line transmits signals of different frequencies with a phase velocity that is proportional to the frequency 5i 5. A transmissmn line is distortionless if RIG : LfC 33.333% 6. A distortionless line is lossless across all frequencies 3. VSWR and voltage maxima and minima which of the following statements are true: Student Response Value 1. When the load impedance is greater than the line impedance and both impedances are real, a voltage maXimum 25% occurs at the load. 2. The voltage maXima are separated by multiples of one wavelength. 3. when the load impedance is less than the line impedance and both impedances are real, a voltage minimum 25% occurs at the load. . VSWR is always larger or equal to 1 25% . For both short and open circuits, the voltage standing wave ratios are infinite. 25% 1. Input Impedance Which of the followmg statements about the input impedance ofa lossless transmissmn line are true? Student Response Value 51 1. For a half-wave length line, the input impedance is always equal to the load impedance. 25% 2. For a short-Circuit termination the input impedance is always real. 3. For a quarter-wave length line, the input impedance is always equal to the load impedance 4-. For an open-Circuit termination the input impedance is always imaginary 25% 5. The input impedance is the impedance experienced by the generator. 25% 5-1 6. when the terminating impedance is matched to the line, the input impedance is always equal to the 25% characteristic impedance of the line. 7. The input impedance is always equal to the characteristic impedance of the line. Score: 20,-“20 2. Quarter—wave matching Which of the following statements are true for quarter-wave matching? Student Response Value 1. Quarter-wave matching can be achieved over a very wide frequency range. 2. The line length can also be set at three quarters of the wavelength and still achieve the same effect. 33% 3. The impedance of the quarter wave line is determined by the impedances of the two transmission lines to be 33% Joined. 4-. Quarter-wave matching is often used to reduce reflections between two lines with different characteristics 34% impedances. Correct E1 BEE! Correct I Correct Correct CDI'I'ECI E3 Correcl 1. Short Circuit Stub which of the following statements about a short circuit stub on a transmission line are correct? Possible Answers 1. The short circuit stub ensures that there are no reflections that return to the load. 2. We need to control both the position and the length of the short circuit stub in order to match impedances. 3. Only the position of the short circuit stub is important in order to match impedances. 4. A short circuit stub matches the impedance between the transmission line and the load. 5. The addition of the short circuit stub results in power loss even when the short circuit stub is lossless. Score: mill] 2. Smith Chart which of the following quantities can be commonly derived from the Smith Chart? Possible Answers 1. Normalized load impedance . Reflection coefficient . Normalized input impedance 2 3 4. Standing wave ratio 5. Transmission line length 6 . Normalized impedance for any given position on the transmission line Score: 10f10 Which of the followmg statements are true about the Smith chart? Possible Answers 1. The constant r-circles on the Smith chart represent constant normallzed load impedance. 2. If the voltage standing wave ratio is known, then the magnitude of the reflection coefficient can be read dlrectly from the Smith chart. 3. If the reflection coefflCIent Is known, then the voltage standing wave ratio can be read directly from the Smlth chart. 4-. One CircumnaVIgatIon of the unlt cycle on the Smith chart Is eqUIvalent to a change of a full wavelength along the transmISSIon lIne. Score: 10310 2. Reflection diagram Which of the following statements are true for reflection diagram? Student Value Correct Answer Response 1. It can be used for harmonic wave analysis. 2. It is a 2-D plot, 34% :2 with the horizontal and vertical axes representing position and timer respectively. 3. It is a plot that 33% {5 shows the reflected voltage as well as reflected current. 4. It can help keep 33% {5 track of the voltage and current at any point on the transmission line. 1. Parallel Plate Waveguides which of these statements are true when the signal frequency increases? Student Response 1. The wave may become TEM-Iike if the frequency approaches to infinity. 2. The guide wavelength associated with a certain mode may decrease. 3. The wave impedance associated with each optical mode increases. 4. The number of modes that the signal may occupy increases. 5. The phase velocity increases. Dielectric Waveguides Which of the foilowing statements are true for a dieiectric waveguide? (note that more than one answer may be correct). Student Response Value Correct Answer . Some of the wave travels in the cladding as an evanescent wave. 33% Q . The maximum angie of wave propagation is determined by the core-cladding criticai angie. 33% Q . Eecause of the evanescent waves, signal power is iost even in a perfect (Iossiess) dielectric. 733% . For waveguiding to occur, the core must have a greater refractive index than the cladding. 34% 5 Score: 10.05l15 Dielectric waveguides vs conducting waveguides Match up the sentences: For conducting waveguides, the reflection coefficient at the boundary is compiex For dielectric waveguides, the reflection coefficient at the boundary is reai pureiy imaginary Statement Response Value Correct Match For conducting waveguides, the reflection coefficient at the boundary is reai 50.0% real For dieiectric waveguides, the reflection coefficient at the boundary is compiex 50.0% complex 1. Radiation Resistance The radiation reSistance of an antenna is defined as: Student Response Value Corre: 1. The eiectrical resistance of the antenna 2. The equivalent reSIstance that would dissipate the same amount of power as is lost from the antenna without being radiated, for the same current 5'. 3. The eqUivalent resistance that would dissipate the same amount of power as the antenna broadcasts for a 100% Q given current. 4. The ability of the antenna to withstand radiation 1. Transverse EM waves Which of the following statements are true for transverse EM waves: Student Response Value Correct Ai 1. Its propagation speed in vacuum depends on the frequency 2. Both E and H fields lie in the transverse plane normal to the direction of propagation 50% g 3. The electric field is always pointing to a fixed direction during wave propagation 4. Both E and H fields have constant magnitude but the phase can vary with time 5 Score: 7.5;‘15 2. Intrinsic impedance of free space Which of the following statements are true for intrinsic impedance of free space? Student Response Value Correct Ai 1. It can be positive or negative depending on the wave propagation direction. 2. It is N 377 ohm and is independent of the EM waves. 50% Q 3. It describes the ratio of electric field to magnetic fieid and therefore can be a complex number. 4. It has the same unit as that of the characteristic impedance of a transmisSIon line. 50% Q Score: 15,-“15 1. Lossy media A lossy medium may be modeled using: Value 50% Student Response . A complex permittiVity . A purely real impedance . A purely imaginary permittivity 50% 1 2 3 5i 4. A complex impedance 5. A purely imaginary impedance 6. A purely real permittivity Score: 10;“ 10 2. Attenuation coefficient The attenuation coefficient is given in units of Correct Answer M Student Response Value 1. Volts/metre l2. i 3. Ampfmetre Nepers 4. Nepersfmetre 100% Score: 1.0le 3. Dielectrics Which of the folloWIng statements are true? Corre Ct Answer Student Response Value In lossy dielectrics, E and H fields are generally out of phase. i 1. 2. The loss of a dielectric is generally frequency dependent 25% 3. EM waves in a dielectric generally have shorter wavelength compared to the same EM wave in free 25% space. 4. Damping loss is mainly responsible for E-field loss in dielectrics. 25% Score: 7.5/10 1. Origins of loss In a lossy dielectric, loss is modeled as if was caused by: Corre Ct Answer a M a M Value 100% Student Response A conduction current 39 album»- A displacement current Wave scattering None of the above Score: 15,115 2. Loss tangent Which of the folloWing statements about loss tangent are true? Correct Answer M Value 34% Student Response 1. The loss tangent is a measure of attenuation in a medium. I 2. The loss tangent ofa metal is small. I 3. The loss tangent measures loss in waves that are tangential to the medium. 33% 33% 4. The loss tangent generally decreases as the frequency increases. 5. The loss tangent of a vacuum is zero. Score: 15/15 1. Poynting vector units The 51 unit for the Poynting vector is (where “1‘” indicates to the power of): Correct Answer a Student Response Value W W/m"3 me W/mAZ me"2 100% WPWNH Score: 15,115 1. Poynting vector statements What of the folloWing statements about the Poynting vector are true? Correct Answe r Student Response Value 1. ) If an EM wave is crossing a surface, the instantaneous value of the Poynting vector on that surface can never be zero. . The Poynting vector is a measure of the electromagnetic power floWing through a unit surface. 33% . The Poynting vector is a measure of the electromagnetic energy inside a volume. . If an EM wave is crossing a surface, the timeiaveraged value of the Poynting vector on that 33% surface can never be zero. . The Poynting vector is in the same direction as the wave vector. 34% 15,115 Correct Answe r 1. Skin depth which of the following statements about the skin depth are true? Eh Hi SCOTS: 1. 2. 3. 4. Student Response The skin depth is the distance into the material at which the wave amplitude has decayed by lfe of its initial value. Skin depth tends to increase with frequency. All of the wave amplitude is confined within the skin depth. The skin depth for a material with high loss is smaller than the skin depth of a material with low loss (at the same frequency). 15,i'15 2. Signal transmission in a conductor which of the following statements are true for signal transmission in a conductor? Eh SCOTS: Err-hulk) Student Response . The skin depth of a conductor is directly proportional to the signal wavelength. The effective resistance of conductors tends to decrease with the increase of frequency. The H-fleld and E-fleld are generally out of phase. A conductor with a high loss tangent will also have a large skin depth. The effective resistance of conductors tends to increase with the increase of frequency. 15,115 1. Perfect conductors: An EM wave is incident onto a perfect conductor. which of the followmg statements are true? ii Score: 5. Student Response All of the wave is transmitted into the conductor. The electric field amplitude at the surface of the conductor must be zero. . The space between the maxima of the standing wave is equal to the wavelength of the incident wave. . At certain points the standing wave amplitude is always zero. A standing wave exists in the region of space in front of the conductor. 15y15 2. Dielectric interface Value 50% 5 U “fa Value 33% 3 3 “fa 3 4% Value 3 4% 3 3 “fa 3 3 “Va Correct Answer Q Correct Answer Q Q C orrect Answer Q An electromagnetic wave is incident from one lossless dielectric medium onto another medium which has a higher impedance. which of the following statements are true? SCOFE: m-P-LLJNH Student Response The reflection coefflCient is the ratio of the reflected wave power to the transmitted wave power. Because the media are lossless the standing wave ratio will be infinite. All the power is transmitted into the second medium. A fraction of the power is transmitted into the medium and the remaining power is reflected. The reflection coefflCient is the ratio of the reflected wave amplitude to the incident wave amplitude. 7.5115 1. Standing wave ratio For plane waves the standing wave ratio is defined as: SCOTS: Student Response . The ratio of the maXimum wave amplitude to the minimum wave amplitude. . The ratio of the maXimum time averaged wave power at any point to the minimum time averaged wave power at any point the peak wave amplitude at any point. . The ratio of the horizontal to vertical polarization amplitudes 15,i'15 2. Standing wave ratio calculation Value 750% 5 0 “fa 5 0 “fa Value . The ratio of the maximum value of the peak wave amplitude at any point to the minumum value of 100% The standing wave ratio is found to be 2.4-. This implies that the fraction of power reflected from the interface is SCOTS: #mMi—n Student Response 41% 64% 29% 17% 15,i'15 Value 100% C orrect Answer Correct Answer C orrect An 5W9 I' 1. Antireflection coating You need to make an antireflection coating on a substrate which has an impedance of 4 Ohms, where the incident medium has an impedance of 9 Ohms. which statement represents the correct conditions for the impedance and thickness of the coating layer? Student Response Value Correct Answer 1. Impedance=6 Ohms, Thickness=1,r‘2 wavelength in coating 2. Impedance=13 Ohms, Thickness=1f2 wavelength in vacuum 3. Impedance=6 Ohms, Thickness=1i8 wavelength In coating 4. Impedance=6 Ohms, Ti’Tlef‘IESS=1}'4 wavelength in coating 100% Q 5. Impedance:36 Ohms, Thickness:1f4 wavelength in vacuum Score: 15,115 2. Wave Impedance when reflections are present, the wave impedance for plane electromagnetic waves is defined as Student Response Value Correct Answer 1. The ratio of electric field strength to magnetic field intensity at any point 100% Q 2. The ratio of voltage to current at any point 3. The square root of permeability divided by permittivity 4-. The sum of the squares of the impedances of the incident and reflected medium Score: 15f15 1. Transverse wave phase front: The plane of phase constant (Le. the wavefront) of a transverse electromagnetic wave is: Student Response Value Correct Answer 1. always perpendicular to the magnetic field vector H 2. always perpendicular to the wavenumber vector k 100% Q 3. always perpendicular to the electric field vector E 4. always parallel to the wavenumber vector k Score: 15,:‘15 2. Wave vector question A transverse electromagnetic wave is travelling in the yiz plane. which of the folloWing statements about the wavenumber vector k is true Student Response Value Correct Answer 1. kz:0 2. ky:0 3. ky=0, kz=0 4. kx=0 100% Q Score: 15,115 1. Oblique incidence A plane wave is incident on a dielectric medium at an oblique angle. Which of the followmg statements are true? Student Response Value Correct Answer 1. All of the waves are reflected. ,fi 2. The angle of reflection is equal and opposite to the angle of incidence. 33% Q 3. The propagation angle of the wave transmitted into the material is equal to the angle of incidence. a 4. The sine of propagation angle of the wave transmitted into the material is equal to the sine of 33% Q angle of incidence multiplied by the refractive index of the first medium divided by the refractive index of the second medium. 5. The sine of the propagation angle of the wave transmitted into the material is equal to the sine of angle of incidence multiplied by the refractive index of the second medium dIVIded by the refractive index of the first medium. E. The reflection coefficient is a function of wave polarization. 34% Q 7. The reflection coefficient is independent of the wave polarization. Score: 301‘30 1. Special case Which of the following statements are correct? Angle beyond which total internal reflection occurs Student Response Value Correct Answer . The critical angle is the angle of incidence at which all p-polarized light is transmitted. . The angle of total internal reflection is a function of wave polarization. . Brewster's angle is the angle at which all s-polarized light is totally reflected. . Elrewster's angle is the angle at which p-polarization is totally transmitted. 33% Q . The critical angle is the angle of inCidence beyond which all of the inCident amplitude is reflected. 34% Q . A necessary (but not sufficient) condition for total reflection to occur, is that refractive index of 33% Q the incident medium be greater than the index of the transmitting medium. Score: 3U,r‘30 Summary: Special cases Will derive in class 2.5 6‘ l‘ 3 [W1 'r'm 5-“ A Los sless meclilml Low 10 53 me dium Good couduc for Units (3”J-"3'eiefil } (Sue’:1:>:2:>1) a: (Np-"1.11) B: l )2 (rad-"'m} E “I ‘5... 2 _ E \Pil-J—l (1 +1). up: I 1 1 r 6- if I (LIL-"5) 1.- p5 Jfl—g 1— g “#479”..- gm" 1.: I. (In) Dispersive media which of the followmg statements are true? A dispersive medium is a medium in which: Student Response Value Correct Answer 1. Different frequency components travel at different speeds. 50% Q 2. The real part of the dielectric constant is a function of frequency. 50% g 3. The real part of the dielectric constant is independent of frequency. 4. Different frequency components travel at the same speed. Score: 15,115 Group velocity Group velocity is: Student Response Value Correct Answer 1. Linearly proportional to the phase velocity. 2. The average speed of the Rolling Stones tour bus... 3. The speed of propagation of a modulation envelope. 100% Q 4. Just another name for phase velomty. Score: 15f15 ...
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pre class quiz 12-23 - 3 Time-Averaged Power Which of the...

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