Bài giảng Electromagnetic Fields - Chapter 6 - Trần Quang Việt

Nội dung text: Bài giảng Electromagnetic Fields - Chapter 6 - Trần Quang Việt

1. Electromagnetic Fields – Prob – ch_6 P6.5. In the system shown in Fig.6.64, assume that Vg is a constant voltage source of 100V and the switch S is closed at t=0. Find and sketch: (a) the line voltage versus z for t=0.2s; (b) the line current versus z for t=0.4s; (c) the line voltage versus t for z=30m; and (d) the line current versus t for z=-40m. S t=0        v =2x108m/s  8 p vp=3x10 m/s Vg z=-300m z z=0- z=0+ z z=300m Fig.6.64 © Trần Quang Việt – BMCS – Khoa Điện – ĐHBK Tp.HCM
2. Electromagnetic Fields – Prob – ch_6 P6.7. The system shown in Fig.6.66 is in steady state. Find (a) the line voltage and current, (b) the (+) wave voltage and current, and (c) the (-) wave voltage and current.      T s 100V z=0 z=l Fig.6.66 © Trần Quang Việt – BMCS – Khoa Điện – ĐHBK Tp.HCM
3. Electromagnetic Fields – Prob – ch_6 D7.4. A line of characterictis impedance 60 is terminated by a load consisting of the series combination of R=30, L=1H, and C=100pF. Find the values of SWR and dmin for each of the following radian frequencies of the source: (a) =108; (b) =2x108; and (c) =0.8x108. Ans: (a) 2,0; (b) 14.94, 0.309; (c) 3.324, 0.115 D7.5. Standing-wave measurements are performed on a line of characteristic impedance 60 terminated by a load ZR. For each of the following sets of the standing-wave data, find ZR: (a) SWR=1.5, a voltage minimum right at the load; (b) SWR=3.0, two successive voltage minima at 3cm and 9cm from the load; and (c) SWR=2.0, two successive voltage minima at 3cm and 7cm from the load Ans: (a) (40+j0); (b) (180+j0); (c) (48+j36) © Trần Quang Việt – BMCS – Khoa Điện – ĐHBK Tp.HCM
4. Electromagnetic Fields – Prob – ch_6 P7.2. In the system shown in the Fig.7.42. the line is open-circuited at the far end, the source voltage is: Vg(t) = V0cos( f0t)cos(3 f0t) and l=/4 at f=f0. Find the root-mean-square (rms) values of the line voltage and line current at values of d/l equal to 0, 1/3, ½ and 1. (Note: The rms value of the sum of the voltages of two harmonically ralated frequencies is equal to the square root of the sum of the square of the rms value of the individual voltages)  Open    Circuit Fig.7.42 Vg(t) d=l d d=0 © Trần Quang Việt – BMCS – Khoa Điện – ĐHBK Tp.HCM
5. Electromagnetic Fields – Prob – ch_6 P7.12. A slotted coaxial line of characteristic impendance 75 was use to measure an unknown load impendance. First, the receiving end of the line was short-circuited. The voltage minima were found to be 20cm apart. One of the minima was marked as the reference point. Next, the unknown impedance was connected to the receiving end of the line. The SWR was found to be 3.0 and a voltage minimum was found to be 6cm from the reference point toward the load. Find the unknown load impedance. © Trần Quang Việt – BMCS – Khoa Điện – ĐHBK Tp.HCM
6. Electromagnetic Fields – Prob – ch_6 P7.18. In the system in Fig.7.52, find : (a) the value of the load impedance Zg that enables maximum power transfer from the generator to the load; and (b) the power transferred to the load for the value found in (a). (Hint: apply maximum power transfer theorem at d=l)  (25+j50)    Zg   V d=l d=0 Fig.7.52 © Trần Quang Việt – BMCS – Khoa Điện – ĐHBK Tp.HCM