PY208N-Lecture-27

PY208N-Lecture-27 - Physics 208N-004 Lecture #27 25 March...

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1 Physics 208N-004 Lecture #27 – 25 March 2011 Chapter 31: 4-10 Electromagnetic waves , 32: 4 Refraction, 35:11 Polarization Since the current lags the voltage one of the circuit elements must be an inductor. Since the angle is less than 90º, the other element must be a resistor. We use 30-29a to write the resistance in terms of the impedance. Then using Eq. 30-27 to determine the impedance from the voltage and current and Eq. 30-28b, we solve for the unknown inductance and resistance.  22 2 2 2 rms rms rms rms 2 tan 2 cot 2 2 cot 2 2 1 cot 120V =5 1 . 5 m H 5 2 m H 2 1 cot 2 60Hz 5.6A 1 cot 65 2 cot 2 51.5mH cot65 9.1 fL Rf L R V Z R fL fL fL fL I V L fI L        82. A circuit contains two elements, but it is not known if they are L , R , or C . The current in this circuit when connected to a 120-V 60-Hz source is 5.6 A and lags the voltage by 65°. What are the two elements and what are their values? 31-4 Production of Electromagnetic Waves Close to the antenna, the fields are complicated, and are called the near field: An oscillation accelerates charge. Acceleration of charge generates electromagnetic waves!
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2 31-4 Production of Electromagnetic Waves Far from the source, the waves are plane waves: The electric and magnetic waves are perpendicular to each other, and to the direction of propagation. 31-5 Electromagnetic Waves, and Their Speed, Derived from Maxwell’s Equations In the absence of currents and charges, Maxwell’s equations become:
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3 31-5 Electromagnetic Waves, and Their Speed, Derived from Maxwell’s Equations This figure shows an electromagnetic wave of wavelength λ and frequency f . The electric and magnetic fields are given by where .
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PY208N-Lecture-27 - Physics 208N-004 Lecture #27 25 March...

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