* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 22.2 Production of Electromagnetic Waves Oscillating charges will
Electricity wikipedia , lookup
Waveguide (electromagnetism) wikipedia , lookup
Photoelectric effect wikipedia , lookup
Magnetic monopole wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Faraday paradox wikipedia , lookup
Magnetoreception wikipedia , lookup
Magnetochemistry wikipedia , lookup
Superconductivity wikipedia , lookup
Eddy current wikipedia , lookup
Multiferroics wikipedia , lookup
Wireless power transfer wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Maxwell's equations wikipedia , lookup
Electromagnetic compatibility wikipedia , lookup
Lorentz force wikipedia , lookup
Mathematics of radio engineering wikipedia , lookup
Computational electromagnetics wikipedia , lookup
Electromagnetic field wikipedia , lookup
Chapter 22 Electromagnetic Waves © 2006, B.J. Lieb Some figures electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey Giancoli, PHYSICS,6/E © 2004. Ch 22 1 Maxwell’s Equations 1. Coulomb’s Law ( Charges produce electric fields ) 2. Equation for Magnetic Field (Currents produce magnetic fields ) 3. Induction – changing magnetic field produces an electric field 4. Changing electric field produces a magnetic field # 4 was added by Maxwell Ch 22 Maxwell combined these equations and the result was an equation similar to a wave equation and thus he predicted a new type of wave consisting of electric and magnetic fields. Furthermore the equation predicted the velocity of this “new” type of wave and it was the velocity of light. This suggested that light was an electromagnetic phenomena. 2 22.2 Production of Electromagnetic Waves Oscillating charges will produce electromagnetic waves: Ch 22 3 Reception of Radio Waves •Oscillating vertical electric fields cause oscillating currents in the antenna. •Oscillating horizontal magnetic field can induce a oscillating current in a loop antenna Ch 22 Antenna 4 22.2 Production of Electromagnetic Waves The electric and magnetic waves are perpendicular to each other, and to the direction of propagation. Ch 22 5 Nature of Electromagnetic Radiation The success of Maxwell’s Equation appeared to be clear proof that light was a wave phenomena, but we will see in Ch 27 that Einstein suggested that light had a dual naturesome experiments show wave properties and others show particle properties. •For wave properties we use c = f where c is the speed of light, is the wavelength and f is the frequency. •For the particle properties light is a stream of particles called photons which have energy but have zero “rest” mass. The energy of a photon is proportional to its frequency. Ch 22 6 Electromagnetic Spectrum c f Ch 22 7 Electromagnetic Spectrum c f You are expected to know the order of the following parts of the electromagnetic spectrum. These are listed in order of increasing frequency and therefore in order of increasing energy of the photon. •Radio Waves •Microwaves •Infrared •Visible •Ultraviolet •X-Rays •Gamma Rays Ch 22 8 Ex 22-1: The antenna of a cell phone is often ¼ wavelength long. A particular cell phone has a 8.5 cm long straight rod for its antenna. Estimate the operating frequency of the phone. 1 L 8.5 10 m 4 2 4L (4) (8.5 10 m) 2 0.34 m v f v 3.0 10 m / s f 0.34 m 3 f 8.8 108 Hz 880 MHz Ch 22 9 22.7 Radio and Television; Wireless Communication The mixing of signal and carrier can be done two ways. First, by using the signal to modify the amplitude of the carrier (AM): Ch 22 10 22.7 Radio and Television; Wireless Communication Second, by using the signal to modify the frequency of the carrier (FM): Ch 22 11