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Transcript

Electromagnetic Waves AP Physics Chapter 22 Vibration and Waves 22.1 Maxwell’s Equations 22.1 Maxwell’s Equations After the work of Oerseted, Ampere and Faraday James Clark Maxwell – all electric and magnetic phenomena can be described by four equations Fundamental – even taking into account relativity Require Calculus 22.1 22.1 Maxwell’s Equations 1. Gauss’s Law – relates electric field to electric charge 2. Magnetic field Law – 3. Faraday’s Law – electric field is produced by magnetic field 4. Ampere’s Law – magnetic field produced by an electric current, or changing electric field 22.1 Vibration and Waves 22.2 Production of Electromagnetic Waves 22.2 Production of Electromagnetic Waves How Electromagnetic Waves are Produced EMR Production The charged particle oscillate As it travels one direction a current is produced This generates a magnetic field When the direction changes, so does the current and the magnetic field 22.2 22.2 Production of Electromagnetic Waves Electric and magnetic fields are perpendicular to each other The fields alternate in direction These are electromagnetic waves Transverse In general – accelerating electric charges give rise to electromagnetic waves 22.2 Vibration and Waves 22.3 Electromagnetic Spectrum S-93 A hamster is out driving his fancy hamster wheel and yelling at a frequency of 1200 Hz. He approaches an observer at 65 m/s. If the observer runs away at 27 m/s, what is the apparent frequency that the observer hears? Assume that the air temperature is 27.5oC. 22.3 Electromagnetic Spectrum Electromagnetic Spectrum 22.3 22.3 Electromagnetic Spectrum All EMR has a velocity of in a Vacuum Velocity decreases with increase in optical density The wave equation becomes 300, 000, 000 m s 8 m s 3x10 c f Unlike Sound – energy depends on frequency E hf h 6.626 x10 34 J s 22.3 S-94 A mouse name Henry (French) plays a French Horn. If the air temperature is 22oC A. How long would the horn have to be to play 512 Hz as its fundamental frequency. Assume that it acts like a closed tube. B. What would be the velocity and wavelength of that frequency in the air? C. What are the next two harmonics that the French horn would produce? S-95 Next time you feel overweight, think of this cat. He has big bones. Good Luck on Your Test