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HNRT 227 Fall 2015 Chapter 6

HNRT 227 Fall 2015 Chapter 6. Wave Motion, Sound and Electromagnetism 17 September 2015 presented by Prof. Geller. Recall from Chapters 1-5. Units of length, mass and time, and metric Prefixes Density and its units The Scientific Method Speed, velocity, acceleration Forces

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HNRT 227 Fall 2015 Chapter 6

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  1. HNRT 227 Fall 2015Chapter 6 Wave Motion, Sound and Electromagnetism 17 September 2015 presented by Prof. Geller

  2. Recall from Chapters 1-5 • Units of length, mass and time, and metric Prefixes • Density and its units • The Scientific Method • Speed, velocity, acceleration • Forces • Falling objects, Newton’s Laws of Motion and Gravity • Work, Potential Energy and Kinetic Energy • Conservation of Energy, Types/Sources of Energy • Kinetic Molecular Theory, Temperature and Heat • Phases of matter and Thermodynamics • Electricity • Magnetism

  3. Forces and Vibrations • Vibration • back and forth motion • Amplitude • extent of displacement from the equilibrium position • Cycle • one complete vibration • Period • time required to complete one cycle • Frequency • number of cycles per second • Relationship between period and frequency • T = 1 / f f = 1 / T

  4. Waves • Longitudinal • disturbance that causes particles to move closer together or farther apart IN THE SAME DIRECTION the wave is moving • Transverse • disturbance that causes motion PERPENDICULAR to the direction that the wave is moving • In general, liquids carry longitudinal waves but not transverse waves • Transverse waves, such as water waves, dissipate all their energy at the phase interface • We use same terms as vibrations, for waves • v = l * f

  5. Sound Waves • Sound does not travel in a vacuum • Sound moves through solids faster than any gas • Velocity of sound is effected by composition and temperature of gas

  6. Reflection, Refraction and Interference • Reflection • waves bouncing back off of a boundary • Refraction • change in direction of wave crossing a boundary • Interference • interaction of waves • destructive interference • constructive interference

  7. Resonance • Natural frequency • frequency of vibration determined by the object’s composition and shape • Resonance • when frequency of external force matches natural frequency

  8. Doppler Effect and Sonic Boom • Doppler Effect • Apparent change in frequency of a wave caused by the relative motion of the source or observer • pitch of train approaching, departing • Sonic boom • shock wave caused by object moving at speed of sound or faster

  9. Electromagnetism • Magnetic Fields • generated by electric current • Energy conversion • electric motors • electric generators • speakers • Maxwell’s Equations • summary of electromagnetic laws and interactions…

  10. Waves • Types of waves • longitudinal • e.g. sound • transverse • e.g. electromagnetic waves • Velocity, frequency and wavelength • wave velocity = wavelength times frequency • watch your units

  11. Electromagnetism • Electricity according to Gauss • relates electricity to electric charge • Faraday’s Law • relates electric fields to magnetic fields • Magnetism according to Gauss • relates magnetism to electricity

  12. Maxwell’s Equations • Ampere-Maxwell Law • relates magnetic field to electricity • Maxwell • unifies electricity and magnetism into electromagnetism

  13. Electromagnetic Interactions • Transmission vs. opacity • Absorption vs. emission • Scattering • refraction • reflection • diffraction • interference

  14. Electromagnetic Spectrum • Visible • Red (~7000 A or 700 nm) • Orange, Yellow, Green, Blue, Indigo • Violet (~4000 A or 400 nm) • More than meets the eye • radio, microwave, infrared, ROYGBIV (visible), ultraviolet, X-rays, gamma rays • from lowest energy to highest energy • from longest to shortest wavelength • from lowest to highest frequency

  15. Reflection and Refraction (not all in text) • Reflection • the angle of incidence is equal to the angle of reflection • qi = qr • Virtual image • light rays appear to originate from • Real image • light rays really do meet here • Refraction • change of direction of light • n = c / v [defines index of refraction]

  16. Diffraction, Interference and Polarization (not all in text) • Diffraction • light rays appear to bend around the edge of an object • Interference • light rays interacting with other light rays causing reinforcement or canceling or some combination of the two • Polarization • vibrates/oscillates in a single plane

  17. Doppler Shift • A change in measured frequency caused by the motion of the observer or the source • classical example of pitch of train coming towards you and moving away • wrt light it is either red-shifted (away) or blue-shifted (towards)

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