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Transcript
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 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 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 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 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 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 Resonance Natural frequency frequency of vibration determined by the object’s composition and shape Resonance when frequency of external force matches natural frequency 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 Electromagnetism Magnetic Fields generated by electric current Energy conversion electric motors electric generators speakers Maxwell’s Equations summary of electromagnetic laws and interactions… 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 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 Maxwell’s Equations Ampere-Maxwell Law relates magnetic field to electricity Maxwell unifies electricity and magnetism into electromagnetism Electromagnetic Interactions Transmission vs. opacity Absorption vs. emission Scattering refraction reflection diffraction interference 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 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] 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 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 blueshifted (towards)
