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WAVES

WAVES. SP4. Students will analyze the properties and applications of waves. a. Explain the processes that result in the production and energy transfer of electromagnetic waves. b. Experimentally determine the behavior of waves in various media in terms of

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WAVES

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  1. WAVES SP4. Students will analyze the properties and applications of waves. a. Explain the processes that result in the production and energy transfer of electromagnetic waves. b. Experimentally determine the behavior of waves in various media in terms of reflection, refraction, and diffraction of waves. c. Explain the relationship between the phenomena of interference and the principle of superposition. d. Demonstrate the transfer of energy through different mediums by mechanical waves.

  2. WAVES disturbances that transfer energy • Carry energy from one place to another • Classified by what they move through • Mechanical Wavesthe energy is transferred by vibrations of medium (medium = matter)ex/ ocean waves move through water • Electromagnetic waves (EM Waves)the energy moves through disturbances in the electromagnetic field.

  3. Making a pulse MECHANICAL WAVES require a medium (the material through which the disturbance is moving) to transmit energy travel through & gradually lose energy to that medium • Examples: water, sound, rope, & spring waves

  4. MECHANICAL WAVES Pulse = direction of energy transfer Vibration = direction of vibration of medium relative to pulse

  5. MECHANICAL WAVES Classified by how medium vibrates Longitudinal Waves: Vibration is in the same direction as (parallel to) wave pulse Transverse Waves: Vibration is at 900 (perpendicular)to wave pulse Surface Waves: Vibration is circular

  6. Rarefaction (expansion) Compression LONGITUDINAL WAVES Vibration is parallel to the direction of the motion of the wave • Back and forth (compression & rarefaction) • Also called compression or pressure wave • Examples: P-type seismic waves, sound waves

  7. TRANSVERSE WAVES Vibration is perpendicular to the direction of the motion of the wave • Can be polarized vertically or horizontally • Examples: Electromagnetic (EM) waves, S-type seismic waves

  8. ELECTROMAGNETIC WAVES do NOT require a medium to transmit energy move with no loss of energy, so they can effectively travel forever • Examples: The electromagnetic spectrum

  9. ELECTROMAGNETIC WAVES do NOT require a medium to transmit energy • Electromagnetic waves are created by the vibration of an electric charge. • This vibration creates a wave which has both an electric and a magnetic component. • An EM wave transports its energy through a vacuum at a speed of 3.00 x 108 m/s (commonly represented by the symbol c). 

  10. WAVE PROPERTIES • Amplitude • Wavelength • Frequency • Period • Velocity

  11. AMPLITUDE • How far the medium moves from rest position (where it is when not moving) **the highest point is the crest, and the lowest point is the trough. • Gives indication of “power” or “strength” of wave • Does not affect velocity of wave • The energyof a wave is proportional to the square of its amplitude • Determines loudness (sound) or brightness (EM wave)

  12. WAVELENGTH • Distance between any two repeating points on a wave • Also referred to as a cycle or oscillation • Determines what colorswe see; what notes we hear (pitch)

  13. FREQUENCY ƒ • Equal to the number of wavelengths that pass any point per second • Measured in Hertz (Hz), or number of wavelengths in 1 second • Frequency is inversely proportional to wavelength f = 1/  • Frequency is directly proportional to energy

  14. PERIOD T • Amount of time for one wavelength to pass a point • Related inversely to frequency T = 1/ƒ

  15. VELOCITYv • the rate at which the energy travels; has speed & direction • Depends on medium • Mechanical waves travel faster through dense media • EM Waves are faster through less dense media • Velocity = wavelength x frequency v = ƒ

  16. FOUR WAYS WAVES INTERACT • R-R-D-I • REFLECTION • REFRACTION • DIFFRACTION • INTERFERENCE How waves interact with a medium How waves interact with other waves

  17. Reflection • Wave strikes a surface and is bounced back. • Law of Reflection: angle of incidence = angle of reflection Assumes smooth surface. Measured from normal. We only see objects because light is reflected to our eyes

  18. Specular vs. Diffuse Reflection • Specular Reflection • Mirror-like • Retains image • Diffuse Reflection • Energy reflects but not image.

  19. Refraction • Change in wave’s direction as it passes from one medium to another due to differences in speed of wave. • The greater the change in speed, the more the wave bends • Atmospheric refraction allows us to see mirages and the sun before it rises and after it sets • Rainbows are produced by dispersion – the refraction of each separate frequency of visible light • Fiber optics are made possible by refraction of light within glass “wire”

  20. speed of light in vacuum = cvacuum speed of light in medium = cmedium Refraction • Index of refraction(n) – measure of how much a wave’s speed is reduced in a particular medium. • Most frequently applied to light • nmedium= • If the light does not change speed in the medium, the n value would be 1.0 nair=1.0003 nglass = 1.52 ndiamond = 2.42 nwater= 1.33 ncubic zirconia = 2.00

  21. Snell’s Law • As a wave passes from low n to high n, it bends toward the normal. • As a wave passes from high n to low n, it bends away from the normal. • If n is the same for both media, the wave does not bend.

  22. Diffraction • The bending of waves around an obstacle. • Can let you hear sounds that originate behind an obstacle • Explains how waves can shape coastlines. • Explains the diffraction pattern produced in the double-slit experiment. • The amount of bending depends on the size of the obstacle and the size of the waves • Large obstacle, small wavelength = less diffraction • Small obstacle, large wavelength = more diffraction

  23. Diffraction Patterns

  24. Interference • The combination of two or more waves that exist in the same place at the same time. • When two or more waves come together, they “superimpose” or add together (superposition) • The total amplitude is simply the sum (positive & negative!) of all the individual amplitudes • Constructive Interference (additive effect—in phase) • Destructive Interference (subtractive effect—out of phase)

  25. Moiré Pattern

  26. S S S S Destructive (180° out of phase) Constructive and Destructive Interference Partially Constructive (somewhat out of phase) Constructive (in phase) Non-coherent signals (noise)

  27. Young’s Double Slit Experiment • Light diffracting through 2 slits produces fringes on a screen • Bright fringes are areas of constructive interference • Dark fringes are areas of destructive interference

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