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.

WAVES  Carry energy from one place to another  Classified by what they move through 1. Mechanical Waves medium 1. Mechanical Waves the energy is transferred by vibrations of medium (medium = matter) ex/ ocean waves move through water 2. Electromagnetic waves (EM Waves) 2. Electromagnetic waves (EM Waves) the energy moves through disturbances in the electromagnetic field. disturbances that transfer energy

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

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

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 90 0 (perpendicular) to wave pulse Surface Waves: Vibration is circular

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

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

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

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 10 8 m/s (commonly represented by the symbol c).

WAVE PROPERTIES 1.Amplitude 2.Wavelength 3.Frequency 4.Period 5.Velocity

AMPLITUDE crest trough 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 energy The energy of a wave is proportional to the square of its amplitude Determines loudness (sound) or brightness (EM wave)

WAVELENGTH WAVELENGTH   Distance between any two repeating points on a wave  cycle or oscillation  Also referred to as a cycle or oscillation   Determines what colors we see; what notes we hear (pitch)

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

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

VELOCITY v   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 v = ƒ

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

Reflection   Wave strikes a surface and is bounced back.  Law of Reflection  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

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

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  dispersion  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”

Refraction  Index of refraction  Index of refraction (n) – measure of how much a wave’s speed is reduced in a particular medium. Most frequently applied to light   n medium =   If the light does not change speed in the medium, the n value would be 1.0 n air = n glass = 1.52 n diamond = 2.42 n water = 1.33n cubic zirconia = 2.00 speed of light in vacuum = c vacuum speed of light in medium = c medium

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.

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

Diffraction Patterns

Interference   The combination of two or more waves that exist in the same place at the same time.  superposition  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  Constructive Interference (additive effect—in phase)  Destructive Interference  Destructive Interference (subtractive effect—out of phase)

Moiré Pattern

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

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