Wave Behavior

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# Wave Behavior - PowerPoint PPT Presentation

Wave Behavior. Another McGourty-Rideout Production. The Physics of Waves. All waves follow the laws of physics no matter what type Waves can be reflected, refracted, diffracted, absorbed, scattered and experience interference . Reflection.

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## PowerPoint Slideshow about 'Wave Behavior' - jacob

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Presentation Transcript

### Wave Behavior

Another McGourty-Rideout Production

The Physics of Waves
• All waves follow the laws of physics no matter what type
• Waves can be reflected, refracted, diffracted, absorbed, scattered and experience interference
Reflection
• Reflection happens when a wave bounces off an obstacle.

Specular reflection: smooth surface

• Angle of incidence = angle of reflection

Diffuse reflection: rough surface

• Reflection in all directions because angle of incidence varies over the surface due to its roughness
Law of Reflection

angle of incidence= angle of reflection

Reflection
• An echo - example of a reflection
• Radar uses this principle to determine the size, characteristics of, and distance to an object
Refraction
• Occurs as waves move from one medium into another or within a medium, like air, that varies  in density or temperature
• Waves bend toward the normal when they move from a less optically dense medium (faster) to a more optically dense medium (slower)
• Waves bend away from the normal when the opposite is true
Snell’s Law of Refraction
• Angles are measured with respect to the normal
Index of Refraction

n = c / v

• nair =1.0003
• nwater = 1.33
• nvacuum = 1.00
• Can you explain why “n” is a naked number? Can it ever be less than 1?
Index of Refraction Redux

n=√εμ

ε = electric permittivity

μ = magnetic permeability

These describe how the material interacts with electric and magnetic fields

Atmospheric Refraction
• Causes gradual curve of light from stars and sun
• Makes sun visible 2-3 minutes before sunrise and after sunset
Dispersion

The index of refraction of real materials actually depends on the frequency of the light being bent.

Dispersion is the explanation for rainbows:

Each color has its own frequency 

Each gets slowed down differently 

Each comes out at a different angle

Diffraction
• Waves that have longer wavelengths, or lower frequencies, diffract better than high frequency waves
• Diffraction patterns are determined by both the size of the opening and the wavelength
Absorption
• Absorption happens when the medium has the ability to absorb the energy of the wave
• When the wave is absorbed, its energy is transferred to the medium and the wave is gone
• Gradual absorption as the wave penetrates the medium is called “attenuation”
• Absorption of only specific frequencies will leave “gaps” in the continuing wave spectrum called “spectral absorption lines”
Absorption
• Absorption at the quantum level happens when an individual photon has the exact energy that corresponds to an energy gap between two energy states of the medium
• The type of energy gap corresponds directly to the frequency of the photon
Scattering
• If the photon is absorbed and then re-emitted immediately, it is said to be scattered
• How the light is scattered is dependent on the frequency of the light and the size of the particle it is scattering from
• Some of the energy of the light is absorbed by the scatterer and so the re-emitted light has a little less energy
Scattering
• If the photon has a longer wavelength than the size of the scattering particle, it is called Rayleigh scattering
• In Rayleigh scattering the very long wavelength light is hardly scattered at all but the shorter wavelength is much more strongly scattered
• Since blue light is much ‘shorter’ than red, it gets more scattered by the molecules in the air: therefore the sky is blue!
Interference
• When two or more waves come together, they “superimpose” or add together
• The total amplitude is simply the sum (positive & negative!) of all the individual amplitudes
• The extremes of what can happen are called constructive interference and destructive interference

S

S

S

S

Destructive

(180° out of phase)

Partially Constructive

(somewhat out of phase)

Constructive

(in phase)

Non-coherent signals

(noise)

Interference Fringes
• Interference fringes are a series of bright and dark bands
• Sometimes straight, sometimes circular, sometimes more complicated
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