# physics notes waves and optics chapters 16-17, 24-26

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• Physics NotesWaves and Optics

Chapters 16-17, 24-26

• Wave - the motion of a disturbance that transmits energyComparing Types of Waves

1. Mechanical vs ElectromagneticMechanical - requires a medium to transfer energyie. slinky, water, sound, earthquakeElectromagnetic - requires no medium ie. radio, micro, IR, visual, UV, X, gamma

• 3. Transverse vs LongitudinalTransverse Particles or disturbance vibrate perpendicularly to the direction of energy transferie. light, slinkyLongitudinal - Particles vibrate parallel to the direction of the energy transfer (Pressure Wave)compression vs rarefractionie. sound, slinky

http://www.phy.ntnu.edu.tw/~hwang/waveType/waveType.html

http://www.explorescience.com/activities/Activity_page.cfm?ActivityID=50

• Transverse Waves

• Transverse and Longitudinal Waves

• Aspects of all SHM (including waves)

Amplitude (A) - maximum displacement from equilibrium (m) Intensity or Energy

Period (T) - time to complete 1 cycle of motion (sec)

Frequency (f) - number of cycles per unit time (Hz)

T = 1f = 1 f T

• More Characteristics of WavesCrest and Trough- the highest and lowest points from the equilibrium position

Wavelength (l) - The distance between two adjacent similar points of a periodic wave (m)

Node - Position on a standing wave that has no displacement

Antinode Position on a standing wave that is displaced to its maximum displacement

• Standing Wave when two waves traveling in opposite directions interfereThe waves must have the same f, A, and lPoints of complete constructive and destructive interference

http://www.phy.ntnu.edu.tw/~hwang/waveType/waveType.html

• Standing Waves

• How many degrees out of phase are these 2 waves?Which points are in phase?In Phase points on a wave in the same point in their cycleC and F90

• The Speed of a Wave on a string or spring

V = [F/ (m/L)]

• The Speed of a WaveV = d t

V = f l = l T

f = 1 T

The speed of sound in air is 331 m/sThe speed of light in a vacuum is 3.00 x 108 m/s = c

• *Notes from Activity: Waves and Springs

What happens to a wave form when there is a disturbance in the medium through which it is traveling???

Standing WavesWave interactionsInterference: ConstructiveDestructive

• Constructive Interference

• Destructive Interference

• Reflection of a Pulse

• SoundSound waves are __________ and ___________.Pitch - how high or low we perceive sound to be, depending on the frequency of the sound waveThe audible range for humans is 20 Hz to 20,000 Hz.Ultrasonic waves: Medical applications, animal communication, others...

Speed of sound depends on the medium in which it is traveling in. Speed generally increases with: denser phasehigher temperature

• Sound does not travel in a linear wave as we sometimes model it. It really travels in 3D.

Wave fronts - the concentric spheres of compression radiating from the source of the sound

• Doppler Effect - frequency shift that is the result of relative motion between the source of waves and an observermoving towardsf1 = f / (1 - Vs/V)moving awayf1 = f / (1 + Vs/V)f = emitted frequencyf1 = perceived frequencyV Velocity of Sound (331 m/s)Vs Relative velocity of the Source

Hear the Doppler Effect Great Physlet http://webphysics.davidson.edu/applets/applets.html

Click here to see the video of a plane breaking the sound barrier http://www.brewsterschools.org/brewster/brewsterhigh/plamoreaux/assets/sonicboom.mpg

Know Red Shift and Blue Shift

• Doppler Effect

• Intensity - rate at which energy flows through a unit area perpendicular to the direction of wave motionintensity = P = P A 4pr2Decibel Level (dB) - relative intensity of sound (logarithmic relationship)

• Natural frequency - certain frequency at which an object vibratesResonance - a condition that exists when the frequency of a force applied to a system matches the natural frequency of vibration of the system.

Disastrous effects from earthquakes or windshttp://www.regentsprep.org/Regents/physics/phys04/bresonan/default.htm

• Harmonicsfundamental frequency - the lowest frequency of vibration of a standing wave

harmonic series - series of frequencies that includes the fundamental frequency and integral multiples of the fundamental frequency (overtones)

Standing wave on a vibrating stringPipe open at both endsPipe closed at one end

• Beat - interference of waves of slightly different frequencies traveling in the same direction, perceived as a variation in loudnessinterference: constructive and destructive

f beat = (f1 - f2 ) or (f2 - f1 )

Create and Hear Beats: http://explorescience.com/activities/Activity_page.cfm?ActivityID=44

• Light waves are __________ and __________.

Electromagnetic Waves a transverse wave consistingof oscillating electricand magnetic fields at right angles toeach other

• Radio, Micro, IR, light, UV, X, GammaRange of l and f

• LightVisible Spectrum (l = 700 nm to 400 nm) 700 nm = 700 x 10-9 m = 7.00 x 10-7 m Again, a range of colors: ROY G BV

• Wave speed v = f l = d/t

For light, (c = speed of light = 3.00 x 108 m/s)

c = f l

All electromagnetic waves move at the speed of light and behave with the characteristics of light, but they can not be detected by the eye

• Light Year the distance that light travels in a year

d = V x t = 3 x 108 m/s x 1 year

now convert

3 x 108 m x 1 year x 365 days x 24 hours x 3600 s s 1 year 1 day 1 hour

d = 9.46 x 1015 m

• Luminous Flux (P) - the rate at which visible light is emitted from a source. Unit = lumen (lm) or WattIlluminance (E) - the rate at which light falls on a surfaceUnit = lux (lx) = lm/m2 or Watt/m2 or candela

E = P = P (sphere) A 4pr2

Luminous vs- IlluminatedLuminous Intesity (l) the luminuous flux that falls on an area of 1 m2 Unit candela or candle power

• LASER - a device that produces an intense, nearly parallel beam of coherent lightLight Amplification by Simulated Emission of RadiationApplications:

Diffraction - the spreading of a wave into a region behind an obstructionenergy is dispersedmay result in areas of constructive and destructive interferenceSpectral Emissions and Absorption

• Double Slit DiffractionMaxima Constructive Interferenced sin q = m lMinima Destructive Interferenced sin q = (m + ) lm = order of the maxima (0, 1, 2, 3)d = distance between slits

Single Slit Diffraction= d sin qd = width of slit

• What happens when waves interact with matter?

Reflection - the turning back of waves at the surface of a substance

angle of incidence = angle of reflectionqi = qrboth angles are relative to the normal at the point of contactvirtual image - an image formed by light rays that only appear to intersectflat mirror-

• MirrorsConvex/ConcaveVirtual/RealUpright/InvertedRadius of Curvature and Focal LengthObject and Image DistanceMagnification

• Mirrors1 + 1 = 1so si fMagnificationM = h1 = - si h so

• Mirror Notes and Equations* Given through Activity: Concave and Convex MirrorsConvex/ConcaveVirtual/RealUpright/InvertedRadius of Curvature and Focal LengthObject and Image DistanceMagnification

Great Physlethttp://www.phy.ntnu.edu.tw/java/Lens/lens_e.html

• Reflection: The color that we perceive an object to be is the color of the light which that object reflects

• LASER - a device that produces an intense, nearly parallel beam of coherent lightLight Amplification by Simulated Emission of RadiationApplications:

• Polarization: The alignment of transverse waves in such a way that their vibrations are parallel to each other-some crystals naturally polarize-polymers -double polarization-applications: reflected glare is generally horizontal

• Refraction: The bending of wave disturbance as it passes at an angle from one medium into anotherdifferent media result in different speeds of transmission

Index of Refraction (n): -ratio of speeds of lightn = c v

• The degree of refraction is determined by:Snells Lawn1 (sin q1) = n2(sin q2)

know bending towards or away

As a wave travels from a medium to another velocity and wavelength change, but frequency does not.n2 = V1 = l1n1 V2 l2

• Dispersion when white light separates into the spectrum of colors- results because different wavelengths travel at different speeds and refract differently

• Total Internal Reflection - the complete reflection of light at the boundary of two transparent media; this effect occurs when the angle of incidence exceeds the critical angle

Critical angle sin qc = nr nionly when ni > nr

• Lens - a transparent object that refracts light rays, causing them to converge or diverge to create an imageconverging lenses vs diverging lensesfocal point (f) for a lens is the image distance for an object at an infinite distancef is: + for converging, - for divergingRay Diagrams: 3 reference raysIs the Image:Real or VirtualUpright or InvertedEnlarged or Smaller

• For lenses, the distance equation is similar to that of mirrors1 + 1 = 1so si fMagnificationM = h1 = - si h so

Lenses: the eyeglasses - combinatio

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