Notes - Unit 8 - Waves, Sound, And Light

8/9/2019 Notes - Unit 8 - Waves, Sound, And Light

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Physics Notes

Waves and Optics

Chapters16-17, 24-26


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Wave - the motion of a disturbance that transmits

energy

Comparing Types of Waves

1. Mechanical vs Electromagnetic

Mechanical - requires a medium to transfer energy

ie. slinky, water, sound, earthquake

Electromagnetic - requires no medium

ie. radio, micro, IR, visual, UV, X, gamma


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3. Transverse vs Longitudinal

Transverse Particles or disturbance vibrate

perpendicularly to the direction of energy transferie. light, slinky

Longitudinal - Particles vibrate parallel to the

direction of the energy transfer (Pressure Wave)compression vs rarefraction

ie. sound, slinky

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

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


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Transverse Waves


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Transverse and Longitudinal Waves


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Aspects of all SHM (including waves)

Amplitude (A) - maximum displacement fromequilibrium (m) Intensity or Energy

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

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

T = 1 f = 1

f T


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More Characteristics of Waves

Crest and Trough- the highest and lowest points from

the equilibrium position

Wavelength (P) - 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


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Standing Wave when two waves traveling in

opposite directions interfere

The waves must have the same f, A, and P Points of complete constructive and destructive

interference

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


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Standing Waves


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How manydegrees out of

phase are these

2 waves?

Which points

are in phase?

In Phase points on a wave in the same point in

their cycle

C and F

90


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The Speed of a Wave on a string or spring

V = [F/ (m/L)]


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The Speed of a Wave

V = d

t

V !fP = P

T

f = 1

T

The speed of sound in air is 331 m/s

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


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*Notes from Activity: Waves and Springs

What happens to a wave form when there is adisturbance in the medium through which it is

traveling???

Standing Waves

Wave interactions

Interference: ConstructiveDestructive


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Constructive Interference


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Destructive Interference


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Reflection of a Pulse


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Sound

Sound waves are __________ and ___________.

Pitch - how high or low we perceive sound to be,

depending on the frequency of the sound wave

The 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 istraveling in. Speed generally increases with:

denser phase

higher temperature


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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


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Doppler Effect - frequency shift that is the result of relative motion

between the source of waves and an observer

moving towards f1 = f / (1 - Vs/V)

moving away f1 = f / (1 + Vs/V)

f = emitted frequency

f1 = perceived frequency

V Velocity ofS

ound (33

1 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 barrierhttp://www.brewsterschools.org/brewster/brewsterhigh/plamoreaux/assets/sonicboom.mpg

Know Red Shift and Blue Shift


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Doppler Effect


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Intensity - rate at which energy flows through a unit

area perpendicular to the direction of wave motion

intensity = P = P

A 4Tr2

Decibel Level (dB) - relative intensity of sound

(logarithmic relationship)


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Natural frequency - certain frequency at which an object

vibrates

Resonance - 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


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Harmonics

fundamental frequency - the lowest frequency of

vibration of a standing wave

harmonic series - series of frequencies that includes

the fundamental frequency and integral multiples ofthe fundamental frequency (overtones)

Standing wave on a vibrating string Pipe open at both ends

Pipe closed at one end


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Beat - interference of waves of slightly differentfrequencies traveling in the same direction,perceived as a variation in loudness

interference: constructive and destructive

fbeat = (f1 - f2 ) or (f2 - f1 )

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


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Light waves are __________ and __________.

Electromagnetic Waves

a transverse wave consisting

of oscillating electric

and magnetic fields

at right angles to

each other


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Radio, Micro, IR, light, UV, X, Gamma

Range ofP and f


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Light

Visible Spectrum (P = 700 nm to 400 nm)

700 nm = 700 x 10-9 m = 7.00 x 10-7 mAgain, a range of colors: ROY G BV


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Wave speed

v = fP !d/t

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

c = fP

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


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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


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Luminous Flux (P) - the rate at which visible light is emitted

from a source.

Unit = lumen (lm) or Watt

Illuminance (E) - the rate at which light falls on a surface

Unit = lux (lx) = lm/m2 or Watt/m2 or candela

E = P = P (sphere)

A 4Tr2

Luminous vs- Illuminated

Luminous Intesity (l) the luminuous flux that falls on an area

of 1 m2

Unit candela or candle power


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LASER- a device that produces an intense, nearly

parallel beam of coherent light

LightAmplification by Simulated Emission ofRadiationApplications:

Diffraction - the spreading of a wave into a regionbehind an obstruction

energy is dispersed

may result in areas of constructive and destructiveinterference

Spectral Emissions and Absorption


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Double Slit Diffraction

Maxima Constructive Interference

d sin U!m PMinima Destructive Interference

d sin U!m + ) P

m = order of the maxima (0, 1, 2, 3)

d = distance between slits

Single Slit Diffraction

P= d sin U

d = width of slit


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What happens when waves interact with matter?

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

angle of incidence = angle of reflectionUi !Ur

both angles are relative to the normal at the point of

contactvirtual image - an image formed by light rays that only

appear to intersect

flat mirror-


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Mirrors

Convex/Concave

Virtual/RealUpright/Inverted

Radius of Curvature and Focal Length

Object and Image Distance

Magnification


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Mirrors

1 + 1 = 1

so si f

Magnification

M = h1

= - sih so


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Mirror Notes and Equations

* Given through Activity: Concave and Convex

MirrorsConvex/Concave

Virtual/Real

Upright/InvertedRadius of Curvature and Focal Length

Object and Image Distance

Magnification

Great Physlet

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


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Reflection: The color that we perceive an

object to be is the color of the light which that

object reflects


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LASER- a device that produces an intense, nearly

parallel beam of coherent light

LightAmplification by Simulated Emission ofRadiationApplications:


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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


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Refraction: The bending of wave disturbance as it

passes at an angle from one medium into another

different media result in different speeds oftransmission

Index of Refraction (n):

-ratio of speeds of light

n = c

v


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The degree of refraction is determined by:

Snells Law

n1 (sin U1) = n2(sin U2)

know bending towards or away

As a wave travels from a medium to another velocity

and wavelength change, but frequency does not.

n2 = V1 = P1

n1 V2 P2


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Di i h hit li ht t


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Dispersion when white light separates

into the spectrum of colors

- results because different wavelengthstravel at different speeds and refract

differently


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T t l I t l R fl ti th l t fl ti f


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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 Uc = nr

ni

only when ni > nr

L t t bj t th t f t li ht


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Lens - a transparent object that refracts light rays,

causing them to converge or diverge to create an

image

converging lenses vs diverging lenses

focal point (f) for a lens is the image distance for an

object at an infinite distancef is: + for converging, - for diverging

Ray Diagrams: 3 reference rays

Is the Image:Real or Virtual

Upright or Inverted

Enlarged orSmaller

For lenses the distance equation is similar to that of


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For lenses, the distance equation is similar to that ofmirrors

1 + 1 = 1so si f

Magnification

M = h1 = - sih so

Lenses:

the eye

glasses - combination of lenses

L P


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Lens Power

P =1f

Unit: diopter (D)

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Notes - Unit 8 - Waves, Sound, And Light