Physics Notes Waves and Optics Chapters 16-17, 24-26.
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Transcript of Physics Notes Waves and Optics Chapters 16-17, 24-26.
Physics Notes
Waves and Optics
Chapters
16-17, 24-26
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
3. Transverse vs Longitudinal
Transverse – Particles or disturbance vibrate perpendicularly to the direction of energy transfer
ie. 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
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 = 1 f = 1
f T
More Characteristics of Waves
Crest and Trough- the highest and lowest points from the equilibrium position
Wavelength () - 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 interfere– The waves must have the same f, A, and – Points 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 cycle
C and F
90
The Speed of a Wave on a string or spring
V = [F/ (m/L)] ½
The Speed of a Wave
V = d t
Vf = 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 Waves
Wave interactions
Interference: Constructive
Destructive
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 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 is traveling in. Speed generally increases with: – denser phase– higher 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 observer
moving towards f1 = f / (1 - Vs/V)
moving away f1 = f / (1 + Vs/V)
f = emitted frequency
f1 = perceived frequency
V – 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 motion
intensity = P = P
A 4r2
Decibel Level (dB) - relative intensity of sound (logarithmic relationship)
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
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 of the fundamental frequency (overtones)
• Standing wave on a vibrating string
• Pipe open at both ends
• Pipe 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 consisting
of oscillating electric
and magnetic fields
at right angles to
each other
Radio, Micro, IR, light, UV, X, GammaRange of and f
Light
Visible Spectrum ( = 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 d/t
For light, (c = speed of light = 3.00 x 108 m/s)
c = f
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 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 4r2
Luminous –vs- Illuminated
Luminous 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 light
Light Amplification by Simulated Emission of Radiation
Applications:
Diffraction - the spreading of a wave into a region behind an obstruction
– energy is dispersed
– may result in areas of constructive and destructive interference
– Spectral Emissions and Absorption
Double Slit Diffraction
Maxima – Constructive Interference
d sin m Minima – Destructive Interference
d sin m + ½) m = order of the maxima (0, 1, 2, 3…)
d = distance between slits
Single Slit Diffraction
= d sin d = 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 reflection
ir
both angles are relative to the normal at the point of contact
virtual image - an image formed by light rays that only appear to intersect
flat mirror-
Mirrors
Convex/Concave
Virtual/Real
Upright/Inverted
Radius of Curvature and Focal Length
Object and Image Distance
Magnification
Mirrors
1 + 1 = 1
so si fMagnification
M = h1 = - si
h so
Mirror Notes and Equations
* Given through “Activity: Concave and Convex Mirrors”
Convex/Concave
Virtual/Real
Upright/Inverted
Radius of Curvature and Focal Length
Object and Image Distance
Magnification
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 light
Light Amplification by Simulated Emission of Radiation
Applications:
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 another
different media result in different speeds of transmission
Index of Refraction (n):
-ratio of speeds of light
n = c
v
The degree of refraction is determined by:
Snell’s Law
n1 (sin 1) = n2(sin 2)
know bending towards or away
As a wave travels from a medium to another velocity and wavelength change, but frequency does not.
n2 = V1 = 1
n1 V2 2
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 c = nr
ni
only when ni > nr
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 distance
f is: + for converging, - for diverging
Ray Diagrams: 3 reference rays
Is the Image:
Real or Virtual
Upright or Inverted
Enlarged or Smaller
For lenses, the distance equation is similar to that of mirrors
1 + 1 = 1
so si fMagnification
M = h1 = - si
h so
Lenses: • the eye• glasses - combination of lenses
Lens Power
P =1
f
Unit: diopter (D)