Physics Notes

1
Physics Notes

• Waves and Optics
• Chapters
• 16-17, 24-26

2

• 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

• 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/waveTyp
  e.html
• http//www.explorescience.com/activities/Activity_
  page.cfm?ActivityID50

4
Transverse Waves
5
Transverse and Longitudinal Waves
6

• 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

7

• More Characteristics of Waves
• Crest 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

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• Standing Wave when two waves traveling in
  opposite directions interfere
• The waves must have the same f, A, and l
• Points of complete constructive and destructive
  interference
• http//www.phy.ntnu.edu.tw/hwang/waveType/waveTyp
  e.html

10
Standing Waves
11
In Phase points on a wave in the same point in
their cycle
Which points are in phase?
C and F

• How many degrees out of phase are these
• 2 waves?

90
12

• The Speed of a Wave on a string or spring
• V F/ (m/L) ½

13

• The Speed of a Wave
• V d
• t
• V f l l
• 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

14

• 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

15
Constructive Interference
16
Destructive Interference
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18
Reflection of a Pulse
19

• 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
  is traveling in. Speed generally increases with
  
• denser phase
• higher temperature

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21

• 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

22

• 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.htm
  l
• Click here to see the video of a plane breaking
• the sound barrier http//www.brewsterschools.org/b
  rewster/brewsterhigh/plamoreaux/assets/sonicboom.m
  pg
• Know Red Shift and Blue Shift

23
Doppler Effect
24

• Intensity - rate at which energy flows through a
  unit area perpendicular to the direction of wave
  motion
• intensity P P
• A 4pr2
• Decibel Level (dB) - relative intensity of sound
  (logarithmic relationship)

25

• 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 winds
• http//www.regentsprep.org/Regents/physics/phys04/
  bresonan/default.htm

26

• 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

27

• Beat - interference of waves of slightly
  different frequencies traveling in the same
  direction, perceived as a variation in loudness
• interference constructive and destructive
• f beat (f1 - f2 ) or (f2 - f1 )
• Create and Hear Beats http//explorescience.com/
  activities/Activity_page.cfm?ActivityID44

28

• Light waves are __________ and __________.
• Electromagnetic Waves
• a transverse wave consisting
• of oscillating electric
• and magnetic fields
• at right angles to
• each other

29
Radio, Micro, IR, light, UV, X, Gamma Range of l
and f
30

• Light
• Visible 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

31

• 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

32

• 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

33

• 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 4pr2
• Luminous vs- Illuminated
• Luminous Intesity (l) the luminuous flux that
  falls on an area of 1 m2
• Unit candela or candle power

34

• 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

35

• Double Slit Diffraction
• Maxima Constructive Interference
• d sin q m l
• Minima Destructive Interference
• d sin q (m ½) l
• m order of the maxima (0, 1, 2, 3)
• d distance between slits
• Single Slit Diffraction
• d sin q
• d width of slit

36

37

38

• 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
• qi qr
• 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-

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• Mirrors
• Convex/Concave
• Virtual/Real
• Upright/Inverted
• Radius of Curvature and Focal Length
• Object and Image Distance
• Magnification

41

• Mirrors
• 1 1 1
• so si f
• Magnification
• M h1 - si
• h so

42

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

43

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

44

• LASER - a device that produces an intense, nearly
  parallel beam of coherent light
• Light Amplification by Simulated Emission of
  Radiation
• Applications

45

• 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

46

47

• 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
48

• The degree of refraction is determined by
• Snells Law
• n1 (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 l1
• n1 V2 l2

49

50

51

52

53
Dispersion when white light separates into the
spectrum of colors- results because different
wavelengths travel at different speeds and
refract differently
54

55

• 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
• ni
• only when ni gt nr

56

• 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

57

• For lenses, the distance equation is similar to
  that of mirrors
• 1 1 1
• so si f
• Magnification
• M h1 - si
• h so
• Lenses
• the eye
• glasses - combination of lenses

58

• Lens Power
• P 1
• f
• Unit diopter (D)