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Waves & Energy Transfer
Chapter 14
14.1 Wave PropertiesEnergy can be transferred by
particles or by waves. Types of Waves - Mechanical,
Electromagnetic, & Matter Mechanical waves require
medium to travel, such as air, water, & springs or ropes.
EM waves do not require medium. Ex: light waves, radio waves & x-rays. They all travel at speed of light (c). Matter waves involve electrons &
other particles that demonstrate wave like properties under certain conditions.
Will be studied under Quantum Mechanics.
Three types of mechanical waves. Transverse - particles vibrate
perpendicularly to direction of motion of wave.
Longitudinal - particles travel in direction of wave.
Surface - mixture of transverse & longitudinal.
Transverse waves do not travel through earth’s center, which indicates center is fluid.
Wave pulse - a single disturbance travels through medium.
Wave train or traveling wave - a series of pulses at regular interval.
Two Types of Waves
Measuring a Wave Period, - time required for
motion to repeat itself. Frequency, f - number of
complete vibrations per second. f = 1 /
Wavelength, - distance from crest to crest or trough to trough.
Crests - high points of wave Trough - low points of wave When time interval is one period,
wave would move a distance of 1 wavelength.
Velocity - given by v = / T or v = f
Amplitude - maximum displacement from rest or equilibrium position.
Speed of sound in air depends on temperature.
Speed of light is always constant.
3.00E8 m/s = c Ex. Prob 333 Prac Prob 335
14.2 Wave Behavior -Boundaries When wave reaches boundary of
media, it may be reflected or pass. Speed & change when wave enters
new medium. Fig 14-7 336 Junction of two springs is a
boundary between two media.
A pulse reaching boundary (a) is partially reflected & partially transmitted. (free)
Fig 14-8 337 A pulse is shown as it approaches a rigid wall (a) & as it is reflected from wall (b).
Notice amplitude is almost same but reflected pulse is inverted.
When medium changes, wave energy is both reflected & transmitted.
Waves passing from one medium to another have same f.
The change depends on v change so that f = v/ is constant.
Prac Prob 337
Wave Boundaries
Less to More More to less
Superposition of Waves Principle of superposition -
displacement of a medium caused by two or more waves is algebraic sum of displacements caused by individual waves.
Interference - result of superposition.
Destructive interference occurs when crest meets trough.
Resultant wave is smaller. Fig 14-11a 338
Constructive interference occurs when waves meet crest to crest or trough to trough.
Resultant wave is larger. Fig 14-11b 338
If waves are opposite & equal magnitude, result is 0.
Fig 14-11c 338Continuous waves – from a
region of higher speed to one with lower speed.
Fig 14-12 339
Standing Waves Node - pt that is undisturbed. Medium is not displaced as waves
pass. Antinode - pt of max displacement. Standing wave has stationary nodes &
antinodes. It is result of identical waves traveling
in opposite directions. Fig 14 -13 340
Waves in Two Dimensions Law of reflection - angle at which a
wave approaches a barrier is equal to angle at which it is reflected.
Fig 14-14 341 Normal - to barrier. Angle of incidence - angle
between incident ray & normal.
Angle of reflection - angle between normal & reflected ray.
Refraction - change of wave direction at boundary between two media.
Fig 14-15 342 Diffraction bending of waves around
barrier. Fig 14-16 342 & Fig 14-17 343
Bibliography
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/waves/em.html
http://www.glenbrook.k12.il.us/gbssci/phys/Class/waves/u10l1c.html
http://surendranath.tripod.com/Applets/Waves/Twave01/Twave01Applet.html
http://www.glenbrook.k12.il.us/gbssci/phys/Class/waves/u10l1c.html
Physics: Principles and Problems, Glencoe Digital Curriculum
Longitudinal or Compression
Light Propagation
Wavelength
Fixed Boundary
Free End
Interference
Less to More Dense
Longitudinal
Transverse
Surface Waves or Water Waves
Destructive & Constructive
Standing Wave
Diffraction
