# Waves & Energy Transfer

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Waves & Energy Transfer
Chapter 14

14.1 Wave Properties Energy 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 Junction of two springs is a boundary between two media.

A pulse reaching boundary (a) is partially reflected & partially transmitted. (free)
Fig 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 338 Continuous waves – from a region of higher speed to one with lower speed. Fig

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

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 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 Diffraction bending of waves around barrier. Fig & Fig

Bibliography 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

Nodes & Antinodes

Standing Wave

Diffraction