WAVE Basics

1
WAVE Basics

• Chapters 15

2
What are Waves?

• A wave is a disturbance that transmits energy
  through matter or space.

3
Types of Waves

• There are two types of waves
• Mechanical Require a medium (matter through
  which a wave travels)
• Examples Include
• Ocean waves, medium water
• Sound waves, medium air
• Seismic Waves (Earthquake), medium earth

4
Types of Waves

• Electromagnetic caused by a disturbance in
  electric and magnetic fields and do not require a
  medium.
• Examples include

5
Wave Movement

• A wave front is the front of a wave that is
  transferring energy.
• In a single system all of the wave fronts have
  the same amount of energy, but as the wave front
  spreads out, so does the energy.

6
Wave Movement

• Waves can move in two basic ways
• Transverse Motion particles of the medium
  vibrate perpendicularly to the direction the wave
  travels.
• Example light wave
• Longitudinal (Compressional) Motion particles
  of the medium vibrate parallel to the direction
  the wave travels.
• Example sound wave

7
Parts of a Wave

• You will be responsible for identifying parts of
  a wave on both a transverse and longitudinal
  wave. Complete the descriptions and label the
  following on your note outline

8
Parts of a Wave

• Transverse Wave The top of the wave is called a
  crest (peak) the bottom of the wave is called
  the trough.
• Longitudinal Wave The point of maximum
  compression is called a compression The point
  of least amount of compression is called a
  rarefaction.

Crest
Trough
Compression
Rarefaction
9
Parts of a Wave

• Wavelength (?) is the total length of 1 wave.
• In transverse waves its typically measured from
  crest to crest or trough to trough.
• In longitudinal waves its measured from
  compression to compression or rarefaction to
  rarefaction.
• The shorter the wavelength, the more energy the
  wave is carrying.

1 ?
1 ?
1 ?
1 ?
10
Parts of a Wave

• Amplitude can be measured on a transverse wave.
  It height from the resting point to the crest or
  the resting point to the trough.
• The larger the amplitude, the more energy the
  wave is carrying.

Amplitude
Amplitude
11
Wave Measurements

• A period (T) is the time it takes for one full
  wavelength of wave to pass a certain point.
• A period is a measurement of time, so its SI unit
  is seconds (s).

12
Wave Measurements

• The frequency (f) of a wave is the number of full
  wavelengths that pass a given point per second.
• The SI unit for measuring frequency is Hertz
  (Hz).

13
Wave Measurements

• The frequency (f) of a wave is the number of full
  wavelengths that pass a given point per second.
• The SI unit for measuring frequency is Hertz
  (Hz).
• Frequency is the inverse of period
• f 1 / T

14
Wave Measurements

• Wave speed (v) is the speed at which a wave
  passes through a medium and is measured using the
  following equation
• wave speed (m/s) frequency (Hz) x wavelength
  (m)
• v f x ?

15
Wave Measurements

• A wave along a guitar string has a frequency of
  440 Hz and a wavelength of 1.5 m. What is the
  speed of the wave?

v ? m/s f 440 Hz ? 1.5 m
v f ?
v 440 Hz x 1.5 m
v 660 m/s
16
Wave Measurements

• The speed of sound in air is about 340 m/s. What
  is the wavelength of sound waves produced by
  guitar strings vibrating at a frequency of 440 Hz?

v 340 m/s f 440 Hz ? ? m
? v / f
? 340 m/s / 440 Hz
? 0.77 m
17
Wave Measurements

• The speed of light is 3 x 108 m/s. What is the
  frequency of microwaves with a wavelength of 0.01
  m?

v 3 x 108 m/s 300,000,000 m/s f ? Hz ? 0.01
m
f v / ?
f 300,000,000 m/s / 0.01 m
f 30,000,000,000 Hz
18
Wave Behavior

• A reflection is the bouncing back of a wave as it
  meets a surface or a boundary.

19
Wave Behavior

• How a wave reflects depends upon the surface that
  it bounces off of.
• Example When sending pulses down a rope with a
  free end, the wave comes back normal.
• Example When sending pulses down a rope with a
  fixed end, the wave comes back inverted.

Free
Fixed
20
Wave Behavior

• Diffraction is the bending of a wave as it passes
  an edge or an opening.

21
Wave Behavior

• Refraction is the bending of waves as they pass
  from one medium to another.

22
Wave Behavior

• Interference occurs when the combination of two
  or more waves exist in the same place at the same
  time.
• Constructive interference bigger wave.
• Destructive interference smaller wave.

23
Wave Behavior

• Standing waves are caused by two identical waves
  going in opposite directions.
• Series of constructive and destructive
  interferences.
• They have regions of no vibration (nodes) and
  regions of maximum vibration (antinodes).

24
Wave Behavior

• The frequency of a wave can change when the
  source of the wave or the observer is moving.
  This is called the Doppler Effect.