Ch. 25: Waves

A WAVE is a rhythmic disturbance that carries

energy through matter or space

General Wave Characteristics

• Not all waves travel through a medium.

• Mechanical waves only transfer energy through matter.

• There are two types:• Transverse• Longitudinal (or compressional)

• Wave motion transfers energy without transferring matter

• Click here for a visual of mechanical waves (at bottom of page)

Mechanical Waves

Transverse Waves: matter in the medium moves perpendicular to direction the wave travels

Longitudinal (Compressional) Waves: matter in the medium moves parallel to the direction the wave travels

Combination Waves: Ocean WaterAn ocean wave is

a combination of transverse and

longitudinal waves.

The individual particles move in

ellipses as the wave disturbance moves toward the shore.

Concept Check

1. What is a wave?2. What are the two types of

mechanical waves?

Wave PropertiesThere are four wave properties:

• Amplitude• Frequency

• Wavelength• Wave Velocity

Amplitude is a measure of the amount of energy in a wave

In Compressional Waves… look at how dense the compressions are. The more dense, the higher the amplitude

In Transverse

Waves…

Frequency is the number of wavelengths that pass a fixed point each second

f = waves/secondSI unit = Hertz (Hz)As Frequency , WavelengthIs this a high- or low-frequency

wave?

Wavelength is the distance between a point on one wave and the identical point on the next wave

Calculating Frequency

F = 1/T Remember T…

Called “period” The time it takes for one wave to pass a

given point Measured in seconds

What is the frequency of ocean waves that wash up on the shore every 2.5 seconds?

Wave Velocity is how “fast” the wave moves

Velocity = wavelength x frequencyv = λfv = velocity

(m/s)λ = wavelength

(m)f = frequency

(Hz)

ExampleA sound wave travels from a speaker to your ear. If it has a frequency of 12,000 Hz and a wavelength of 2 cm, what is its velocity?

Concept Check

List and describe the four wave properties.

How do waves differ from one another?1) Energy, 2) Velocity, 3) Appearance

TRANSVERSE

COMPRESSIONAL

VS.

Some other terms to know… Period

Time for one wave to pass a given point (seconds)

Inverse of frequency Node

The point where the medium is never displaced

On the “normal” line Antinode –

The point of maximum displacement Occurs at the wave’s crest

Standing Waves

NODES

ANTINODES

Wave Behavior

All waves of all types exhibit these four behaviors: Reflection Refraction Diffraction Interference

Reflection

The “bouncing back” of a wave

The Law of Reflection says…

Angle of Incidence = Angle of Reflection

Refraction The change in wave

direction at the boundary between two different media

Different materials allow waves to travel at different speeds

Angle of Refraction Amount of bending Depends on how much

the material changes the wave’s speed

DiffractionThe bending of a wave around a barrier or a small

opening

It’s the same process for sound AND light

Interference When two or more waves (blue and red) exist in the same medium, each wave moves as though the other were absentWhen they meet, they interfere with one another and make a new wave (green).

Visualization of Interference

Constructive or Destructive? Constructive Interference – 2

waves combine to form a new wave with a larger amplitude.

Destructive Interference – 2 waves combine to produce a wave with a smaller amplitude.

Wave Formulas f = 1/T

f = frequency (Hz) T = period (s)

v = λ f v = velocity

(m/s) λ = wavelength

(m) f = frequency

(Hz)