Waves

What is a Waves? A wave is a disturbance

that transfers energy through matter or space.

When waves move through matter, we call the matter a medium. A medium can be solid, liquid, or gas.

Transverse waves can move through empty space without a medium.

When energy waves move through a medium, the medium stays in the same place.

In the ocean, when a wave passes, the water molecules move only in small circles!

Types of Waves : Transverse

A wave in which the medium moves at right angles to the direction of the wave is a transverse wave.

Ocean waves and light waves are transverse.

Parts of a Transverse Wave• The crest is the

highest point of a transverse wave, and the trough is its lowest point.

• One wavelength includes one complete crest plus one complete trough

• The amplitude of a transverse wave in the distance from the normal to a crest or from the normal to a trough.

• The more energy a wave has, the greater the amplitude

Types of waves: longitudinal

A longitudinal wave has the medium move parallel to the direction of the wave.

Unlike transverse waves which can travel in empty space a longitudinal waves must have a medium to travel through.

Sound travels in longitudinal waves.

Because sound is a longitudinal wave , sound will not travel in empty space.

Parts of a Longitudinal Wave• The part of a

longitudinal wave where the particles of the medium are close together is a compression.

• The part of a longitudinal wave where the particles of the medium are far apart is a rarefaction.

• One wavelength includes one complete compression plus one complete rarefaction.

Wave properties When you talk about

a “big wave,” you are describing the wave’s amplitude.

If you describe how many waves pass in a given time, you are describing the wave’s frequency.

For a transverse wave, the distance from crest to crest or trough to trough is a wavelength.

For a longitudinal wave, a wavelength is the distance between compressions or between rarefactions.It is measured in meters.

amplitude

wavelength rarefaction

compression

wavelength

Wave amplitude If you are observing

transverse waves, the amplitude is the vertical distance from the line of origin and the crest OR the line of origin and the trough.

As you increase a wave’s energy, its amplitude also increases.

Low amplitude

High amplitude

Wave frequency

The frequency of a wave is the number of waves that pass a point in a given time.

Low frequency

The unit for frequency is the Hertz, which means waves per second.

High frequency

Wave speed Wave speed measures how fast a wave is

moving toward you. Wave speed = frequency x wavelength The unit used to measure wave speed is

meters per second.

Math Problems with Waves

• Speed = frequency x wavelength

Speed

Freq. wavelength

Complete the practice problems

Wave interactions: Energy and change

When a wave interacts with another wave or with an object, the amount of energy in the wave changes.

The change in energy affects the wave’s properties.

Wave properties include, its amplitude, speed, frequency or wavelength which may change.

Wave interactions affect all wave types.

Other changes that may happen are a change in wave direction, or the wave may break apart and then re-form.

Wave interactions: wave reflection

Reflection happens when a wave bounces off of a surface.

The angle of the incoming (incident) wave equals the angle of the outgoing (reflected) wave.

incident wave

Angle of incidence

Normal

reflected wave

Angle of reflection

This is called the Law of Reflection

Wave Interactions Refraction• Waves can

change speed when they pass from one medium to another.

• Sounds travel fastest in solids and slower in air.

• Sound is slowest in mediums like air and does not travel in a vacuum.

• Light travels fastest in a vacuum, gas, and even slower through a liquid, and even slowest through a solid like glass.

• Refraction is the bending of a wave as it passes through a medium.

Wave interactions: refraction Pt2

Wave interactions: diffraction

The bending of a wave as it contacts the edge of a barrier is called diffraction.

When waves are diffracted at the edge of a barrier, their wavelengths and frequencies do not change.

outgoing wave crests

Incoming wave crests

Diffraction allows you to hear around corners and diffraction glasses split light into colors of the rainbow

Wave interactions: interference

The effect of two or more interacting waves is interference.

There are 2 types of interference constructive and destructive.

When two crests meet, the result is a larger wave. This is constructive interference. A tidal wave such as a tsunami is caused by constructive interference ! ! !

Constructive Interference

• When a crest and a trough meet, the result is a smaller wave. This is destructive interference.

• In some auditoriums destructive interference makes it difficult to hear what is on stage.

Destructive Interference