Unit 10Waves & Wave Properties

Introduction to Wave Properties

A wave is … …a motion of

disturbance

Waves “propagate in 3-dimensions”.

Waves move through a medium – the particles do not MOVE WITH THE WAVE!

A wave moves through the medium.The medium does not move WITH the wave motion.The particles in the medium vibrate!

http://www.youtube.com/watch?v=bEfrtAOMuvk

(1:26)

General Wave Formcrest

trough

Equilibrium Line

There are 2 types of waves

Transverse Wave Longitudinal Wave

Particle vibration is perpendicular to wave motion

Particle vibration is parallel to wave motion

Transverse Wave

Particle vibration is perpendicular to wave motion

• http://www.acoustics.salford.ac.uk/feschools/waves/bungyvideo.htm

• http://www.acoustics.salford.ac.uk/feschools/waves/guitarvideo.htm

Slow Motion Video of “Transverse Wave”

Longitudinal Wave

Particle vibration is parallel to wave motion

Slow Motion Video of “Longitudinal Wave”

http://www.acoustics.salford.ac.uk/feschools/waves/slinkyvideo.htm

Label the following examples as transverse or longitudinal waves.

transverse

longitudinal

Waves move through the medium!

• The wave only __________________ the particle,• the particle does not __________ with the wave.

vibratesmove

There are 2 Categories of Waves

Mechanical Waves

Electromagnetic Waves

Need a medium to travel through.

Can travel without a medium

For example, through gas, liquid or solids

For example, through a vacuum

Sounds waves are…

Mechanical waves!

And an example of a longitudinal wave!

Light waves are

Electromagnetic WavesAnd an example of a

transverse wave.

Wave Speed EquationV=f λ

velocity = frequency x wavelength

c =f λSpeed of light = frequency x wavelength

Sound needs a medium to travelSpeed of Sound in standard air:

Light can travel through a vacuumSpeed of Light in a vacuum:

v = 340 m/s

c = 300,000,000m/s

Frequency, Wavelength & Speed

Which wave has the lower frequency? Which wave has the higher frequency?Which wave has the lower speed?

Lower frequency

Higher frequency

Same Speed!

Which wave has the higher frequency? Which wave has the higher wavelength?Which wave has the higher speed?

higher frequency

higher wavelength

Same speed!

What is the relationship between speed, frequency and wavelength?

• The only way to change the speed of the wave is to _______________________.

• A change in the frequency will change _____________.

• A change in the wavelength will change ___________.

To change the medium

wavelength

frequency

Interference“The Superposition Principal”

Show resultant wave and label each as constructive or destructive interference.

Complete destructive interferenceConstructive interference

Destructive interference

Which Wave is the Resultant Wave?

This is the resultant wave!

Which Wave is the Resultant Wave?

Waves can “Reflect”Reflection occurs for both mechanical and electromagnetic waves. Sound and light waves can both reflect, but do so with various rules which will later be discussed with examples.Below are two common examples of sound and light reflecting.

Sound waves can reflect causing what we know as an echo.

Light waves can reflect causing what we know as a mirror effect.

Standing WavesA wave pattern that results when two waves of the same frequency, wavelength and amplitude travel in opposite directions and interfere.

Standing Waves have ‘nodes’ and ‘antinodes’

Antinode:A point in a standing wave which has the maximum amplitude.

Node:A point in a standing wave which has no amplitude.

How many nodes and antinodes are in each standing wave?

2 nodes, 1 antinode

3 nodes, 2 antinodes

4 nodes, 3 antinodes

Create a Standing Wave!

The Doppler Effect• An apparent change in frequency due to relative

motion.

– Examples:• Car music/horn as it drives by• Police sirens• Sonic Boom! (Breaking the sound barrier)• Red shift and blue shift with light waves

High frequency

Low frequency

http://youtu.be/h4OnBYrbCjY(0-1min)

The Doppler Effect

Small apparent wavelengthHigh Frequency wave

Large apparent wavelengthLow Frequency wave