WAVESWAVES

AS 2.3: Demonstrate an AS 2.3: Demonstrate an understanding of wave understanding of wave

phenomenon.phenomenon.

Wave MotionWave Motion

• Waves move energy and information Waves move energy and information around without moving mass.around without moving mass.

• Waves can be Waves can be mechanicalmechanical or or electromagnetic.electromagnetic.

• Waves can be Waves can be transversetransverse or or longitudinal.longitudinal.

• Waves can be Waves can be movingmoving or or stationary.stationary.

Mechanical WavesMechanical Waves

• Mechanical wavesMechanical waves consist of vibrating consist of vibrating particles called the particles called the medium.medium. The speed The speed of a mechanical wave depends on the of a mechanical wave depends on the medium. E.g. Sound waves travel faster medium. E.g. Sound waves travel faster in water than in air.in water than in air.

• Examples of mechanical waves include:Examples of mechanical waves include:

Sound waves, water waves.Sound waves, water waves.

Electromagnetic WavesElectromagnetic Waves• Electromagnetic waves require no medium Electromagnetic waves require no medium

at all. These waves consist of vibrating at all. These waves consist of vibrating energy fields. energy fields.

• They all travel at the same speed: the They all travel at the same speed: the speed of light, c = 3x10speed of light, c = 3x1088 ms ms-1-1

• Examples include:Examples include:

Transverse WavesTransverse Waves

• The particles oscillate (move back and The particles oscillate (move back and forth) perpendicular to the direction of forth) perpendicular to the direction of the wave. E.g. water waves.the wave. E.g. water waves.

Longitudinal WavesLongitudinal Waves

• The particles oscillate in the direction The particles oscillate in the direction that the wave is travelling. E.g. sound that the wave is travelling. E.g. sound waves.waves.

Demonstration

The air particles oscillate side to side – the same direction the wave is traveling.

The Slinky ExperimentThe Slinky Experiment

Waves TerminologyWaves Terminology

fT

1

Frequency appletE.g. f = 50Hz What is T?E.g. f = 50Hz What is T?

Frequency (f) = number of waves Frequency (f) = number of waves each second. E.g. 3 Hz means 3 each second. E.g. 3 Hz means 3 waves per second. waves per second.

The units for frequency are Hertz The units for frequency are Hertz (Hz).(Hz).

T is the period, the time for one T is the period, the time for one wave. (s)wave. (s)

Waves TerminologyWaves Terminology

• Amplitude (A) is Amplitude (A) is the size of the the size of the wave:wave:

• The wavelength The wavelength is is the distance from the distance from crest to crest or from crest to crest or from trough to trough:trough to trough:

λλ AppletApplet

The wave equationThe wave equation

• The velocity of a wave is The velocity of a wave is given by the formula:given by the formula: fv

V = velocity (ms-

1)

f = frequency (Hz)

= wavelength (m)

Example: Shaking the slinky 3 times per second. The waves are measured to be 0.8m.

Find: (a) The period of the wave.

(b) The speed of the wave.Wave equation applet

Water WavesWater Waves

• Waves are reflected off barriers, obeying Waves are reflected off barriers, obeying the same laws of reflection as light.the same laws of reflection as light.