mechanical waves types of wave describing waves the wave equation
TRANSCRIPT
Mechanical WavesTypes of Wave
Describing WavesThe Wave Equation
What is a wave?
A disturbanceThat propagates through space and timeAnd transfers energya.k.a. progressive wave or travelling wave
Disturbance
dropping a stone in the water
plucking a guitar string
blowing through a pipe
An Unusual Disturbance
Types of Wave
1 Mechanical Wave• Produced by a disturbance• Transmitted by particles of the medium vibrating to and fro
• Examples: sound, water waves
Types of Wave2 Electromagnetic Wave
• Produced by a disturbance• Does not need a medium to
transmit it
Let us concentrate on Mechanical Waves!
Medium
Water (liquid)
String (solid)
Air (gas)
Transverse Waves
• direction of disturbance is perpendicular to the direction of travel of the wave
• Examples: • String instruments• Earthquake s-waves• Light
Diagram of a transverse wave
Equilibrium position
crest
trough
Longitudinal Waves• direction of disturbance is parallel to the
direction of travel of the wave• Examples:
• Sound waves• Ultrasound• Earthquake p-waves
Diagram of a longitudinal wavecompression
rarefaction
Describing Waves
WavelengthAmplitudePeriodFrequencySpeed
Describing Wavesdi
spla
cem
ent
wavelength
amplitude
positiontime
period
• Wavelength• Equivalent to one complete vibration• Distance from crest to crest, or trough
to trough, OR• Distance from two identical successive
points on a graph• Unit: meter, m• Symbol: lambda, λ
• Amplitude• Maximum displacement of vibrating
particles• Unit: meter, m• Symbol: A
• Period• Time for one complete vibration• Time corresponding to one wavelength• Unit: second, s• Symbol: T
• Frequency• Number of vibrations (or waves) in one
second• Reciprocal of period, 1/T• Units:
• vibrations per second, s-1• cycles per second, s-1•Hertz, Hz
• Symbol: ƒ
Wave Speed•Distance moved by any point on the wave in one second•Product of wavelength and frequency•Units: ms-1
•Symbol: v
Displacement (m)
Distance (m)
0.5
-0.5
What is the amplitude in metres and the wavelength in metres?
Displacement (m)
Time (s)
0.2 0.4 0.6 0.8 1.0
0.5
-0.5
For the same wave, what is the period in seconds and the frequency in Hertz?
What is the speed of this wave?
20 ms
What is the period and frequency of this wave?
1. A water wave travels through a pond with a speed of 1ms-1 and a frequency of 5Hz. What is the wavelength of the waves?
2. The speed of sound is 330ms-1 (in air). When Ricky hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound?
3. Purple light has a wavelength of around 6x10-7m. If its frequency is 5x1014 Hz what is the speed of light?
4. Red light travels at the same speed. Work out its frequency if its wavelength is 4x10-7m.