Mechanical Waves Types of Wave Describing Waves The
Mechanical Waves Types of Wave Describing Waves The Wave Equation
The Nature of Waves
What is a wave? A disturbance That propagates through space and time And transfers energy a. k. a. progressive wave or traveling wave
dropping a stone in the water plucking a guitar string blowing through a pipe Disturbance
An Unusual Disturbance
Types of Wave • Mechanical Waves • Produced by a disturbance • Transmitted by particles of the medium vibrating to and fro
Water (liquid) String (solid) Air (gas) Medium
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 crest trough Equilibrium position
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 wave compression rarefaction
Describing Waves Wavelength Amplitude Period Frequency Speed
Describing Waves displacement wavelength period amplitude position time
• 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 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
What is the amplitude in metres and the wavelength in metres? Displacement (m) 0. 5 Distance (m) -0. 5
For the same wave, what is the period in seconds and the frequency in Hertz? Displacement (m) 0. 5 Time (s) -0. 5 0. 2 0. 4 0. 6 0. 8 1. 0 What is the speed of this wave?
20 ms What is the time period and frequency of this wave?
1. A water wave travels through a pond with a speed of 1 ms-1 and a frequency of 5 Hz. What is the wavelength of the waves? 2. The speed of sound is 330 ms-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 6 x 10 -7 m. If its frequency is 5 x 1014 Hz what is the speed of light? 4. Red light travels at the same speed. Work out its frequency if its wavelength is 4 x 10 -7 m.
- Slides: 22