 # Mechanical Waves Types of Wave Describing Waves The Wave Equation.

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Mechanical Waves Types of Wave Describing Waves The Wave Equation

What is a wave? A disturbance That propagates through space and time And transfers energy a.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 Wave 2 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 wave compression rarefaction

Describing Waves Wavelength Amplitude Period Frequency Speed

Describing Waves displacement 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) 0.20.40.60.81.0 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 -7 m. If its frequency is 5x10 14 Hz what is the speed of light? 4.Red light travels at the same speed. Work out its frequency if its wavelength is 4x10 -7 m.

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