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Published byEddy Pullum Modified over 5 years ago

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Mechanical Waves Types of Wave Describing Waves The Wave Equation

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What is a wave? A disturbance That propagates through space and time And transfers energy a.k.a. progressive wave or travelling wave

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Disturbance dropping a stone in the water plucking a guitar string blowing through a pipe

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An Unusual Disturbance

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Types of Wave 1 Mechanical Wave Produced by a disturbance Transmitted by particles of the medium vibrating to and fro Examples: sound, water waves

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Types of Wave 2 Electromagnetic Wave Produced by a disturbance Does not need a medium to transmit it

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Let us concentrate on Mechanical Waves!

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Medium Water (liquid) String (solid) Air (gas)

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Transverse Waves direction of disturbance is perpendicular to the direction of travel of the wave Examples: String instruments Earthquake s-waves Light

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Diagram of a transverse wave Equilibrium position crest trough

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Longitudinal Waves direction of disturbance is parallel to the direction of travel of the wave Examples: Sound waves Ultrasound Earthquake p-waves

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Diagram of a longitudinal wave compression rarefaction

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Describing Waves Wavelength Amplitude Period Frequency Speed

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Describing Waves displacement wavelength amplitude positiontime period

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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

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Amplitude Maximum displacement of vibrating particles Unit: meter, m Symbol: A

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Period Time for one complete vibration Time corresponding to one wavelength Unit: second, s Symbol: T

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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

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Wave Speed Distance moved by any point on the wave in one second Product of wavelength and frequency Units: ms -1 Symbol: v

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Displacement (m) Distance (m) 0.5 -0.5 What is the amplitude in metres and the wavelength in metres?

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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?

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20 ms What is the period and frequency of this wave?

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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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