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Oscillations and Waves Wave Characteristics

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Progressive Waves Any wave that moves through or across a medium (e.g. water or even a vacuum) carrying energy away from its source is a progressive (travelling) wave. E.g. A duck on water: As the wave passes the duck, the water (and duck) only oscillate vertically. Wave direction Duck oscillation

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This illustrates that there is no net transfer of the medium through which the wave travels, only energy moves from place to place. In many examples, the wave carrying medium will oscillate with simple harmonic motion (i.e. a -x).

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Types of Wave Waves can be described as transverse or longitudinal. In a transverse wave the vibration (oscillation) of particles is at right angles to the direction of energy transfer. Transverse waves cannot move through a gas. Examples: In a longitudinal wave the vibration of particles is in the same plane as the direction of energy transfer. Examples:

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Oscillation Energy transfer Transverse: Longitudinal: Energy Transfer (Label a crest (peak), trough, rarefaction, compression)

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Describing Waves Crest and trough: Points on the wave where particles are oscillating at maximum positive and negative displacement. Rarefaction and compression: Areas in a longitudinal wave where particles are far apart (lower than normal density) and close together (higher than normal density).

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Wave graphs Waves can be represented graphically in two ways: 1. Displacement - Distance: 1. Displacement – Time: Wavelength Amplitude Distance Displacement Time Period Amplitude Time Displacement

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The following terms and descriptions are mixed up: Intensity of a wave is the ‘power per unit area’ incident upon a surface, in Wm -2. (It is proportional to the square of the amplitude, so I A 2 ) TermDescription 1. Wavelength ( λ )a. The maximum displacement from the equilibrium position (in metres, m) 2. Amplitude (A)b. The distance moved by a wave crest per second (in metres per second, ms -1 ) 3. Frequency (f)c. The time required for the wave to complete one oscillation (in seconds, s) 4. Periodic Time (T)d. The distance between two successive crests (in metres, m) 5. Speed (v)e. The number of waves completed in one second (in Hertz, Hz) TermDescription 1. Wavelength ( λ )d. The distance between two successive crests (in metres, m) 2. Amplitude (A) 3. Frequency (f) 4. Periodic Time (T) 5. Speed (v) TermDescription 1. Wavelength ( λ )d. The distance between two successive crests (in metres, m) 2. Amplitude (A)a. The maximum displacement from the equilibrium position (in metres, m) 3. Frequency (f) 4. Periodic Time (T) 5. Speed (v) TermDescription 1. Wavelength ( λ )d. The distance between two successive crests (in metres, m) 2. Amplitude (A)a. The maximum displacement from the equilibrium position (in metres, m) 3. Frequency (f)e. The number of waves completed in one second (in Hertz, Hz) 4. Periodic Time (T) 5. Speed (v) TermDescription 1. Wavelength ( λ )d. The distance between two successive crests (in metres, m) 2. Amplitude (A)a. The maximum displacement from the equilibrium position (in metres, m) 3. Frequency (f)e. The number of waves completed in one second (in Hertz, Hz) 4. Periodic Time (T)c. The time required for the wave to complete one oscillation (in seconds, s) 5. Speed (v) TermDescription 1. Wavelength ( λ )d. The distance between two successive crests (in metres, m) 2. Amplitude (A)a. The maximum displacement from the equilibrium position (in metres, m) 3. Frequency (f)e. The number of waves completed in one second (in Hertz, Hz) 4. Periodic Time (T)c. The time required for the wave to complete one oscillation (in seconds, s) 5. Speed (v)b. The distance moved by a wave crest per second (in metres per second, ms -1 )

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The Wave Equation In a time of one full period (t = T), a point in a wave will move forward through one a distance of one whole wavelength (d = λ). so… substituting gives… This is called the ‘wave equation’ Speed = Distance Time Wave speed = Wavelength Time period v = λ T but… T = 1 f v = f λ

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Electromagnetic Waves The visible spectrum of light (Roy G Biv) is just a small part of a larger group of electromagnetic waves known as the ‘electromagnetic spectrum’. All electromagnetic radiation: exists as variations in electrical and magnetic fields travels at 3 x 10 8 ms -1 (300 000 000 ms -1 ) can travel through a vacuum carries energy has wave behaviour (obeying v = fλ)

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