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Published byDesmond Grundy Modified over 2 years ago

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Representing waves

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There are two ways we can represent a wave in a graph;

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Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s displacement cm

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Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s displacement cm PERIOD

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Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s displacement cm PERIOD

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Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s displacement cm PERIOD IMPORTANT NOTE: This wave could be either transverse or longitudnal

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Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm displacement cm

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Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm displacement cm WAVELENGTH

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Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm displacement cm WAVELENGTH

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Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm displacement cm WAVELENGTH IMPORTANT NOTE: This wave could also be either transverse or longitudnal

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Wave intensity

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This is defined as the amount of energy per unit time flowing through unit area It is normally measured in W.m -2

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Wave intensity For example, imagine a window with an area of 1m 2. If one joule of light energy flows through that window every second we say the light intensity is 1 W.m -2.

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Intensity at a distance from a light source I = P/4πd 2 where d is the distance from the light source (in m) and P is the power of the light source(in W)

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Intensity at a distance from a light source I = P/4πd 2 d

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Sound intensity The lowest intensity that can normally be heard by a human ear is 1 x W.m -2 This is a sound intensity level of 0 dB

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Intensity and amplitude

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The intensity of a wave is proportional to the square of its amplitude I α a 2 (or I = ka 2 )

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Intensity and amplitude This means if you double the amplitude of a wave, its intensity quadruples! I = ka 2 If amplitude = 2a, new intensity = k(2a) 2 new intensity = 4ka 2

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Surfers know this!

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Let’s try some more questions!

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