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a wave is formed when some disturbance is created in the medium . types of waves: mechanical wave & electromagnetic wave
form of mechanical wave: I) longitudinal II) transverse .S.I. unit is meter 'm ' .

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Wave is defined as the movement of any periodic motion like a spring, a pendulum, a water wave, an electric wave, a sound wave, a light wave, etc. A wave is a form of disturbance created by the medium. it's SI unit is metre(m).