The intensity goes up by a factor of 4 when the amplitude doubles. The shading is proportional to intensity. These stereo speakers produce both constructive interference and destructive interference in the room, a property common to the superposition of all types of waves. All these pertinent factors are included in the definition of intensity I as power per unit area:įigure 2. In both cases, changing the area the waves cover has important effects. Earthquakes spread out, so they do less damage the farther they get from the source. Sunlight, for example, can be focused to burn wood. Waves can also be concentrated or spread out. For example, the longer deep-heat ultrasound is applied, the more energy it transfers. The energy effects of a wave depend on time as well as amplitude. In fact, a wave’s energy is directly proportional to its amplitude squared because W ∝ Fx = kx 2. Because work W is related to force multiplied by distance ( Fx) and energy is put into the wave by the work done to create it, the energy in a wave is related to amplitude. The larger the displacement x, the larger the force F = kx needed to create it. More quantitatively, a wave is a displacement that is resisted by a restoring force. Large ocean breakers churn up the shore more than small ones. Loud sounds have higher pressure amplitudes and come from larger-amplitude source vibrations than soft sounds. Large-amplitude earthquakes produce large ground displacements. The amount of energy in a wave is related to its amplitude. Ultrasound is used for deep-heat treatment of muscle strains. Loud sounds pulverize nerve cells in the inner ear, causing permanent hearing loss. Earthquakes can shake whole cities to the ground, performing the work of thousands of wrecking balls. The energy of some waves can be directly observed. (credit: Petty Officer 2nd Class Candice Villarreal, U.S. The Richter scale rating of earthquakes is related to both their amplitude and the energy they carry. The destructive effect of an earthquake is palpable evidence of the energy carried in these waves.
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