2/26/2024 0 Comments Intensity of a light wave equationThe intensity of a sound wave is proportional to the square of the amplitude (pressure or velocity) and the intensity of an electromagetic wave is proportional to the square of the amplitude (electric field or magnetic field). We saw above in Power in a wave that the power transmitted is proportional to the square of the amplitude. So we can work out the power output P of the sun: The earth is 8 light minutes from the sun (another memorable quantity). This quantity is well known to those working with solar cells, although the intensity recorded at ground level is inevitably lower. Above the earth's atmosphere, the intensity provided by the sun is 1.4 kW.m −2. This is a simple example, using a radiator that is very close to isotropic: the sun. Further, measurements are usually complicated by reflections. However, this equation should be used with caution. At a distance r, all of the radiated power is radiated through a sphere with area 4πr 2. For examples, we might think of a small source of sound high up in the air, or a small lamp as a source of light. For waves in three dimensions, power is transmitted through an area, which is why we introduce the intensity I, defined as the power per unit area.įor a simple case, imagine a small source of power P, which is radiating waves isotropically, which means equally in all directions. So the kinetic energy ½ mv 2 is proportional to μA 2ω 2.įor a wave in one dimension, as seen above, power is transmitted at a point, from the continuum to the left to the continuum to the right. Remember that, for the travelling sine wave, each point on the wave executes simple harmonic motion with amplitude A and angular frequency ω. The appearance of the squared terms is logical.
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