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A 25-W incandescent light bulb radiates uniformly in all directions. (a) Calculate the average intensity 2.1 m from the bulb. lavg @ 2.1 m = W/m² (b) What is the average intensity 4.5 m from the bulb? lavg @ 4.5 m = W/m²

A 25-W incandescent light bulb radiates uniformly in all directions. (a) Calculate the average intensity 2.1 m from the bulb. lavg @ 2.1 m = W/m² (b) What is the average intensity 4.5 m from the bulb? lavg @ 4.5 m = W/m²

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A 25-W incandescent light bulb radiates uniformly in all directions. (a) Calculate the average intensity 2.1 m from the bulb. lavg @ 2.1 m = W/m² (b) What is the average intensity 4.5 m from the bulb? lavg @ 4.5 m = W/m²
Transcribed Image Text:A 25-W incandescent light bulb radiates uniformly in all directions. (a) Calculate the average intensity 2.1 m from the bulb. lavg @ 2.1 m = W/m² (b) What is the average intensity 4.5 m from the bulb? lavg @ 4.5 m = W/m²
EM waves, like all other waves, are generated a source. The power of a source measures the rate that it radiates EM energy. The energy spreads outward as the wave carries it away from the source so the amount crossing a given area decreases with distance. The intensity at a given point measures the rate per unit area that EM energy is being transported to that point (i.e. received). Intensity = Source Power/Surface Area The surface area takes into account the specific details of how energy spreads outward as it radiates away from the source. A light source that radiates uniformly in all directions like the one shown in the figure is called isotropic or omni-directional. The energy is spread uniformly across spherical surfaces that are centered on the source so the intensity, , a distance, d, from an isotropic source that with power, P, is given by: Il = P 4zd² Observation Point Surface Area = 4nd²
Transcribed Image Text:EM waves, like all other waves, are generated a source. The power of a source measures the rate that it radiates EM energy. The energy spreads outward as the wave carries it away from the source so the amount crossing a given area decreases with distance. The intensity at a given point measures the rate per unit area that EM energy is being transported to that point (i.e. received). Intensity = Source Power/Surface Area The surface area takes into account the specific details of how energy spreads outward as it radiates away from the source. A light source that radiates uniformly in all directions like the one shown in the figure is called isotropic or omni-directional. The energy is spread uniformly across spherical surfaces that are centered on the source so the intensity, , a distance, d, from an isotropic source that with power, P, is given by: Il = P 4zd² Observation Point Surface Area = 4nd²
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