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Chapter 14: Problem 9

The intensity of light from a localized source decreases as the inverse square of the distance from the source. Does this mean that the light loses energy as it propagates?

Short Answer

Expert verified
No, the light does not lose energy as it propagates from its source. The decrease in intensity is due to the spreading out of the same amount of energy over a larger area as we move further from the source.

Step by step solution

01

Understand the Relationship

First, it's crucial to comprehend that Light propagates as spherical waves out of its source. The intensity of the light source is not dependent on its distance from the source but in how it is spread out in the space. When the light source is close, its intensity is concentrated in a small sphere, and as you move away, the same energy is distributed over a larger sphere causing the intensity to decrease.
02

Understanding Energy Conservation

The energy of the light doesn't decrease as it propagates away from its source. Rather, it remains constant. However, since the same energy is spreading over a growing spherical surface, the energy density (also perceived as intensity) reduces. In the core principle, this is just conservation of energy.

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