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Power and Intensity

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by

Richard Datwyler

on 18 September 2015

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Transcript of Power and Intensity

Power and Intensity
This concept of power / intensity
is applicable to all types of waves
Sound
Light
E&M
The source is where the wave originates
It does so with a given amount of power
Power has units of Watts
We assume that this is a simple problem with no wave guides, and the wave propagates outward in all directions.


Think spheres.
That power must get 'shared' over the surface of the sphere as it propagates out.

As it expands, it 'spreads' that power out, making it not as Intense.
Intensity is defined this way Power / area
The surface area of a sphere is
Making the intensity equation
A 100 W light bulb is in the middle of a large theater. What is the intensity of the light when it reaches someone up in the balcony, approximately 30 m away?
What would be his distance if he wanted half that intensity?
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