Calculating Intensity of 13-Watt Bulb at 1.2m Distance

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To calculate the intensity of a 13-watt bulb at a distance of 1.2 meters, consider the bulb as a point source emitting light uniformly in all directions. The total power of the bulb is 13 watts, and the area over which this power spreads can be determined by the surface area of a sphere with a radius of 1.2 meters, calculated using the formula 4πr². This results in an area of approximately 15.1 m². The intensity, or power per unit area, is then found by dividing the total power by the surface area, yielding an intensity of about 0.86 W/m². Understanding these principles is essential for solving similar problems in physics.
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Homework Statement


A low energy, 13-watt bulb illuminates your desk from a distance of 1.2m. You can assume that it acts as a point source and that it is 100% efficient. What is the intensity (power per unit area) at the desk (in Wmˉ²)?

Homework Equations


Velocity = Frequency * Wavelength
Intensity is proportional to amplilude²

The Attempt at a Solution


I don't know how to start!
 
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Imagine the bulb as a point source sending out its energy equally in all directions. By the time the light has traveled 1.2 m, over how large an area is the total power spread? Hint: What's the area of a sphere of that radius?
 

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