Calculating Intensity of 13-Watt Bulb at 1.2m Distance

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SUMMARY

The discussion focuses on calculating the intensity of a 13-watt bulb at a distance of 1.2 meters, treating the bulb as a point source. The intensity is defined as power per unit area, and since the bulb is 100% efficient, all 13 watts are utilized. To find the intensity, one must calculate the surface area of a sphere with a radius of 1.2 meters, which is essential for determining how the power is distributed over that area.

PREREQUISITES
  • Understanding of point source light behavior
  • Knowledge of the formula for the surface area of a sphere
  • Familiarity with the concept of intensity as power per unit area
  • Basic grasp of physics equations related to light and energy
NEXT STEPS
  • Calculate the surface area of a sphere with a radius of 1.2 meters
  • Determine the intensity using the formula: Intensity = Power / Area
  • Explore the relationship between intensity and distance from a point source
  • Investigate the effects of bulb efficiency on light intensity calculations
USEFUL FOR

Students in physics, educators teaching light and energy concepts, and anyone interested in practical applications of intensity calculations in lighting scenarios.

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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!
 
Physics news on Phys.org
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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