How Far Should the 70-cd Lamp Be to Match the 10-cd Lamp's Intensity?

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SUMMARY

The discussion centers on calculating the distance from a wall for a 70-cd lamp to match the intensity of a 10-cd lamp positioned 8.0 meters away. The key principle is that light intensity diminishes with the square of the distance, described by the equation I = P/(4πr²), where I is intensity, P is power, and r is distance. By applying this inverse square law, the distance for the 70-cd lamp can be determined to ensure equal intensity on the wall.

PREREQUISITES
  • Understanding of light intensity and the candela unit
  • Familiarity with the inverse square law of light
  • Basic algebra for solving equations
  • Knowledge of point source light behavior
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  • Learn how to apply the equation I = P/(4πr²) in practical scenarios
  • Explore the concept of luminous intensity and its measurement
  • Investigate real-world applications of light intensity calculations
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Homework Statement


A 10-cd point source lamp and a 70-cd point source lamp cast equal intensities on a wall. If the 10-cd lamp is 8.0 m from the wall, how far from the wall is the 70-cd lamp?



Homework Equations


I'm not sure what the equation for a candela is.


The Attempt at a Solution


Can't attempt it without knowing an equation.


That's the only information given, and I don't know how to form an equation.
 
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A candela is a unit of intensity for light. And you remember that intensity falls off as 1/r^2.
 

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