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

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AI Thread Summary
To determine the distance of the 70-cd lamp from the wall to match the intensity of the 10-cd lamp, the inverse square law of light intensity, which states that intensity decreases with the square of the distance (1/r^2), is essential. Given that the 10-cd lamp is 8.0 m away from the wall, the intensity of both lamps must be equal at that point. The relationship between the two lamps can be expressed as I1/I2 = (d2^2)/(d1^2), where I represents intensity and d represents distance. By applying this formula, the distance of the 70-cd lamp can be calculated. Understanding the candela as a unit of light intensity is crucial for solving this problem.
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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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