Solve the variation problem.
-The intensity I of light varies inversely as the square of the distance D from the source. If the intensity of illumination on a screen 5 feet from a light is 3 foot candles, find the intensity on a screen 20 ft from the light.
A) $\frac { 3 } { 16 }$ foot-candles
B) $\frac { 3 } { 17 }$ foot-candles
C) 2 foot-candles
D) $1 \frac { 3 } { 16 }$ foot-candles

Question

Solve the variation problem.
-The intensity I of light varies inversely as the square of the distance D from the source. If the intensity of illumination on a screen 5 feet from a light is 3 foot candles, find the intensity on a screen 20 ft from the light. 
A) $\frac { 3 } { 16 }$ foot-candles
B) $\frac { 3 } { 17 }$ foot-candles
C) 2 foot-candles
D) $1 \frac { 3 } { 16 }$ foot-candles

Quizplus · Accepted Answer

The intensity of light varies inversely as the square of the distance, so $I = \frac{k}{D^2}$, where $k$ is a constant. Given $I = 3$ foot-candles at $D = 5$ feet, we find $k = 3 \times 5^2 = 75$. For $D = 20$ feet, $I = \frac{75}{20^2} = \frac{75}{400} = \frac{3}{16}$ foot-candles.

Solve the Variation Problem 316\frac { 3 } { 16 }163​

Solve the Variation Problem $\frac { 3 } { 16 }$