Solve the problem. Round as appropriate.
-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 $5 \mathrm { ft }$ from a light is 2 foot-candles, find the intensity on a screen $15 \mathrm { ft }$ from the light.
A) $2 / 10$ foot-candle
B) $12 / 9$ foot-candles
C) $2 / 9$ foot-candle
D) 2 foot-candles

Question

Quizplus · Accepted Answer

The intensity of light varies inversely as the square of the distance, so $I_1D_1^2 = I_2D_2^2$. Given $I_1 = 2$ foot-candles at $D_1 = 5$ ft, and $D_2 = 15$ ft, solve for $I_2$: $2 \times 5^2 = I_2 \times 15^2$, resulting in $I_2 = 2/9$ foot-candle.

Solve the Problem DDD From the Source 5ft5 \mathrm { ft }5ft

Solve the Problem $D$ From the Source $5 \mathrm { ft }$