How does the inverse square law affect exposure with distance, and what is the correct formula?

How does the inverse square law affect exposure with distance, and what is the correct formula?

• A. Exposure rate is proportional to distance; I2 = I1 × (d2/d1)^2.
• B. Exposure rate is proportional to 1/distance squared; I2 = I1 × (d1/d2)^2.
• C. Exposure rate increases with distance; I2 = I1 × (d1/d2)^3.
• D. Exposure rate is independent of distance.

Answer: (C)