For radiation exposure, if distance is doubled, exposure is reduced by what factor?

• A. No change
• B. 1/8
• C. 1/4
• D. 1/2

Answer: (C)

Doubling the distance from a radiation source cuts the exposure by a factor of four. This follows the inverse square law: exposure is proportional to 1 over distance squared. So going from distance d to 2d makes exposure 1/(2^2) = 1/4 of the original value. In other words, exposure becomes one quarter as large. The other options don’t fit this square-law relationship (no change would ignore the physics; half or one-eighth would require different distance changes).