If the distance from the x-ray tube increases, the intensity of the x-ray beam ______.

If the distance from the x-ray tube increases, the intensity of the x-ray beam ______.

• A. Increases
• B. Doubles
• C. Remains the same
• D. Decreases

Answer: (D)

Beam intensity drops with distance due to the inverse square law: intensity is proportional to 1 over the distance squared from the focal spot. When the tube is moved farther away, the same number of photons fan out over a larger area, so the energy per unit area reaching the receptor decreases. Doubling the distance reduces intensity to about one quarter; tripling it reduces to about one ninth. That’s why increasing distance decreases intensity. In practice, if you change distance in dental imaging, you’d compensate by increasing exposure parameters (within safe and diagnostic limits) to maintain adequate receptor exposure.

Beam intensity drops with distance due to the inverse square law: intensity is proportional to 1 over the distance squared from the focal spot. When the tube is moved farther away, the same number of photons fan out over a larger area, so the energy per unit area reaching the receptor decreases. Doubling the distance reduces intensity to about one quarter; tripling it reduces to about one ninth. That’s why increasing distance decreases intensity. In practice, if you change distance in dental imaging, you’d compensate by increasing exposure parameters (within safe and diagnostic limits) to maintain adequate receptor exposure.