If you double the distance from a ultraviolet source, the intensity becomes one quarter of its original value.

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Prepare for the REMBE Electrotherapy Test. Study with flashcards and multiple choice questions. Each question comes with hints and explanations. Master electrotherapy concepts and get ready for your exam!

Multiple Choice

If you double the distance from a ultraviolet source, the intensity becomes one quarter of its original value.

Explanation:
The intensity from a point ultraviolet source follows the inverse-square law: it decreases with the square of the distance. When you double the distance, the same power spreads over a surface four times larger, so the energy per unit area drops to one quarter of its original value. In symbols, I ∝ 1/r^2, so I(2r) = I(r)/4. That’s why one quarter is the correct result. The other options don’t fit because they would imply different relationships (half would require a 1/r dependence, unchanged would ignore spreading, and four times greater would mean intensity increases with distance).

The intensity from a point ultraviolet source follows the inverse-square law: it decreases with the square of the distance. When you double the distance, the same power spreads over a surface four times larger, so the energy per unit area drops to one quarter of its original value. In symbols, I ∝ 1/r^2, so I(2r) = I(r)/4. That’s why one quarter is the correct result. The other options don’t fit because they would imply different relationships (half would require a 1/r dependence, unchanged would ignore spreading, and four times greater would mean intensity increases with distance).

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